Pixel Aspect Ratio
Television signals are transmitted in digital form, and their pixels have a rectangular shape, as opposed to square pixels that are used in modern computer monitors and modern implementations of HDTV. The table below summarizes pixel aspect ratios for various kinds of SDTV video signal. Note that the actual image (be it 4:3 or 16:9) is always contained in the center 704 horizontal pixels of the digital frame, regardless of how many horizontal pixels (704 or 720) are used. In case of digital video signal having 720 horizontal pixels, only the center 704 pixels contain actual 4:3 or 16:9 image, and the 8 pixel wide stripes from either side are called nominal analogue blanking and should be discarded before displaying the image. Nominal analogue blanking should not be confused with overscan, as overscan areas are part of the actual 4:3 or 16:9 image.
| Video Format | Resolution | Pixel Aspect Ratio | Equivalent square-pixel resolution |
|---|---|---|---|
| 576i 4:3 | 704×576 | 12:11 | 768×576 |
| 720×576 | 786×576 | ||
| 576i 16:9 | 704×576 | 16:11 | 1024×576 |
| 720×576 | 1048×576 | ||
| 480i 4:3 | 704×480 | 10:11 | 640×480 |
| 720×480 | 654×480 | ||
| 480i 16:9 | 704×480 | 40:33 | 854×480 |
| 720×480 | 872×480 |
The pixel aspect ratio is always the same for corresponding 720 and 704 pixel resolutions because the center part of a 720 pixels wide image is equal to the corresponding 704 pixels wide image.
Read more about this topic: Standard-definition Television
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