| Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 1 | .. -*- coding: utf-8; mode: rst -*- |
| 2 | |
| 3 | ************ |
| 4 | Introduction |
| 5 | ************ |
| 6 | |
| 7 | Some video capture devices can sample a subsection of a picture and |
| 8 | shrink or enlarge it to an image of arbitrary size. Next, the devices |
| 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 and insert it at an |
| 11 | arbitrary scan line and horizontal offset into a video signal. We call |
| 12 | these abilities cropping, scaling and composing. |
| 13 | |
| 14 | On a video *capture* device the source is a video signal, and the |
| 15 | cropping target determine the area actually sampled. The sink is an |
| 16 | image stored in a memory buffer. The composing area specifies which part |
| 17 | of the buffer is actually written to by the hardware. |
| 18 | |
| 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 to be shown on a display. |
| 21 | The sink is the display or the graphics screen. The application may |
| 22 | select the part of display where the image should be displayed. The size |
| 23 | and position of such a window is controlled by the compose target. |
| 24 | |
| 25 | Rectangles for all cropping and composing targets are defined even if |
| 26 | the device does supports neither cropping nor composing. Their size and |
| 27 | position will be fixed in such a case. If the device does not support |
| 28 | scaling then the cropping and composing rectangles have the same size. |