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| -rw-r--r-- | Documentation/userspace-api/media/v4l/selection-api-intro.rst | 28 |
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diff --git a/Documentation/userspace-api/media/v4l/selection-api-intro.rst b/Documentation/userspace-api/media/v4l/selection-api-intro.rst new file mode 100644 index 000000000..6534854ae --- /dev/null +++ b/Documentation/userspace-api/media/v4l/selection-api-intro.rst @@ -0,0 +1,28 @@ +.. 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. |