1*4882a593Smuzhiyun.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2*4882a593Smuzhiyun 3*4882a593Smuzhiyun************ 4*4882a593SmuzhiyunIntroduction 5*4882a593Smuzhiyun************ 6*4882a593Smuzhiyun 7*4882a593SmuzhiyunSome video capture devices can sample a subsection of a picture and 8*4882a593Smuzhiyunshrink or enlarge it to an image of arbitrary size. Next, the devices 9*4882a593Smuzhiyuncan insert the image into larger one. Some video output devices can crop 10*4882a593Smuzhiyunpart of an input image, scale it up or down and insert it at an 11*4882a593Smuzhiyunarbitrary scan line and horizontal offset into a video signal. We call 12*4882a593Smuzhiyunthese abilities cropping, scaling and composing. 13*4882a593Smuzhiyun 14*4882a593SmuzhiyunOn a video *capture* device the source is a video signal, and the 15*4882a593Smuzhiyuncropping target determine the area actually sampled. The sink is an 16*4882a593Smuzhiyunimage stored in a memory buffer. The composing area specifies which part 17*4882a593Smuzhiyunof the buffer is actually written to by the hardware. 18*4882a593Smuzhiyun 19*4882a593SmuzhiyunOn a video *output* device the source is an image in a memory buffer, 20*4882a593Smuzhiyunand the cropping target is a part of an image to be shown on a display. 21*4882a593SmuzhiyunThe sink is the display or the graphics screen. The application may 22*4882a593Smuzhiyunselect the part of display where the image should be displayed. The size 23*4882a593Smuzhiyunand position of such a window is controlled by the compose target. 24*4882a593Smuzhiyun 25*4882a593SmuzhiyunRectangles for all cropping and composing targets are defined even if 26*4882a593Smuzhiyunthe device does supports neither cropping nor composing. Their size and 27*4882a593Smuzhiyunposition will be fixed in such a case. If the device does not support 28*4882a593Smuzhiyunscaling then the cropping and composing rectangles have the same size. 29