Pixel aspect ratio
Pixel aspect ratio and engl. Pixel Aspect Ratio ( PAR ) represent the quotient of the width of a pixel (usually abbreviated x) and its height (usually abbreviated y).
The pixel aspect ratio can be determined from the ratio of the display of an image DAR (Display Aspect Ratio) (e.g. 16: 9) and the ratio of the image resolution SAR (Storage Aspect Ratio) (e.g. 1440: 1080). The general rule
Occurrence
In liquid crystal screens , the physical pixels of a panel have a square shape, i.e. each pixel (again consisting of 3 subpixels : red, green and blue) of such a screen has the same length both in width and in height and therefore has a pixel aspect ratio of 1: 1.
With plasma screens it can happen that a device with a picture surface in 16: 9 format does not have a 16: 9 resolution despite square pixels. Since the horizontal distance between the individual pixels differs from the vertical one in such cases, resolutions of 1024 × 1024 (1: 1) or 1024 × 768 (4: 3) are definitely possible.
For digital storage of PAL or NTSC according to ITU-R BT 601 , non-square pixels are used. A 4: 3 picture corresponds to a resolution of 720 × 576 (PAL) or 720 × 480 (NTSC) pixels, although typically 702 × 576 or 702 × 480 pixel images are saved (left and right are each with 9 black pixels filled in). The formats 720 × 576 and 704 × 576 (because they can be divided by 16) are permitted on video DVDs . This results in a PAR of 1.0940 (768/702) for PAL and 0.9117 (640/702) for NTSC.
The value 1.0667 is often found for PAL, which results from the reference to a width of 720 pixels (i.e. 768/720 = 16/15). This value is only correct if all 720 × 576 pixels are used for the image.
Videos can also be stored anamorphically on a DVD . A 16: 9 picture is squeezed into a 4: 3 picture, so that PARs of 1.4587 (PAL) or 1.21557 (NTSC) are created.
Pixel aspect ratio and standards
Different pixel aspect ratios apply depending on the standard used:
| PAR according to ITU-R BT-601 | PAR according to MPEG-4 | Generic PAR according to MPEG-2 | ||||
|---|---|---|---|---|---|---|
| PAL | NTSC | PAL | NTSC | PAL | NTSC | |
| 4: 3 | 1150/1053 | 38800/42651 | 12/11 | 10/11 | 16/15 | 8/9 |
| 16: 9 | 4600/3159 | 155200/127953 | 16/11 | 40/33 | 64/45 | 32/27 |
Different pixel aspect ratios
| PAR | |
|---|---|
| Square | 1 |
| D1 / DV NTSC | 0.9117 |
| D1 / DV NTSC 16: 9 anamorphic | 1.21557 |
| D1 / DV PAL | 1.0940 |
| D1 / DV PAL 16: 9 anamorphic | 1.4587 |
| Anamorphic 2: 1 | 2 |
See also
- ITU-R BT 601 (standard for digitizing analog television signals)
Web links
- Kunstuniversität Linz - Pixel Aspect Ratio About the historical creation of non-square pixels in television broadcasts; Insertion of graphics in video projects taking into account different pixel aspect ratios
- The importance of the ITU-R BT.601 for the PAR