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1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later2 3************4Introduction5************6 7Some video capture devices can sample a subsection of a picture and8shrink or enlarge it to an image of arbitrary size. Next, the devices9can insert the image into larger one. Some video output devices can crop10part of an input image, scale it up or down and insert it at an11arbitrary scan line and horizontal offset into a video signal. We call12these abilities cropping, scaling and composing.13 14On a video *capture* device the source is a video signal, and the15cropping target determine the area actually sampled. The sink is an16image stored in a memory buffer. The composing area specifies which part17of the buffer is actually written to by the hardware.18 19On a video *output* device the source is an image in a memory buffer,20and the cropping target is a part of an image to be shown on a display.21The sink is the display or the graphics screen. The application may22select the part of display where the image should be displayed. The size23and position of such a window is controlled by the compose target.24 25Rectangles for all cropping and composing targets are defined even if26the device does supports neither cropping nor composing. Their size and27position will be fixed in such a case. If the device does not support28scaling then the cropping and composing rectangles have the same size.29