| .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later | |
| .. c:namespace:: V4L | |
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| Introduction | |
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| 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. |