2004 lines
82 KiB
XML
2004 lines
82 KiB
XML
<title>Image Formats</title>
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<para>The V4L2 API was primarily designed for devices exchanging
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image data with applications. The
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<structname>v4l2_pix_format</structname> and <structname>v4l2_pix_format_mplane
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</structname> structures define the format and layout of an image in memory.
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The former is used with the single-planar API, while the latter is used with the
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multi-planar version (see <xref linkend="planar-apis"/>). Image formats are
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negotiated with the &VIDIOC-S-FMT; ioctl. (The explanations here focus on video
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capturing and output, for overlay frame buffer formats see also
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&VIDIOC-G-FBUF;.)</para>
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<section>
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<title>Single-planar format structure</title>
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<table pgwide="1" frame="none" id="v4l2-pix-format">
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<title>struct <structname>v4l2_pix_format</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>width</structfield></entry>
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<entry>Image width in pixels.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>height</structfield></entry>
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<entry>Image height in pixels. If <structfield>field</structfield> is
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one of <constant>V4L2_FIELD_TOP</constant>, <constant>V4L2_FIELD_BOTTOM</constant>
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or <constant>V4L2_FIELD_ALTERNATE</constant> then height refers to the
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number of lines in the field, otherwise it refers to the number of
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lines in the frame (which is twice the field height for interlaced
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formats).</entry>
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</row>
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<row>
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<entry spanname="hspan">Applications set these fields to
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request an image size, drivers return the closest possible values. In
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case of planar formats the <structfield>width</structfield> and
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<structfield>height</structfield> applies to the largest plane. To
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avoid ambiguities drivers must return values rounded up to a multiple
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of the scale factor of any smaller planes. For example when the image
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format is YUV 4:2:0, <structfield>width</structfield> and
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<structfield>height</structfield> must be multiples of two.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>pixelformat</structfield></entry>
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<entry>The pixel format or type of compression, set by the
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application. This is a little endian <link
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linkend="v4l2-fourcc">four character code</link>. V4L2 defines
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standard RGB formats in <xref linkend="rgb-formats" />, YUV formats in <xref
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linkend="yuv-formats" />, and reserved codes in <xref
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linkend="reserved-formats" /></entry>
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</row>
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<row>
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<entry>&v4l2-field;</entry>
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<entry><structfield>field</structfield></entry>
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<entry>Video images are typically interlaced. Applications
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can request to capture or output only the top or bottom field, or both
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fields interlaced or sequentially stored in one buffer or alternating
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in separate buffers. Drivers return the actual field order selected.
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For more details on fields see <xref linkend="field-order" />.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>bytesperline</structfield></entry>
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<entry>Distance in bytes between the leftmost pixels in two
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adjacent lines.</entry>
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</row>
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<row>
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<entry spanname="hspan"><para>Both applications and drivers
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can set this field to request padding bytes at the end of each line.
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Drivers however may ignore the value requested by the application,
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returning <structfield>width</structfield> times bytes per pixel or a
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larger value required by the hardware. That implies applications can
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just set this field to zero to get a reasonable
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default.</para><para>Video hardware may access padding bytes,
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therefore they must reside in accessible memory. Consider cases where
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padding bytes after the last line of an image cross a system page
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boundary. Input devices may write padding bytes, the value is
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undefined. Output devices ignore the contents of padding
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bytes.</para><para>When the image format is planar the
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<structfield>bytesperline</structfield> value applies to the first
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plane and is divided by the same factor as the
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<structfield>width</structfield> field for the other planes. For
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example the Cb and Cr planes of a YUV 4:2:0 image have half as many
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padding bytes following each line as the Y plane. To avoid ambiguities
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drivers must return a <structfield>bytesperline</structfield> value
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rounded up to a multiple of the scale factor.</para>
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<para>For compressed formats the <structfield>bytesperline</structfield>
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value makes no sense. Applications and drivers must set this to 0 in
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that case.</para></entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>sizeimage</structfield></entry>
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<entry>Size in bytes of the buffer to hold a complete image,
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set by the driver. Usually this is
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<structfield>bytesperline</structfield> times
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<structfield>height</structfield>. When the image consists of variable
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length compressed data this is the maximum number of bytes required to
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hold an image.</entry>
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</row>
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<row>
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<entry>&v4l2-colorspace;</entry>
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<entry><structfield>colorspace</structfield></entry>
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<entry>This information supplements the
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<structfield>pixelformat</structfield> and must be set by the driver for
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capture streams and by the application for output streams,
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see <xref linkend="colorspaces" />.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>priv</structfield></entry>
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<entry><para>This field indicates whether the remaining fields of the
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<structname>v4l2_pix_format</structname> structure, also called the extended
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fields, are valid. When set to <constant>V4L2_PIX_FMT_PRIV_MAGIC</constant>, it
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indicates that the extended fields have been correctly initialized. When set to
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any other value it indicates that the extended fields contain undefined values.
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</para>
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<para>Applications that wish to use the pixel format extended fields must first
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ensure that the feature is supported by querying the device for the
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<link linkend="querycap"><constant>V4L2_CAP_EXT_PIX_FORMAT</constant></link>
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capability. If the capability isn't set the pixel format extended fields are not
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supported and using the extended fields will lead to undefined results.</para>
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<para>To use the extended fields, applications must set the
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<structfield>priv</structfield> field to
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<constant>V4L2_PIX_FMT_PRIV_MAGIC</constant>, initialize all the extended fields
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and zero the unused bytes of the <structname>v4l2_format</structname>
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<structfield>raw_data</structfield> field.</para>
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<para>When the <structfield>priv</structfield> field isn't set to
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<constant>V4L2_PIX_FMT_PRIV_MAGIC</constant> drivers must act as if all the
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extended fields were set to zero. On return drivers must set the
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<structfield>priv</structfield> field to
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<constant>V4L2_PIX_FMT_PRIV_MAGIC</constant> and all the extended fields to
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applicable values.</para></entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry>Flags set by the application or driver, see <xref
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linkend="format-flags" />.</entry>
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</row>
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<row>
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<entry>&v4l2-ycbcr-encoding;</entry>
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<entry><structfield>ycbcr_enc</structfield></entry>
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<entry>This information supplements the
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<structfield>colorspace</structfield> and must be set by the driver for
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capture streams and by the application for output streams,
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see <xref linkend="colorspaces" />.</entry>
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</row>
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<row>
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<entry>&v4l2-quantization;</entry>
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<entry><structfield>quantization</structfield></entry>
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<entry>This information supplements the
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<structfield>colorspace</structfield> and must be set by the driver for
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capture streams and by the application for output streams,
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see <xref linkend="colorspaces" />.</entry>
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</row>
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<row>
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<entry>&v4l2-xfer-func;</entry>
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<entry><structfield>xfer_func</structfield></entry>
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<entry>This information supplements the
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<structfield>colorspace</structfield> and must be set by the driver for
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capture streams and by the application for output streams,
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see <xref linkend="colorspaces" />.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</section>
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<section>
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<title>Multi-planar format structures</title>
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<para>The <structname>v4l2_plane_pix_format</structname> structures define
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size and layout for each of the planes in a multi-planar format.
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The <structname>v4l2_pix_format_mplane</structname> structure contains
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information common to all planes (such as image width and height) and
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an array of <structname>v4l2_plane_pix_format</structname> structures,
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describing all planes of that format.</para>
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<table pgwide="1" frame="none" id="v4l2-plane-pix-format">
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<title>struct <structname>v4l2_plane_pix_format</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>sizeimage</structfield></entry>
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<entry>Maximum size in bytes required for image data in this plane.
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</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>bytesperline</structfield></entry>
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<entry>Distance in bytes between the leftmost pixels in two adjacent
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lines. See &v4l2-pix-format;.</entry>
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</row>
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<row>
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<entry>__u16</entry>
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<entry><structfield>reserved[6]</structfield></entry>
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<entry>Reserved for future extensions. Should be zeroed by drivers and
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applications.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="v4l2-pix-format-mplane">
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<title>struct <structname>v4l2_pix_format_mplane</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>width</structfield></entry>
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<entry>Image width in pixels. See &v4l2-pix-format;.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>height</structfield></entry>
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<entry>Image height in pixels. See &v4l2-pix-format;.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>pixelformat</structfield></entry>
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<entry>The pixel format. Both single- and multi-planar four character
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codes can be used.</entry>
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</row>
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<row>
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<entry>&v4l2-field;</entry>
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<entry><structfield>field</structfield></entry>
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<entry>See &v4l2-pix-format;.</entry>
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</row>
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<row>
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<entry>&v4l2-colorspace;</entry>
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<entry><structfield>colorspace</structfield></entry>
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<entry>See &v4l2-pix-format;.</entry>
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</row>
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<row>
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<entry>&v4l2-plane-pix-format;</entry>
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<entry><structfield>plane_fmt[VIDEO_MAX_PLANES]</structfield></entry>
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<entry>An array of structures describing format of each plane this
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pixel format consists of. The number of valid entries in this array
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has to be put in the <structfield>num_planes</structfield>
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field.</entry>
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</row>
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<row>
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<entry>__u8</entry>
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<entry><structfield>num_planes</structfield></entry>
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<entry>Number of planes (i.e. separate memory buffers) for this format
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and the number of valid entries in the
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<structfield>plane_fmt</structfield> array.</entry>
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</row>
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<row>
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<entry>__u8</entry>
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<entry><structfield>flags</structfield></entry>
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<entry>Flags set by the application or driver, see <xref
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linkend="format-flags" />.</entry>
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</row>
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<row>
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<entry>&v4l2-ycbcr-encoding;</entry>
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<entry><structfield>ycbcr_enc</structfield></entry>
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<entry>This information supplements the
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<structfield>colorspace</structfield> and must be set by the driver for
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capture streams and by the application for output streams,
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see <xref linkend="colorspaces" />.</entry>
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</row>
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<row>
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<entry>&v4l2-quantization;</entry>
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<entry><structfield>quantization</structfield></entry>
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<entry>This information supplements the
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<structfield>colorspace</structfield> and must be set by the driver for
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capture streams and by the application for output streams,
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see <xref linkend="colorspaces" />.</entry>
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</row>
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<row>
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<entry>&v4l2-xfer-func;</entry>
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<entry><structfield>xfer_func</structfield></entry>
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<entry>This information supplements the
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<structfield>colorspace</structfield> and must be set by the driver for
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capture streams and by the application for output streams,
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see <xref linkend="colorspaces" />.</entry>
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</row>
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<row>
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<entry>__u8</entry>
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<entry><structfield>reserved[7]</structfield></entry>
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<entry>Reserved for future extensions. Should be zeroed by drivers
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and applications.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</section>
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<section>
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<title>Standard Image Formats</title>
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<para>In order to exchange images between drivers and
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applications, it is necessary to have standard image data formats
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which both sides will interpret the same way. V4L2 includes several
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such formats, and this section is intended to be an unambiguous
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specification of the standard image data formats in V4L2.</para>
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<para>V4L2 drivers are not limited to these formats, however.
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Driver-specific formats are possible. In that case the application may
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depend on a codec to convert images to one of the standard formats
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when needed. But the data can still be stored and retrieved in the
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proprietary format. For example, a device may support a proprietary
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compressed format. Applications can still capture and save the data in
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the compressed format, saving much disk space, and later use a codec
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to convert the images to the X Windows screen format when the video is
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to be displayed.</para>
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<para>Even so, ultimately, some standard formats are needed, so
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the V4L2 specification would not be complete without well-defined
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standard formats.</para>
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<para>The V4L2 standard formats are mainly uncompressed formats. The
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pixels are always arranged in memory from left to right, and from top
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to bottom. The first byte of data in the image buffer is always for
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the leftmost pixel of the topmost row. Following that is the pixel
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immediately to its right, and so on until the end of the top row of
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pixels. Following the rightmost pixel of the row there may be zero or
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more bytes of padding to guarantee that each row of pixel data has a
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certain alignment. Following the pad bytes, if any, is data for the
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leftmost pixel of the second row from the top, and so on. The last row
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has just as many pad bytes after it as the other rows.</para>
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<para>In V4L2 each format has an identifier which looks like
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<constant>PIX_FMT_XXX</constant>, defined in the <link
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linkend="videodev">videodev2.h</link> header file. These identifiers
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represent <link linkend="v4l2-fourcc">four character (FourCC) codes</link>
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which are also listed below, however they are not the same as those
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used in the Windows world.</para>
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<para>For some formats, data is stored in separate, discontiguous
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memory buffers. Those formats are identified by a separate set of FourCC codes
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and are referred to as "multi-planar formats". For example, a YUV422 frame is
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normally stored in one memory buffer, but it can also be placed in two or three
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separate buffers, with Y component in one buffer and CbCr components in another
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in the 2-planar version or with each component in its own buffer in the
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3-planar case. Those sub-buffers are referred to as "planes".</para>
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</section>
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<section id="colorspaces">
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<title>Colorspaces</title>
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<para>'Color' is a very complex concept and depends on physics, chemistry and
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biology. Just because you have three numbers that describe the 'red', 'green'
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and 'blue' components of the color of a pixel does not mean that you can accurately
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display that color. A colorspace defines what it actually <emphasis>means</emphasis>
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to have an RGB value of e.g. (255, 0, 0). That is, which color should be
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reproduced on the screen in a perfectly calibrated environment.</para>
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<para>In order to do that we first need to have a good definition of
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color, i.e. some way to uniquely and unambiguously define a color so that someone
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else can reproduce it. Human color vision is trichromatic since the human eye has
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color receptors that are sensitive to three different wavelengths of light. Hence
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the need to use three numbers to describe color. Be glad you are not a mantis shrimp
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as those are sensitive to 12 different wavelengths, so instead of RGB we would be
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using the ABCDEFGHIJKL colorspace...</para>
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<para>Color exists only in the eye and brain and is the result of how strongly
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color receptors are stimulated. This is based on the Spectral
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Power Distribution (SPD) which is a graph showing the intensity (radiant power)
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of the light at wavelengths covering the visible spectrum as it enters the eye.
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The science of colorimetry is about the relationship between the SPD and color as
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perceived by the human brain.</para>
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<para>Since the human eye has only three color receptors it is perfectly
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possible that different SPDs will result in the same stimulation of those receptors
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and are perceived as the same color, even though the SPD of the light is
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different.</para>
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<para>In the 1920s experiments were devised to determine the relationship
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between SPDs and the perceived color and that resulted in the CIE 1931 standard
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that defines spectral weighting functions that model the perception of color.
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Specifically that standard defines functions that can take an SPD and calculate
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the stimulus for each color receptor. After some further mathematical transforms
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these stimuli are known as the <emphasis>CIE XYZ tristimulus</emphasis> values
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and these X, Y and Z values describe a color as perceived by a human unambiguously.
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These X, Y and Z values are all in the range [0…1].</para>
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<para>The Y value in the CIE XYZ colorspace corresponds to luminance. Often
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the CIE XYZ colorspace is transformed to the normalized CIE xyY colorspace:</para>
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<para>x = X / (X + Y + Z)</para>
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<para>y = Y / (X + Y + Z)</para>
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<para>The x and y values are the chromaticity coordinates and can be used to
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define a color without the luminance component Y. It is very confusing to
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have such similar names for these colorspaces. Just be aware that if colors
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are specified with lower case 'x' and 'y', then the CIE xyY colorspace is
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used. Upper case 'X' and 'Y' refer to the CIE XYZ colorspace. Also, y has nothing
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to do with luminance. Together x and y specify a color, and Y the luminance.
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That is really all you need to remember from a practical point of view. At
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the end of this section you will find reading resources that go into much more
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detail if you are interested.
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</para>
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<para>A monitor or TV will reproduce colors by emitting light at three
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different wavelengths, the combination of which will stimulate the color receptors
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in the eye and thus cause the perception of color. Historically these wavelengths
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were defined by the red, green and blue phosphors used in the displays. These
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<emphasis>color primaries</emphasis> are part of what defines a colorspace.</para>
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<para>Different display devices will have different primaries and some
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primaries are more suitable for some display technologies than others. This has
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resulted in a variety of colorspaces that are used for different display
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technologies or uses. To define a colorspace you need to define the three
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color primaries (these are typically defined as x, y chromaticity coordinates
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from the CIE xyY colorspace) but also the white reference: that is the color obtained
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when all three primaries are at maximum power. This determines the relative power
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or energy of the primaries. This is usually chosen to be close to daylight which has
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been defined as the CIE D65 Illuminant.</para>
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<para>To recapitulate: the CIE XYZ colorspace uniquely identifies colors.
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Other colorspaces are defined by three chromaticity coordinates defined in the
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CIE xyY colorspace. Based on those a 3x3 matrix can be constructed that
|
|
transforms CIE XYZ colors to colors in the new colorspace.
|
|
</para>
|
|
|
|
<para>Both the CIE XYZ and the RGB colorspace that are derived from the
|
|
specific chromaticity primaries are linear colorspaces. But neither the eye,
|
|
nor display technology is linear. Doubling the values of all components in
|
|
the linear colorspace will not be perceived as twice the intensity of the color.
|
|
So each colorspace also defines a transfer function that takes a linear color
|
|
component value and transforms it to the non-linear component value, which is a
|
|
closer match to the non-linear performance of both the eye and displays. Linear
|
|
component values are denoted RGB, non-linear are denoted as R'G'B'. In general
|
|
colors used in graphics are all R'G'B', except in openGL which uses linear RGB.
|
|
Special care should be taken when dealing with openGL to provide linear RGB colors
|
|
or to use the built-in openGL support to apply the inverse transfer function.</para>
|
|
|
|
<para>The final piece that defines a colorspace is a function that
|
|
transforms non-linear R'G'B' to non-linear Y'CbCr. This function is determined
|
|
by the so-called luma coefficients. There may be multiple possible Y'CbCr
|
|
encodings allowed for the same colorspace. Many encodings of color
|
|
prefer to use luma (Y') and chroma (CbCr) instead of R'G'B'. Since the human
|
|
eye is more sensitive to differences in luminance than in color this encoding
|
|
allows one to reduce the amount of color information compared to the luma
|
|
data. Note that the luma (Y') is unrelated to the Y in the CIE XYZ colorspace.
|
|
Also note that Y'CbCr is often called YCbCr or YUV even though these are
|
|
strictly speaking wrong.</para>
|
|
|
|
<para>Sometimes people confuse Y'CbCr as being a colorspace. This is not
|
|
correct, it is just an encoding of an R'G'B' color into luma and chroma
|
|
values. The underlying colorspace that is associated with the R'G'B' color
|
|
is also associated with the Y'CbCr color.</para>
|
|
|
|
<para>The final step is how the RGB, R'G'B' or Y'CbCr values are
|
|
quantized. The CIE XYZ colorspace where X, Y and Z are in the range
|
|
[0…1] describes all colors that humans can perceive, but the transform to
|
|
another colorspace will produce colors that are outside the [0…1] range.
|
|
Once clamped to the [0…1] range those colors can no longer be reproduced
|
|
in that colorspace. This clamping is what reduces the extent or gamut of the
|
|
colorspace. How the range of [0…1] is translated to integer values in the
|
|
range of [0…255] (or higher, depending on the color depth) is called the
|
|
quantization. This is <emphasis>not</emphasis> part of the colorspace
|
|
definition. In practice RGB or R'G'B' values are full range, i.e. they
|
|
use the full [0…255] range. Y'CbCr values on the other hand are limited
|
|
range with Y' using [16…235] and Cb and Cr using [16…240].</para>
|
|
|
|
<para>Unfortunately, in some cases limited range RGB is also used
|
|
where the components use the range [16…235]. And full range Y'CbCr also exists
|
|
using the [0…255] range.</para>
|
|
|
|
<para>In order to correctly interpret a color you need to know the
|
|
quantization range, whether it is R'G'B' or Y'CbCr, the used Y'CbCr encoding
|
|
and the colorspace.
|
|
From that information you can calculate the corresponding CIE XYZ color
|
|
and map that again to whatever colorspace your display device uses.</para>
|
|
|
|
<para>The colorspace definition itself consists of the three
|
|
chromaticity primaries, the white reference chromaticity, a transfer
|
|
function and the luma coefficients needed to transform R'G'B' to Y'CbCr. While
|
|
some colorspace standards correctly define all four, quite often the colorspace
|
|
standard only defines some, and you have to rely on other standards for
|
|
the missing pieces. The fact that colorspaces are often a mix of different
|
|
standards also led to very confusing naming conventions where the name of
|
|
a standard was used to name a colorspace when in fact that standard was
|
|
part of various other colorspaces as well.</para>
|
|
|
|
<para>If you want to read more about colors and colorspaces, then the
|
|
following resources are useful: <xref linkend="poynton" /> is a good practical
|
|
book for video engineers, <xref linkend="colimg" /> has a much broader scope and
|
|
describes many more aspects of color (physics, chemistry, biology, etc.).
|
|
The <ulink url="http://www.brucelindbloom.com">http://www.brucelindbloom.com</ulink>
|
|
website is an excellent resource, especially with respect to the mathematics behind
|
|
colorspace conversions. The wikipedia <ulink url="http://en.wikipedia.org/wiki/CIE_1931_color_space#CIE_xy_chromaticity_diagram_and_the_CIE_xyY_color_space">CIE 1931 colorspace</ulink> article
|
|
is also very useful.</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Defining Colorspaces in V4L2</title>
|
|
<para>In V4L2 colorspaces are defined by four values. The first is the colorspace
|
|
identifier (&v4l2-colorspace;) which defines the chromaticities, the default transfer
|
|
function, the default Y'CbCr encoding and the default quantization method. The second
|
|
is the transfer function identifier (&v4l2-xfer-func;) to specify non-standard
|
|
transfer functions. The third is the Y'CbCr encoding identifier (&v4l2-ycbcr-encoding;)
|
|
to specify non-standard Y'CbCr encodings and the fourth is the quantization identifier
|
|
(&v4l2-quantization;) to specify non-standard quantization methods. Most of the time
|
|
only the colorspace field of &v4l2-pix-format; or &v4l2-pix-format-mplane; needs to
|
|
be filled in. Note that the default R'G'B' quantization is full range for all
|
|
colorspaces except for BT.2020 which uses limited range R'G'B' quantization.</para>
|
|
|
|
<table pgwide="1" frame="none" id="v4l2-colorspace">
|
|
<title>V4L2 Colorspaces</title>
|
|
<tgroup cols="2" align="left">
|
|
&cs-def;
|
|
<thead>
|
|
<row>
|
|
<entry>Identifier</entry>
|
|
<entry>Details</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_DEFAULT</constant></entry>
|
|
<entry>The default colorspace. This can be used by applications to let the
|
|
driver fill in the colorspace.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_SMPTE170M</constant></entry>
|
|
<entry>See <xref linkend="col-smpte-170m" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_REC709</constant></entry>
|
|
<entry>See <xref linkend="col-rec709" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_SRGB</constant></entry>
|
|
<entry>See <xref linkend="col-srgb" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_ADOBERGB</constant></entry>
|
|
<entry>See <xref linkend="col-adobergb" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_BT2020</constant></entry>
|
|
<entry>See <xref linkend="col-bt2020" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_DCI_P3</constant></entry>
|
|
<entry>See <xref linkend="col-dcip3" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_SMPTE240M</constant></entry>
|
|
<entry>See <xref linkend="col-smpte-240m" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_470_SYSTEM_M</constant></entry>
|
|
<entry>See <xref linkend="col-sysm" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_470_SYSTEM_BG</constant></entry>
|
|
<entry>See <xref linkend="col-sysbg" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_JPEG</constant></entry>
|
|
<entry>See <xref linkend="col-jpeg" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_COLORSPACE_RAW</constant></entry>
|
|
<entry>The raw colorspace. This is used for raw image capture where
|
|
the image is minimally processed and is using the internal colorspace
|
|
of the device. The software that processes an image using this
|
|
'colorspace' will have to know the internals of the capture device.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<table pgwide="1" frame="none" id="v4l2-xfer-func">
|
|
<title>V4L2 Transfer Function</title>
|
|
<tgroup cols="2" align="left">
|
|
&cs-def;
|
|
<thead>
|
|
<row>
|
|
<entry>Identifier</entry>
|
|
<entry>Details</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry><constant>V4L2_XFER_FUNC_DEFAULT</constant></entry>
|
|
<entry>Use the default transfer function as defined by the colorspace.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_XFER_FUNC_709</constant></entry>
|
|
<entry>Use the Rec. 709 transfer function.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_XFER_FUNC_SRGB</constant></entry>
|
|
<entry>Use the sRGB transfer function.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_XFER_FUNC_ADOBERGB</constant></entry>
|
|
<entry>Use the AdobeRGB transfer function.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_XFER_FUNC_SMPTE240M</constant></entry>
|
|
<entry>Use the SMPTE 240M transfer function.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_XFER_FUNC_NONE</constant></entry>
|
|
<entry>Do not use a transfer function (i.e. use linear RGB values).</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_XFER_FUNC_DCI_P3</constant></entry>
|
|
<entry>Use the DCI-P3 transfer function.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_XFER_FUNC_SMPTE2084</constant></entry>
|
|
<entry>Use the SMPTE 2084 transfer function.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<table pgwide="1" frame="none" id="v4l2-ycbcr-encoding">
|
|
<title>V4L2 Y'CbCr Encodings</title>
|
|
<tgroup cols="2" align="left">
|
|
&cs-def;
|
|
<thead>
|
|
<row>
|
|
<entry>Identifier</entry>
|
|
<entry>Details</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry><constant>V4L2_YCBCR_ENC_DEFAULT</constant></entry>
|
|
<entry>Use the default Y'CbCr encoding as defined by the colorspace.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_YCBCR_ENC_601</constant></entry>
|
|
<entry>Use the BT.601 Y'CbCr encoding.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_YCBCR_ENC_709</constant></entry>
|
|
<entry>Use the Rec. 709 Y'CbCr encoding.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_YCBCR_ENC_XV601</constant></entry>
|
|
<entry>Use the extended gamut xvYCC BT.601 encoding.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_YCBCR_ENC_XV709</constant></entry>
|
|
<entry>Use the extended gamut xvYCC Rec. 709 encoding.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_YCBCR_ENC_SYCC</constant></entry>
|
|
<entry>Use the extended gamut sYCC encoding.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_YCBCR_ENC_BT2020</constant></entry>
|
|
<entry>Use the default non-constant luminance BT.2020 Y'CbCr encoding.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_YCBCR_ENC_BT2020_CONST_LUM</constant></entry>
|
|
<entry>Use the constant luminance BT.2020 Yc'CbcCrc encoding.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<table pgwide="1" frame="none" id="v4l2-quantization">
|
|
<title>V4L2 Quantization Methods</title>
|
|
<tgroup cols="2" align="left">
|
|
&cs-def;
|
|
<thead>
|
|
<row>
|
|
<entry>Identifier</entry>
|
|
<entry>Details</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry><constant>V4L2_QUANTIZATION_DEFAULT</constant></entry>
|
|
<entry>Use the default quantization encoding as defined by the colorspace.
|
|
This is always full range for R'G'B' (except for the BT.2020 colorspace) and usually
|
|
limited range for Y'CbCr.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_QUANTIZATION_FULL_RANGE</constant></entry>
|
|
<entry>Use the full range quantization encoding. I.e. the range [0…1]
|
|
is mapped to [0…255] (with possible clipping to [1…254] to avoid the
|
|
0x00 and 0xff values). Cb and Cr are mapped from [-0.5…0.5] to [0…255]
|
|
(with possible clipping to [1…254] to avoid the 0x00 and 0xff values).</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_QUANTIZATION_LIM_RANGE</constant></entry>
|
|
<entry>Use the limited range quantization encoding. I.e. the range [0…1]
|
|
is mapped to [16…235]. Cb and Cr are mapped from [-0.5…0.5] to [16…240].
|
|
</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Detailed Colorspace Descriptions</title>
|
|
<section id="col-smpte-170m">
|
|
<title>Colorspace SMPTE 170M (<constant>V4L2_COLORSPACE_SMPTE170M</constant>)</title>
|
|
<para>The <xref linkend="smpte170m" /> standard defines the colorspace used by NTSC and PAL and by SDTV
|
|
in general. The default transfer function is <constant>V4L2_XFER_FUNC_709</constant>.
|
|
The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_601</constant>.
|
|
The default Y'CbCr quantization is limited range. The chromaticities of the primary colors and
|
|
the white reference are:</para>
|
|
<table frame="none">
|
|
<title>SMPTE 170M Chromaticities</title>
|
|
<tgroup cols="3" align="left">
|
|
&cs-str;
|
|
<thead>
|
|
<row>
|
|
<entry>Color</entry>
|
|
<entry>x</entry>
|
|
<entry>y</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>Red</entry>
|
|
<entry>0.630</entry>
|
|
<entry>0.340</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Green</entry>
|
|
<entry>0.310</entry>
|
|
<entry>0.595</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Blue</entry>
|
|
<entry>0.155</entry>
|
|
<entry>0.070</entry>
|
|
</row>
|
|
<row>
|
|
<entry>White Reference (D65)</entry>
|
|
<entry>0.3127</entry>
|
|
<entry>0.3290</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
<para>The red, green and blue chromaticities are also often referred to
|
|
as the SMPTE C set, so this colorspace is sometimes called SMPTE C as well.</para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The transfer function defined for SMPTE 170M is the same as the
|
|
one defined in Rec. 709.</term>
|
|
<listitem>
|
|
<para>L' = -1.099(-L)<superscript>0.45</superscript> + 0.099 for L ≤ -0.018</para>
|
|
<para>L' = 4.5L for -0.018 < L < 0.018</para>
|
|
<para>L' = 1.099L<superscript>0.45</superscript> - 0.099 for L ≥ 0.018</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Inverse Transfer function:</term>
|
|
<listitem>
|
|
<para>L = -((L' - 0.099) / -1.099)<superscript>1/0.45</superscript> for L' ≤ -0.081</para>
|
|
<para>L = L' / 4.5 for -0.081 < L' < 0.081</para>
|
|
<para>L = ((L' + 0.099) / 1.099)<superscript>1/0.45</superscript> for L' ≥ 0.081</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The luminance (Y') and color difference (Cb and Cr) are obtained with
|
|
the following <constant>V4L2_YCBCR_ENC_601</constant> encoding:</term>
|
|
<listitem>
|
|
<para>Y' = 0.299R' + 0.587G' + 0.114B'</para>
|
|
<para>Cb = -0.169R' - 0.331G' + 0.5B'</para>
|
|
<para>Cr = 0.5R' - 0.419G' - 0.081B'</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>Y' is clamped to the range [0…1] and Cb and Cr are
|
|
clamped to the range [-0.5…0.5]. This conversion to Y'CbCr is identical to the one
|
|
defined in the <xref linkend="itu601" /> standard and this colorspace is sometimes called BT.601 as well, even
|
|
though BT.601 does not mention any color primaries.</para>
|
|
<para>The default quantization is limited range, but full range is possible although
|
|
rarely seen.</para>
|
|
</section>
|
|
|
|
<section id="col-rec709">
|
|
<title>Colorspace Rec. 709 (<constant>V4L2_COLORSPACE_REC709</constant>)</title>
|
|
<para>The <xref linkend="itu709" /> standard defines the colorspace used by HDTV in general.
|
|
The default transfer function is <constant>V4L2_XFER_FUNC_709</constant>. The default
|
|
Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_709</constant>. The default Y'CbCr quantization is
|
|
limited range. The chromaticities of the primary colors and the white reference are:</para>
|
|
<table frame="none">
|
|
<title>Rec. 709 Chromaticities</title>
|
|
<tgroup cols="3" align="left">
|
|
&cs-str;
|
|
<thead>
|
|
<row>
|
|
<entry>Color</entry>
|
|
<entry>x</entry>
|
|
<entry>y</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>Red</entry>
|
|
<entry>0.640</entry>
|
|
<entry>0.330</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Green</entry>
|
|
<entry>0.300</entry>
|
|
<entry>0.600</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Blue</entry>
|
|
<entry>0.150</entry>
|
|
<entry>0.060</entry>
|
|
</row>
|
|
<row>
|
|
<entry>White Reference (D65)</entry>
|
|
<entry>0.3127</entry>
|
|
<entry>0.3290</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
<para>The full name of this standard is Rec. ITU-R BT.709-5.</para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Transfer function. Normally L is in the range [0…1], but for the extended
|
|
gamut xvYCC encoding values outside that range are allowed.</term>
|
|
<listitem>
|
|
<para>L' = -1.099(-L)<superscript>0.45</superscript> + 0.099 for L ≤ -0.018</para>
|
|
<para>L' = 4.5L for -0.018 < L < 0.018</para>
|
|
<para>L' = 1.099L<superscript>0.45</superscript> - 0.099 for L ≥ 0.018</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Inverse Transfer function:</term>
|
|
<listitem>
|
|
<para>L = -((L' - 0.099) / -1.099)<superscript>1/0.45</superscript> for L' ≤ -0.081</para>
|
|
<para>L = L' / 4.5 for -0.081 < L' < 0.081</para>
|
|
<para>L = ((L' + 0.099) / 1.099)<superscript>1/0.45</superscript> for L' ≥ 0.081</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The luminance (Y') and color difference (Cb and Cr) are obtained with the following
|
|
<constant>V4L2_YCBCR_ENC_709</constant> encoding:</term>
|
|
<listitem>
|
|
<para>Y' = 0.2126R' + 0.7152G' + 0.0722B'</para>
|
|
<para>Cb = -0.1146R' - 0.3854G' + 0.5B'</para>
|
|
<para>Cr = 0.5R' - 0.4542G' - 0.0458B'</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>Y' is clamped to the range [0…1] and Cb and Cr are
|
|
clamped to the range [-0.5…0.5].</para>
|
|
<para>The default quantization is limited range, but full range is possible although
|
|
rarely seen.</para>
|
|
<para>The <constant>V4L2_YCBCR_ENC_709</constant> encoding described above is the default
|
|
for this colorspace, but it can be overridden with <constant>V4L2_YCBCR_ENC_601</constant>, in which
|
|
case the BT.601 Y'CbCr encoding is used.</para>
|
|
<para>Two additional extended gamut Y'CbCr encodings are also possible with this colorspace:</para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The xvYCC 709 encoding (<constant>V4L2_YCBCR_ENC_XV709</constant>, <xref linkend="xvycc" />)
|
|
is similar to the Rec. 709 encoding, but it allows for R', G' and B' values that are outside the range
|
|
[0…1]. The resulting Y', Cb and Cr values are scaled and offset:</term>
|
|
<listitem>
|
|
<para>Y' = (219 / 256) * (0.2126R' + 0.7152G' + 0.0722B') + (16 / 256)</para>
|
|
<para>Cb = (224 / 256) * (-0.1146R' - 0.3854G' + 0.5B')</para>
|
|
<para>Cr = (224 / 256) * (0.5R' - 0.4542G' - 0.0458B')</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The xvYCC 601 encoding (<constant>V4L2_YCBCR_ENC_XV601</constant>, <xref linkend="xvycc" />) is similar
|
|
to the BT.601 encoding, but it allows for R', G' and B' values that are outside the range
|
|
[0…1]. The resulting Y', Cb and Cr values are scaled and offset:</term>
|
|
<listitem>
|
|
<para>Y' = (219 / 256) * (0.299R' + 0.587G' + 0.114B') + (16 / 256)</para>
|
|
<para>Cb = (224 / 256) * (-0.169R' - 0.331G' + 0.5B')</para>
|
|
<para>Cr = (224 / 256) * (0.5R' - 0.419G' - 0.081B')</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>Y' is clamped to the range [0…1] and Cb and Cr are clamped
|
|
to the range [-0.5…0.5]. The non-standard xvYCC 709 or xvYCC 601 encodings can be used by
|
|
selecting <constant>V4L2_YCBCR_ENC_XV709</constant> or <constant>V4L2_YCBCR_ENC_XV601</constant>.
|
|
The xvYCC encodings always use full range quantization.</para>
|
|
</section>
|
|
|
|
<section id="col-srgb">
|
|
<title>Colorspace sRGB (<constant>V4L2_COLORSPACE_SRGB</constant>)</title>
|
|
<para>The <xref linkend="srgb" /> standard defines the colorspace used by most webcams
|
|
and computer graphics. The default transfer function is <constant>V4L2_XFER_FUNC_SRGB</constant>.
|
|
The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_SYCC</constant>. The default Y'CbCr
|
|
quantization is full range. The chromaticities of the primary colors and the white
|
|
reference are:</para>
|
|
<table frame="none">
|
|
<title>sRGB Chromaticities</title>
|
|
<tgroup cols="3" align="left">
|
|
&cs-str;
|
|
<thead>
|
|
<row>
|
|
<entry>Color</entry>
|
|
<entry>x</entry>
|
|
<entry>y</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>Red</entry>
|
|
<entry>0.640</entry>
|
|
<entry>0.330</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Green</entry>
|
|
<entry>0.300</entry>
|
|
<entry>0.600</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Blue</entry>
|
|
<entry>0.150</entry>
|
|
<entry>0.060</entry>
|
|
</row>
|
|
<row>
|
|
<entry>White Reference (D65)</entry>
|
|
<entry>0.3127</entry>
|
|
<entry>0.3290</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
<para>These chromaticities are identical to the Rec. 709 colorspace.</para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Transfer function. Note that negative values for L are only used by the Y'CbCr conversion.</term>
|
|
<listitem>
|
|
<para>L' = -1.055(-L)<superscript>1/2.4</superscript> + 0.055 for L < -0.0031308</para>
|
|
<para>L' = 12.92L for -0.0031308 ≤ L ≤ 0.0031308</para>
|
|
<para>L' = 1.055L<superscript>1/2.4</superscript> - 0.055 for 0.0031308 < L ≤ 1</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Inverse Transfer function:</term>
|
|
<listitem>
|
|
<para>L = -((-L' + 0.055) / 1.055)<superscript>2.4</superscript> for L' < -0.04045</para>
|
|
<para>L = L' / 12.92 for -0.04045 ≤ L' ≤ 0.04045</para>
|
|
<para>L = ((L' + 0.055) / 1.055)<superscript>2.4</superscript> for L' > 0.04045</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The luminance (Y') and color difference (Cb and Cr) are obtained with the following
|
|
<constant>V4L2_YCBCR_ENC_SYCC</constant> encoding as defined by <xref linkend="sycc" />:</term>
|
|
<listitem>
|
|
<para>Y' = 0.2990R' + 0.5870G' + 0.1140B'</para>
|
|
<para>Cb = -0.1687R' - 0.3313G' + 0.5B'</para>
|
|
<para>Cr = 0.5R' - 0.4187G' - 0.0813B'</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>Y' is clamped to the range [0…1] and Cb and Cr are clamped
|
|
to the range [-0.5…0.5]. The <constant>V4L2_YCBCR_ENC_SYCC</constant> quantization is always
|
|
full range. Although this Y'CbCr encoding looks very similar to the <constant>V4L2_YCBCR_ENC_XV601</constant>
|
|
encoding, it is not. The <constant>V4L2_YCBCR_ENC_XV601</constant> scales and offsets the Y'CbCr
|
|
values before quantization, but this encoding does not do that.</para>
|
|
</section>
|
|
|
|
<section id="col-adobergb">
|
|
<title>Colorspace Adobe RGB (<constant>V4L2_COLORSPACE_ADOBERGB</constant>)</title>
|
|
<para>The <xref linkend="adobergb" /> standard defines the colorspace used by computer graphics
|
|
that use the AdobeRGB colorspace. This is also known as the <xref linkend="oprgb" /> standard.
|
|
The default transfer function is <constant>V4L2_XFER_FUNC_ADOBERGB</constant>.
|
|
The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_601</constant>. The default Y'CbCr
|
|
quantization is limited range. The chromaticities of the primary colors and the white reference
|
|
are:</para>
|
|
<table frame="none">
|
|
<title>Adobe RGB Chromaticities</title>
|
|
<tgroup cols="3" align="left">
|
|
&cs-str;
|
|
<thead>
|
|
<row>
|
|
<entry>Color</entry>
|
|
<entry>x</entry>
|
|
<entry>y</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>Red</entry>
|
|
<entry>0.6400</entry>
|
|
<entry>0.3300</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Green</entry>
|
|
<entry>0.2100</entry>
|
|
<entry>0.7100</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Blue</entry>
|
|
<entry>0.1500</entry>
|
|
<entry>0.0600</entry>
|
|
</row>
|
|
<row>
|
|
<entry>White Reference (D65)</entry>
|
|
<entry>0.3127</entry>
|
|
<entry>0.3290</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Transfer function:</term>
|
|
<listitem>
|
|
<para>L' = L<superscript>1/2.19921875</superscript></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Inverse Transfer function:</term>
|
|
<listitem>
|
|
<para>L = L'<superscript>2.19921875</superscript></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The luminance (Y') and color difference (Cb and Cr) are obtained with the
|
|
following <constant>V4L2_YCBCR_ENC_601</constant> encoding:</term>
|
|
<listitem>
|
|
<para>Y' = 0.299R' + 0.587G' + 0.114B'</para>
|
|
<para>Cb = -0.169R' - 0.331G' + 0.5B'</para>
|
|
<para>Cr = 0.5R' - 0.419G' - 0.081B'</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>Y' is clamped to the range [0…1] and Cb and Cr are
|
|
clamped to the range [-0.5…0.5]. This transform is identical to one defined in
|
|
SMPTE 170M/BT.601. The Y'CbCr quantization is limited range.</para>
|
|
</section>
|
|
|
|
<section id="col-bt2020">
|
|
<title>Colorspace BT.2020 (<constant>V4L2_COLORSPACE_BT2020</constant>)</title>
|
|
<para>The <xref linkend="itu2020" /> standard defines the colorspace used by Ultra-high definition
|
|
television (UHDTV). The default transfer function is <constant>V4L2_XFER_FUNC_709</constant>.
|
|
The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_BT2020</constant>.
|
|
The default R'G'B' quantization is limited range (!), and so is the default Y'CbCr quantization.
|
|
The chromaticities of the primary colors and the white reference are:</para>
|
|
<table frame="none">
|
|
<title>BT.2020 Chromaticities</title>
|
|
<tgroup cols="3" align="left">
|
|
&cs-str;
|
|
<thead>
|
|
<row>
|
|
<entry>Color</entry>
|
|
<entry>x</entry>
|
|
<entry>y</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>Red</entry>
|
|
<entry>0.708</entry>
|
|
<entry>0.292</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Green</entry>
|
|
<entry>0.170</entry>
|
|
<entry>0.797</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Blue</entry>
|
|
<entry>0.131</entry>
|
|
<entry>0.046</entry>
|
|
</row>
|
|
<row>
|
|
<entry>White Reference (D65)</entry>
|
|
<entry>0.3127</entry>
|
|
<entry>0.3290</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Transfer function (same as Rec. 709):</term>
|
|
<listitem>
|
|
<para>L' = 4.5L for 0 ≤ L < 0.018</para>
|
|
<para>L' = 1.099L<superscript>0.45</superscript> - 0.099 for 0.018 ≤ L ≤ 1</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Inverse Transfer function:</term>
|
|
<listitem>
|
|
<para>L = L' / 4.5 for L' < 0.081</para>
|
|
<para>L = ((L' + 0.099) / 1.099)<superscript>1/0.45</superscript> for L' ≥ 0.081</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The luminance (Y') and color difference (Cb and Cr) are obtained with the
|
|
following <constant>V4L2_YCBCR_ENC_BT2020</constant> encoding:</term>
|
|
<listitem>
|
|
<para>Y' = 0.2627R' + 0.6780G' + 0.0593B'</para>
|
|
<para>Cb = -0.1396R' - 0.3604G' + 0.5B'</para>
|
|
<para>Cr = 0.5R' - 0.4598G' - 0.0402B'</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>Y' is clamped to the range [0…1] and Cb and Cr are
|
|
clamped to the range [-0.5…0.5]. The Y'CbCr quantization is limited range.</para>
|
|
<para>There is also an alternate constant luminance R'G'B' to Yc'CbcCrc
|
|
(<constant>V4L2_YCBCR_ENC_BT2020_CONST_LUM</constant>) encoding:</para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Luma:</term>
|
|
<listitem>
|
|
<para>Yc' = (0.2627R + 0.6780G + 0.0593B)'</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>B' - Yc' ≤ 0:</term>
|
|
<listitem>
|
|
<para>Cbc = (B' - Yc') / 1.9404</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>B' - Yc' > 0:</term>
|
|
<listitem>
|
|
<para>Cbc = (B' - Yc') / 1.5816</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>R' - Yc' ≤ 0:</term>
|
|
<listitem>
|
|
<para>Crc = (R' - Y') / 1.7184</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>R' - Yc' > 0:</term>
|
|
<listitem>
|
|
<para>Crc = (R' - Y') / 0.9936</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>Yc' is clamped to the range [0…1] and Cbc and Crc are
|
|
clamped to the range [-0.5…0.5]. The Yc'CbcCrc quantization is limited range.</para>
|
|
</section>
|
|
|
|
<section id="col-dcip3">
|
|
<title>Colorspace DCI-P3 (<constant>V4L2_COLORSPACE_DCI_P3</constant>)</title>
|
|
<para>The <xref linkend="smpte431" /> standard defines the colorspace used by cinema
|
|
projectors that use the DCI-P3 colorspace.
|
|
The default transfer function is <constant>V4L2_XFER_FUNC_DCI_P3</constant>.
|
|
The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_709</constant>. Note that this
|
|
colorspace does not specify a Y'CbCr encoding since it is not meant to be encoded
|
|
to Y'CbCr. So this default Y'CbCr encoding was picked because it is the HDTV
|
|
encoding. The default Y'CbCr quantization is limited range. The chromaticities of
|
|
the primary colors and the white reference are:</para>
|
|
<table frame="none">
|
|
<title>DCI-P3 Chromaticities</title>
|
|
<tgroup cols="3" align="left">
|
|
&cs-str;
|
|
<thead>
|
|
<row>
|
|
<entry>Color</entry>
|
|
<entry>x</entry>
|
|
<entry>y</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>Red</entry>
|
|
<entry>0.6800</entry>
|
|
<entry>0.3200</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Green</entry>
|
|
<entry>0.2650</entry>
|
|
<entry>0.6900</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Blue</entry>
|
|
<entry>0.1500</entry>
|
|
<entry>0.0600</entry>
|
|
</row>
|
|
<row>
|
|
<entry>White Reference</entry>
|
|
<entry>0.3140</entry>
|
|
<entry>0.3510</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Transfer function:</term>
|
|
<listitem>
|
|
<para>L' = L<superscript>1/2.6</superscript></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Inverse Transfer function:</term>
|
|
<listitem>
|
|
<para>L = L'<superscript>2.6</superscript></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>Y'CbCr encoding is not specified. V4L2 defaults to Rec. 709.</para>
|
|
</section>
|
|
|
|
<section id="col-smpte-240m">
|
|
<title>Colorspace SMPTE 240M (<constant>V4L2_COLORSPACE_SMPTE240M</constant>)</title>
|
|
<para>The <xref linkend="smpte240m" /> standard was an interim standard used during
|
|
the early days of HDTV (1988-1998). It has been superseded by Rec. 709.
|
|
The default transfer function is <constant>V4L2_XFER_FUNC_SMPTE240M</constant>.
|
|
The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_SMPTE240M</constant>.
|
|
The default Y'CbCr quantization is limited range. The chromaticities of the primary colors and the
|
|
white reference are:</para>
|
|
<table frame="none">
|
|
<title>SMPTE 240M Chromaticities</title>
|
|
<tgroup cols="3" align="left">
|
|
&cs-str;
|
|
<thead>
|
|
<row>
|
|
<entry>Color</entry>
|
|
<entry>x</entry>
|
|
<entry>y</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>Red</entry>
|
|
<entry>0.630</entry>
|
|
<entry>0.340</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Green</entry>
|
|
<entry>0.310</entry>
|
|
<entry>0.595</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Blue</entry>
|
|
<entry>0.155</entry>
|
|
<entry>0.070</entry>
|
|
</row>
|
|
<row>
|
|
<entry>White Reference (D65)</entry>
|
|
<entry>0.3127</entry>
|
|
<entry>0.3290</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
<para>These chromaticities are identical to the SMPTE 170M colorspace.</para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Transfer function:</term>
|
|
<listitem>
|
|
<para>L' = 4L for 0 ≤ L < 0.0228</para>
|
|
<para>L' = 1.1115L<superscript>0.45</superscript> - 0.1115 for 0.0228 ≤ L ≤ 1</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Inverse Transfer function:</term>
|
|
<listitem>
|
|
<para>L = L' / 4 for 0 ≤ L' < 0.0913</para>
|
|
<para>L = ((L' + 0.1115) / 1.1115)<superscript>1/0.45</superscript> for L' ≥ 0.0913</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The luminance (Y') and color difference (Cb and Cr) are obtained with the
|
|
following <constant>V4L2_YCBCR_ENC_SMPTE240M</constant> encoding:</term>
|
|
<listitem>
|
|
<para>Y' = 0.2122R' + 0.7013G' + 0.0865B'</para>
|
|
<para>Cb = -0.1161R' - 0.3839G' + 0.5B'</para>
|
|
<para>Cr = 0.5R' - 0.4451G' - 0.0549B'</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>Yc' is clamped to the range [0…1] and Cbc and Crc are
|
|
clamped to the range [-0.5…0.5]. The Y'CbCr quantization is limited range.</para>
|
|
</section>
|
|
|
|
<section id="col-sysm">
|
|
<title>Colorspace NTSC 1953 (<constant>V4L2_COLORSPACE_470_SYSTEM_M</constant>)</title>
|
|
<para>This standard defines the colorspace used by NTSC in 1953. In practice this
|
|
colorspace is obsolete and SMPTE 170M should be used instead.
|
|
The default transfer function is <constant>V4L2_XFER_FUNC_709</constant>.
|
|
The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_601</constant>.
|
|
The default Y'CbCr quantization is limited range.
|
|
The chromaticities of the primary colors and the white reference are:</para>
|
|
<table frame="none">
|
|
<title>NTSC 1953 Chromaticities</title>
|
|
<tgroup cols="3" align="left">
|
|
&cs-str;
|
|
<thead>
|
|
<row>
|
|
<entry>Color</entry>
|
|
<entry>x</entry>
|
|
<entry>y</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>Red</entry>
|
|
<entry>0.67</entry>
|
|
<entry>0.33</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Green</entry>
|
|
<entry>0.21</entry>
|
|
<entry>0.71</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Blue</entry>
|
|
<entry>0.14</entry>
|
|
<entry>0.08</entry>
|
|
</row>
|
|
<row>
|
|
<entry>White Reference (C)</entry>
|
|
<entry>0.310</entry>
|
|
<entry>0.316</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
<para>Note that this colorspace uses Illuminant C instead of D65 as the
|
|
white reference. To correctly convert an image in this colorspace to another
|
|
that uses D65 you need to apply a chromatic adaptation algorithm such as the
|
|
Bradford method.</para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The transfer function was never properly defined for NTSC 1953. The
|
|
Rec. 709 transfer function is recommended in the literature:</term>
|
|
<listitem>
|
|
<para>L' = 4.5L for 0 ≤ L < 0.018</para>
|
|
<para>L' = 1.099L<superscript>0.45</superscript> - 0.099 for 0.018 ≤ L ≤ 1</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Inverse Transfer function:</term>
|
|
<listitem>
|
|
<para>L = L' / 4.5 for L' < 0.081</para>
|
|
<para>L = ((L' + 0.099) / 1.099)<superscript>1/0.45</superscript> for L' ≥ 0.081</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The luminance (Y') and color difference (Cb and Cr) are obtained with the
|
|
following <constant>V4L2_YCBCR_ENC_601</constant> encoding:</term>
|
|
<listitem>
|
|
<para>Y' = 0.299R' + 0.587G' + 0.114B'</para>
|
|
<para>Cb = -0.169R' - 0.331G' + 0.5B'</para>
|
|
<para>Cr = 0.5R' - 0.419G' - 0.081B'</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>Y' is clamped to the range [0…1] and Cb and Cr are
|
|
clamped to the range [-0.5…0.5]. The Y'CbCr quantization is limited range.
|
|
This transform is identical to one defined in SMPTE 170M/BT.601.</para>
|
|
</section>
|
|
|
|
<section id="col-sysbg">
|
|
<title>Colorspace EBU Tech. 3213 (<constant>V4L2_COLORSPACE_470_SYSTEM_BG</constant>)</title>
|
|
<para>The <xref linkend="tech3213" /> standard defines the colorspace used by PAL/SECAM in 1975. In practice this
|
|
colorspace is obsolete and SMPTE 170M should be used instead.
|
|
The default transfer function is <constant>V4L2_XFER_FUNC_709</constant>.
|
|
The default Y'CbCr encoding is <constant>V4L2_YCBCR_ENC_601</constant>.
|
|
The default Y'CbCr quantization is limited range.
|
|
The chromaticities of the primary colors and the white reference are:</para>
|
|
<table frame="none">
|
|
<title>EBU Tech. 3213 Chromaticities</title>
|
|
<tgroup cols="3" align="left">
|
|
&cs-str;
|
|
<thead>
|
|
<row>
|
|
<entry>Color</entry>
|
|
<entry>x</entry>
|
|
<entry>y</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>Red</entry>
|
|
<entry>0.64</entry>
|
|
<entry>0.33</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Green</entry>
|
|
<entry>0.29</entry>
|
|
<entry>0.60</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Blue</entry>
|
|
<entry>0.15</entry>
|
|
<entry>0.06</entry>
|
|
</row>
|
|
<row>
|
|
<entry>White Reference (D65)</entry>
|
|
<entry>0.3127</entry>
|
|
<entry>0.3290</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The transfer function was never properly defined for this colorspace.
|
|
The Rec. 709 transfer function is recommended in the literature:</term>
|
|
<listitem>
|
|
<para>L' = 4.5L for 0 ≤ L < 0.018</para>
|
|
<para>L' = 1.099L<superscript>0.45</superscript> - 0.099 for 0.018 ≤ L ≤ 1</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Inverse Transfer function:</term>
|
|
<listitem>
|
|
<para>L = L' / 4.5 for L' < 0.081</para>
|
|
<para>L = ((L' + 0.099) / 1.099)<superscript>1/0.45</superscript> for L' ≥ 0.081</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>The luminance (Y') and color difference (Cb and Cr) are obtained with the
|
|
following <constant>V4L2_YCBCR_ENC_601</constant> encoding:</term>
|
|
<listitem>
|
|
<para>Y' = 0.299R' + 0.587G' + 0.114B'</para>
|
|
<para>Cb = -0.169R' - 0.331G' + 0.5B'</para>
|
|
<para>Cr = 0.5R' - 0.419G' - 0.081B'</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>Y' is clamped to the range [0…1] and Cb and Cr are
|
|
clamped to the range [-0.5…0.5]. The Y'CbCr quantization is limited range.
|
|
This transform is identical to one defined in SMPTE 170M/BT.601.</para>
|
|
</section>
|
|
|
|
<section id="col-jpeg">
|
|
<title>Colorspace JPEG (<constant>V4L2_COLORSPACE_JPEG</constant>)</title>
|
|
<para>This colorspace defines the colorspace used by most (Motion-)JPEG formats. The chromaticities
|
|
of the primary colors and the white reference are identical to sRGB. The transfer
|
|
function use is <constant>V4L2_XFER_FUNC_SRGB</constant>. The Y'CbCr encoding is
|
|
<constant>V4L2_YCBCR_ENC_601</constant> with full range quantization where
|
|
Y' is scaled to [0…255] and Cb/Cr are scaled to [-128…128] and
|
|
then clipped to [-128…127].</para>
|
|
<para>Note that the JPEG standard does not actually store colorspace information.
|
|
So if something other than sRGB is used, then the driver will have to set that information
|
|
explicitly. Effectively <constant>V4L2_COLORSPACE_JPEG</constant> can be considered to be
|
|
an abbreviation for <constant>V4L2_COLORSPACE_SRGB</constant>, <constant>V4L2_YCBCR_ENC_601</constant>
|
|
and <constant>V4L2_QUANTIZATION_FULL_RANGE</constant>.</para>
|
|
</section>
|
|
|
|
</section>
|
|
|
|
<section>
|
|
<title>Detailed Transfer Function Descriptions</title>
|
|
<section id="xf-smpte-2084">
|
|
<title>Transfer Function SMPTE 2084 (<constant>V4L2_XFER_FUNC_SMPTE2084</constant>)</title>
|
|
<para>The <xref linkend="smpte2084" /> standard defines the transfer function used by
|
|
High Dynamic Range content.</para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Constants:</term>
|
|
<listitem>
|
|
<para>m1 = (2610 / 4096) / 4</para>
|
|
<para>m2 = (2523 / 4096) * 128</para>
|
|
<para>c1 = 3424 / 4096</para>
|
|
<para>c2 = (2413 / 4096) * 32</para>
|
|
<para>c3 = (2392 / 4096) * 32</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>Transfer function:</term>
|
|
<listitem>
|
|
<para>L' = ((c1 + c2 * L<superscript>m1</superscript>) / (1 + c3 * L<superscript>m1</superscript>))<superscript>m2</superscript></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>Inverse Transfer function:</term>
|
|
<listitem>
|
|
<para>L = (max(L'<superscript>1/m2</superscript> - c1, 0) / (c2 - c3 * L'<superscript>1/m2</superscript>))<superscript>1/m1</superscript></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="pixfmt-indexed">
|
|
<title>Indexed Format</title>
|
|
|
|
<para>In this format each pixel is represented by an 8 bit index
|
|
into a 256 entry ARGB palette. It is intended for <link
|
|
linkend="osd">Video Output Overlays</link> only. There are no ioctls to
|
|
access the palette, this must be done with ioctls of the Linux framebuffer API.</para>
|
|
|
|
<table pgwide="0" frame="none">
|
|
<title>Indexed Image Format</title>
|
|
<tgroup cols="37" align="center">
|
|
<colspec colname="id" align="left" />
|
|
<colspec colname="fourcc" />
|
|
<colspec colname="bit" />
|
|
|
|
<colspec colnum="4" colname="b07" align="center" />
|
|
<colspec colnum="5" colname="b06" align="center" />
|
|
<colspec colnum="6" colname="b05" align="center" />
|
|
<colspec colnum="7" colname="b04" align="center" />
|
|
<colspec colnum="8" colname="b03" align="center" />
|
|
<colspec colnum="9" colname="b02" align="center" />
|
|
<colspec colnum="10" colname="b01" align="center" />
|
|
<colspec colnum="11" colname="b00" align="center" />
|
|
|
|
<spanspec namest="b07" nameend="b00" spanname="b0" />
|
|
<spanspec namest="b17" nameend="b10" spanname="b1" />
|
|
<spanspec namest="b27" nameend="b20" spanname="b2" />
|
|
<spanspec namest="b37" nameend="b30" spanname="b3" />
|
|
<thead>
|
|
<row>
|
|
<entry>Identifier</entry>
|
|
<entry>Code</entry>
|
|
<entry> </entry>
|
|
<entry spanname="b0">Byte 0</entry>
|
|
</row>
|
|
<row>
|
|
<entry> </entry>
|
|
<entry> </entry>
|
|
<entry>Bit</entry>
|
|
<entry>7</entry>
|
|
<entry>6</entry>
|
|
<entry>5</entry>
|
|
<entry>4</entry>
|
|
<entry>3</entry>
|
|
<entry>2</entry>
|
|
<entry>1</entry>
|
|
<entry>0</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row id="V4L2-PIX-FMT-PAL8">
|
|
<entry><constant>V4L2_PIX_FMT_PAL8</constant></entry>
|
|
<entry>'PAL8'</entry>
|
|
<entry></entry>
|
|
<entry>i<subscript>7</subscript></entry>
|
|
<entry>i<subscript>6</subscript></entry>
|
|
<entry>i<subscript>5</subscript></entry>
|
|
<entry>i<subscript>4</subscript></entry>
|
|
<entry>i<subscript>3</subscript></entry>
|
|
<entry>i<subscript>2</subscript></entry>
|
|
<entry>i<subscript>1</subscript></entry>
|
|
<entry>i<subscript>0</subscript></entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</section>
|
|
|
|
<section id="pixfmt-rgb">
|
|
<title>RGB Formats</title>
|
|
|
|
&sub-packed-rgb;
|
|
&sub-sbggr8;
|
|
&sub-sgbrg8;
|
|
&sub-sgrbg8;
|
|
&sub-srggb8;
|
|
&sub-sbggr16;
|
|
&sub-srggb10;
|
|
&sub-srggb10p;
|
|
&sub-srggb10alaw8;
|
|
&sub-srggb10dpcm8;
|
|
&sub-srggb12;
|
|
</section>
|
|
|
|
<section id="yuv-formats">
|
|
<title>YUV Formats</title>
|
|
|
|
<para>YUV is the format native to TV broadcast and composite video
|
|
signals. It separates the brightness information (Y) from the color
|
|
information (U and V or Cb and Cr). The color information consists of
|
|
red and blue <emphasis>color difference</emphasis> signals, this way
|
|
the green component can be reconstructed by subtracting from the
|
|
brightness component. See <xref linkend="colorspaces" /> for conversion
|
|
examples. YUV was chosen because early television would only transmit
|
|
brightness information. To add color in a way compatible with existing
|
|
receivers a new signal carrier was added to transmit the color
|
|
difference signals. Secondary in the YUV format the U and V components
|
|
usually have lower resolution than the Y component. This is an analog
|
|
video compression technique taking advantage of a property of the
|
|
human visual system, being more sensitive to brightness
|
|
information.</para>
|
|
|
|
&sub-packed-yuv;
|
|
&sub-grey;
|
|
&sub-y10;
|
|
&sub-y12;
|
|
&sub-y10b;
|
|
&sub-y16;
|
|
&sub-y16-be;
|
|
&sub-y8i;
|
|
&sub-y12i;
|
|
&sub-uv8;
|
|
&sub-yuyv;
|
|
&sub-uyvy;
|
|
&sub-yvyu;
|
|
&sub-vyuy;
|
|
&sub-y41p;
|
|
&sub-yuv420;
|
|
&sub-yuv420m;
|
|
&sub-yuv422m;
|
|
&sub-yuv444m;
|
|
&sub-yuv410;
|
|
&sub-yuv422p;
|
|
&sub-yuv411p;
|
|
&sub-nv12;
|
|
&sub-nv12m;
|
|
&sub-nv12mt;
|
|
&sub-nv16;
|
|
&sub-nv16m;
|
|
&sub-nv24;
|
|
&sub-m420;
|
|
</section>
|
|
|
|
<section id="depth-formats">
|
|
<title>Depth Formats</title>
|
|
<para>Depth data provides distance to points, mapped onto the image plane
|
|
</para>
|
|
|
|
&sub-z16;
|
|
</section>
|
|
|
|
<section>
|
|
<title>Compressed Formats</title>
|
|
|
|
<table pgwide="1" frame="none" id="compressed-formats">
|
|
<title>Compressed Image Formats</title>
|
|
<tgroup cols="3" align="left">
|
|
&cs-def;
|
|
<thead>
|
|
<row>
|
|
<entry>Identifier</entry>
|
|
<entry>Code</entry>
|
|
<entry>Details</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row id="V4L2-PIX-FMT-JPEG">
|
|
<entry><constant>V4L2_PIX_FMT_JPEG</constant></entry>
|
|
<entry>'JPEG'</entry>
|
|
<entry>TBD. See also &VIDIOC-G-JPEGCOMP;,
|
|
&VIDIOC-S-JPEGCOMP;.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-MPEG">
|
|
<entry><constant>V4L2_PIX_FMT_MPEG</constant></entry>
|
|
<entry>'MPEG'</entry>
|
|
<entry>MPEG multiplexed stream. The actual format is determined by
|
|
extended control <constant>V4L2_CID_MPEG_STREAM_TYPE</constant>, see
|
|
<xref linkend="mpeg-control-id" />.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-H264">
|
|
<entry><constant>V4L2_PIX_FMT_H264</constant></entry>
|
|
<entry>'H264'</entry>
|
|
<entry>H264 video elementary stream with start codes.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-H264-NO-SC">
|
|
<entry><constant>V4L2_PIX_FMT_H264_NO_SC</constant></entry>
|
|
<entry>'AVC1'</entry>
|
|
<entry>H264 video elementary stream without start codes.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-H264-MVC">
|
|
<entry><constant>V4L2_PIX_FMT_H264_MVC</constant></entry>
|
|
<entry>'M264'</entry>
|
|
<entry>H264 MVC video elementary stream.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-H263">
|
|
<entry><constant>V4L2_PIX_FMT_H263</constant></entry>
|
|
<entry>'H263'</entry>
|
|
<entry>H263 video elementary stream.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-MPEG1">
|
|
<entry><constant>V4L2_PIX_FMT_MPEG1</constant></entry>
|
|
<entry>'MPG1'</entry>
|
|
<entry>MPEG1 video elementary stream.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-MPEG2">
|
|
<entry><constant>V4L2_PIX_FMT_MPEG2</constant></entry>
|
|
<entry>'MPG2'</entry>
|
|
<entry>MPEG2 video elementary stream.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-MPEG4">
|
|
<entry><constant>V4L2_PIX_FMT_MPEG4</constant></entry>
|
|
<entry>'MPG4'</entry>
|
|
<entry>MPEG4 video elementary stream.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-XVID">
|
|
<entry><constant>V4L2_PIX_FMT_XVID</constant></entry>
|
|
<entry>'XVID'</entry>
|
|
<entry>Xvid video elementary stream.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-VC1-ANNEX-G">
|
|
<entry><constant>V4L2_PIX_FMT_VC1_ANNEX_G</constant></entry>
|
|
<entry>'VC1G'</entry>
|
|
<entry>VC1, SMPTE 421M Annex G compliant stream.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-VC1-ANNEX-L">
|
|
<entry><constant>V4L2_PIX_FMT_VC1_ANNEX_L</constant></entry>
|
|
<entry>'VC1L'</entry>
|
|
<entry>VC1, SMPTE 421M Annex L compliant stream.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-VP8">
|
|
<entry><constant>V4L2_PIX_FMT_VP8</constant></entry>
|
|
<entry>'VP80'</entry>
|
|
<entry>VP8 video elementary stream.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</section>
|
|
|
|
<section id="sdr-formats">
|
|
<title>SDR Formats</title>
|
|
|
|
<para>These formats are used for <link linkend="sdr">SDR</link>
|
|
interface only.</para>
|
|
|
|
&sub-sdr-cu08;
|
|
&sub-sdr-cu16le;
|
|
&sub-sdr-cs08;
|
|
&sub-sdr-cs14le;
|
|
&sub-sdr-ru12le;
|
|
|
|
</section>
|
|
|
|
<section id="pixfmt-reserved">
|
|
<title>Reserved Format Identifiers</title>
|
|
|
|
<para>These formats are not defined by this specification, they
|
|
are just listed for reference and to avoid naming conflicts. If you
|
|
want to register your own format, send an e-mail to the linux-media mailing
|
|
list &v4l-ml; for inclusion in the <filename>videodev2.h</filename>
|
|
file. If you want to share your format with other developers add a
|
|
link to your documentation and send a copy to the linux-media mailing list
|
|
for inclusion in this section. If you think your format should be listed
|
|
in a standard format section please make a proposal on the linux-media mailing
|
|
list.</para>
|
|
|
|
<table pgwide="1" frame="none" id="reserved-formats">
|
|
<title>Reserved Image Formats</title>
|
|
<tgroup cols="3" align="left">
|
|
&cs-def;
|
|
<thead>
|
|
<row>
|
|
<entry>Identifier</entry>
|
|
<entry>Code</entry>
|
|
<entry>Details</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody valign="top">
|
|
<row id="V4L2-PIX-FMT-DV">
|
|
<entry><constant>V4L2_PIX_FMT_DV</constant></entry>
|
|
<entry>'dvsd'</entry>
|
|
<entry>unknown</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-ET61X251">
|
|
<entry><constant>V4L2_PIX_FMT_ET61X251</constant></entry>
|
|
<entry>'E625'</entry>
|
|
<entry>Compressed format of the ET61X251 driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-HI240">
|
|
<entry><constant>V4L2_PIX_FMT_HI240</constant></entry>
|
|
<entry>'HI24'</entry>
|
|
<entry><para>8 bit RGB format used by the BTTV driver.</para></entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-HM12">
|
|
<entry><constant>V4L2_PIX_FMT_HM12</constant></entry>
|
|
<entry>'HM12'</entry>
|
|
<entry><para>YUV 4:2:0 format used by the
|
|
IVTV driver, <ulink url="http://www.ivtvdriver.org/">
|
|
http://www.ivtvdriver.org/</ulink></para><para>The format is documented in the
|
|
kernel sources in the file <filename>Documentation/video4linux/cx2341x/README.hm12</filename>
|
|
</para></entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-CPIA1">
|
|
<entry><constant>V4L2_PIX_FMT_CPIA1</constant></entry>
|
|
<entry>'CPIA'</entry>
|
|
<entry>YUV format used by the gspca cpia1 driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-JPGL">
|
|
<entry><constant>V4L2_PIX_FMT_JPGL</constant></entry>
|
|
<entry>'JPGL'</entry>
|
|
<entry>JPEG-Light format (Pegasus Lossless JPEG)
|
|
used in Divio webcams NW 80x.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-SPCA501">
|
|
<entry><constant>V4L2_PIX_FMT_SPCA501</constant></entry>
|
|
<entry>'S501'</entry>
|
|
<entry>YUYV per line used by the gspca driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-SPCA505">
|
|
<entry><constant>V4L2_PIX_FMT_SPCA505</constant></entry>
|
|
<entry>'S505'</entry>
|
|
<entry>YYUV per line used by the gspca driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-SPCA508">
|
|
<entry><constant>V4L2_PIX_FMT_SPCA508</constant></entry>
|
|
<entry>'S508'</entry>
|
|
<entry>YUVY per line used by the gspca driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-SPCA561">
|
|
<entry><constant>V4L2_PIX_FMT_SPCA561</constant></entry>
|
|
<entry>'S561'</entry>
|
|
<entry>Compressed GBRG Bayer format used by the gspca driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-PAC207">
|
|
<entry><constant>V4L2_PIX_FMT_PAC207</constant></entry>
|
|
<entry>'P207'</entry>
|
|
<entry>Compressed BGGR Bayer format used by the gspca driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-MR97310A">
|
|
<entry><constant>V4L2_PIX_FMT_MR97310A</constant></entry>
|
|
<entry>'M310'</entry>
|
|
<entry>Compressed BGGR Bayer format used by the gspca driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-JL2005BCD">
|
|
<entry><constant>V4L2_PIX_FMT_JL2005BCD</constant></entry>
|
|
<entry>'JL20'</entry>
|
|
<entry>JPEG compressed RGGB Bayer format used by the gspca driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-OV511">
|
|
<entry><constant>V4L2_PIX_FMT_OV511</constant></entry>
|
|
<entry>'O511'</entry>
|
|
<entry>OV511 JPEG format used by the gspca driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-OV518">
|
|
<entry><constant>V4L2_PIX_FMT_OV518</constant></entry>
|
|
<entry>'O518'</entry>
|
|
<entry>OV518 JPEG format used by the gspca driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-PJPG">
|
|
<entry><constant>V4L2_PIX_FMT_PJPG</constant></entry>
|
|
<entry>'PJPG'</entry>
|
|
<entry>Pixart 73xx JPEG format used by the gspca driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-SE401">
|
|
<entry><constant>V4L2_PIX_FMT_SE401</constant></entry>
|
|
<entry>'S401'</entry>
|
|
<entry>Compressed RGB format used by the gspca se401 driver</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-SQ905C">
|
|
<entry><constant>V4L2_PIX_FMT_SQ905C</constant></entry>
|
|
<entry>'905C'</entry>
|
|
<entry>Compressed RGGB bayer format used by the gspca driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-MJPEG">
|
|
<entry><constant>V4L2_PIX_FMT_MJPEG</constant></entry>
|
|
<entry>'MJPG'</entry>
|
|
<entry>Compressed format used by the Zoran driver</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-PWC1">
|
|
<entry><constant>V4L2_PIX_FMT_PWC1</constant></entry>
|
|
<entry>'PWC1'</entry>
|
|
<entry>Compressed format of the PWC driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-PWC2">
|
|
<entry><constant>V4L2_PIX_FMT_PWC2</constant></entry>
|
|
<entry>'PWC2'</entry>
|
|
<entry>Compressed format of the PWC driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-SN9C10X">
|
|
<entry><constant>V4L2_PIX_FMT_SN9C10X</constant></entry>
|
|
<entry>'S910'</entry>
|
|
<entry>Compressed format of the SN9C102 driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-SN9C20X-I420">
|
|
<entry><constant>V4L2_PIX_FMT_SN9C20X_I420</constant></entry>
|
|
<entry>'S920'</entry>
|
|
<entry>YUV 4:2:0 format of the gspca sn9c20x driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-SN9C2028">
|
|
<entry><constant>V4L2_PIX_FMT_SN9C2028</constant></entry>
|
|
<entry>'SONX'</entry>
|
|
<entry>Compressed GBRG bayer format of the gspca sn9c2028 driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-STV0680">
|
|
<entry><constant>V4L2_PIX_FMT_STV0680</constant></entry>
|
|
<entry>'S680'</entry>
|
|
<entry>Bayer format of the gspca stv0680 driver.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-WNVA">
|
|
<entry><constant>V4L2_PIX_FMT_WNVA</constant></entry>
|
|
<entry>'WNVA'</entry>
|
|
<entry><para>Used by the Winnov Videum driver, <ulink
|
|
url="http://www.thedirks.org/winnov/">
|
|
http://www.thedirks.org/winnov/</ulink></para></entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-TM6000">
|
|
<entry><constant>V4L2_PIX_FMT_TM6000</constant></entry>
|
|
<entry>'TM60'</entry>
|
|
<entry><para>Used by Trident tm6000</para></entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-CIT-YYVYUY">
|
|
<entry><constant>V4L2_PIX_FMT_CIT_YYVYUY</constant></entry>
|
|
<entry>'CITV'</entry>
|
|
<entry><para>Used by xirlink CIT, found at IBM webcams.</para>
|
|
<para>Uses one line of Y then 1 line of VYUY</para>
|
|
</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-KONICA420">
|
|
<entry><constant>V4L2_PIX_FMT_KONICA420</constant></entry>
|
|
<entry>'KONI'</entry>
|
|
<entry><para>Used by Konica webcams.</para>
|
|
<para>YUV420 planar in blocks of 256 pixels.</para>
|
|
</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-YYUV">
|
|
<entry><constant>V4L2_PIX_FMT_YYUV</constant></entry>
|
|
<entry>'YYUV'</entry>
|
|
<entry>unknown</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-Y4">
|
|
<entry><constant>V4L2_PIX_FMT_Y4</constant></entry>
|
|
<entry>'Y04 '</entry>
|
|
<entry>Old 4-bit greyscale format. Only the most significant 4 bits of each byte are used,
|
|
the other bits are set to 0.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-Y6">
|
|
<entry><constant>V4L2_PIX_FMT_Y6</constant></entry>
|
|
<entry>'Y06 '</entry>
|
|
<entry>Old 6-bit greyscale format. Only the most significant 6 bits of each byte are used,
|
|
the other bits are set to 0.</entry>
|
|
</row>
|
|
<row id="V4L2-PIX-FMT-S5C-UYVY-JPG">
|
|
<entry><constant>V4L2_PIX_FMT_S5C_UYVY_JPG</constant></entry>
|
|
<entry>'S5CI'</entry>
|
|
<entry>Two-planar format used by Samsung S5C73MX cameras. The
|
|
first plane contains interleaved JPEG and UYVY image data, followed by meta data
|
|
in form of an array of offsets to the UYVY data blocks. The actual pointer array
|
|
follows immediately the interleaved JPEG/UYVY data, the number of entries in
|
|
this array equals the height of the UYVY image. Each entry is a 4-byte unsigned
|
|
integer in big endian order and it's an offset to a single pixel line of the
|
|
UYVY image. The first plane can start either with JPEG or UYVY data chunk. The
|
|
size of a single UYVY block equals the UYVY image's width multiplied by 2. The
|
|
size of a JPEG chunk depends on the image and can vary with each line.
|
|
<para>The second plane, at an offset of 4084 bytes, contains a 4-byte offset to
|
|
the pointer array in the first plane. This offset is followed by a 4-byte value
|
|
indicating size of the pointer array. All numbers in the second plane are also
|
|
in big endian order. Remaining data in the second plane is undefined. The
|
|
information in the second plane allows to easily find location of the pointer
|
|
array, which can be different for each frame. The size of the pointer array is
|
|
constant for given UYVY image height.</para>
|
|
<para>In order to extract UYVY and JPEG frames an application can initially set
|
|
a data pointer to the start of first plane and then add an offset from the first
|
|
entry of the pointers table. Such a pointer indicates start of an UYVY image
|
|
pixel line. Whole UYVY line can be copied to a separate buffer. These steps
|
|
should be repeated for each line, i.e. the number of entries in the pointer
|
|
array. Anything what's in between the UYVY lines is JPEG data and should be
|
|
concatenated to form the JPEG stream. </para>
|
|
</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<table frame="none" pgwide="1" id="format-flags">
|
|
<title>Format Flags</title>
|
|
<tgroup cols="3">
|
|
&cs-def;
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry><constant>V4L2_PIX_FMT_FLAG_PREMUL_ALPHA</constant></entry>
|
|
<entry>0x00000001</entry>
|
|
<entry>The color values are premultiplied by the alpha channel
|
|
value. For example, if a light blue pixel with 50% transparency was described by
|
|
RGBA values (128, 192, 255, 128), the same pixel described with premultiplied
|
|
colors would be described by RGBA values (64, 96, 128, 128) </entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</section>
|