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