2020-08-26 15:03:09 +08:00
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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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2018-08-30 22:15:26 +08:00
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2016-06-30 21:18:56 +08:00
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************
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Introduction
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************
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Some video capture devices can sample a subsection of a picture and
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shrink or enlarge it to an image of arbitrary size. Next, the devices
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can insert the image into larger one. Some video output devices can crop
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part of an input image, scale it up or down and insert it at an
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arbitrary scan line and horizontal offset into a video signal. We call
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these abilities cropping, scaling and composing.
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On a video *capture* device the source is a video signal, and the
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cropping target determine the area actually sampled. The sink is an
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image stored in a memory buffer. The composing area specifies which part
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of the buffer is actually written to by the hardware.
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On a video *output* device the source is an image in a memory buffer,
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and the cropping target is a part of an image to be shown on a display.
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The sink is the display or the graphics screen. The application may
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select the part of display where the image should be displayed. The size
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and position of such a window is controlled by the compose target.
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Rectangles for all cropping and composing targets are defined even if
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the device does supports neither cropping nor composing. Their size and
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position will be fixed in such a case. If the device does not support
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scaling then the cropping and composing rectangles have the same size.
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