1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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4 Introduction 4 Introduction
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7 Some video capture devices can sample a subsec 7 Some video capture devices can sample a subsection of a picture and
8 shrink or enlarge it to an image of arbitrary 8 shrink or enlarge it to an image of arbitrary size. Next, the devices
9 can insert the image into larger one. Some vid 9 can insert the image into larger one. Some video output devices can crop
10 part of an input image, scale it up or down an 10 part of an input image, scale it up or down and insert it at an
11 arbitrary scan line and horizontal offset into 11 arbitrary scan line and horizontal offset into a video signal. We call
12 these abilities cropping, scaling and composin 12 these abilities cropping, scaling and composing.
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14 On a video *capture* device the source is a vi 14 On a video *capture* device the source is a video signal, and the
15 cropping target determine the area actually sa 15 cropping target determine the area actually sampled. The sink is an
16 image stored in a memory buffer. The composing 16 image stored in a memory buffer. The composing area specifies which part
17 of the buffer is actually written to by the ha 17 of the buffer is actually written to by the hardware.
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19 On a video *output* device the source is an im 19 On a video *output* device the source is an image in a memory buffer,
20 and the cropping target is a part of an image 20 and the cropping target is a part of an image to be shown on a display.
21 The sink is the display or the graphics screen 21 The sink is the display or the graphics screen. The application may
22 select the part of display where the image sho 22 select the part of display where the image should be displayed. The size
23 and position of such a window is controlled by 23 and position of such a window is controlled by the compose target.
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25 Rectangles for all cropping and composing targ 25 Rectangles for all cropping and composing targets are defined even if
26 the device does supports neither cropping nor 26 the device does supports neither cropping nor composing. Their size and
27 position will be fixed in such a case. If the 27 position will be fixed in such a case. If the device does not support
28 scaling then the cropping and composing rectan 28 scaling then the cropping and composing rectangles have the same size.
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