0001 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
0002
0003 ************
0004 Introduction
0005 ************
0006
0007 Some video capture devices can sample a subsection of a picture and
0008 shrink or enlarge it to an image of arbitrary size. Next, the devices
0009 can insert the image into larger one. Some video output devices can crop
0010 part of an input image, scale it up or down and insert it at an
0011 arbitrary scan line and horizontal offset into a video signal. We call
0012 these abilities cropping, scaling and composing.
0013
0014 On a video *capture* device the source is a video signal, and the
0015 cropping target determine the area actually sampled. The sink is an
0016 image stored in a memory buffer. The composing area specifies which part
0017 of the buffer is actually written to by the hardware.
0018
0019 On a video *output* device the source is an image in a memory buffer,
0020 and the cropping target is a part of an image to be shown on a display.
0021 The sink is the display or the graphics screen. The application may
0022 select the part of display where the image should be displayed. The size
0023 and position of such a window is controlled by the compose target.
0024
0025 Rectangles for all cropping and composing targets are defined even if
0026 the device does supports neither cropping nor composing. Their size and
0027 position will be fixed in such a case. If the device does not support
0028 scaling then the cropping and composing rectangles have the same size.
