Video aspect ratio and Pixel aspect ratio

[LeoKac]

I know what "Video aspect ratio" is, and i know what "Pixel aspect ratio" is too, but I can't understand why "Pixel aspect ratio" is needed? There are many TVs that have not 1.000 "Pixel aspect ratio", they have stretched pixels instead of square pixels. non-square pixels represent image stretched and ugly, disfigured. (I hate stretched and non-natural images)

Well, I think that only video aspect ratio is needed for image presentation, and pixel must be necessarily square. what would you say about it?
thanks...

[DB83]

If you really knew what they were, you would not post such rubbish.

Non-square pixels only exist AFAIK for dvd-playback. They are there to ensure that your 720*576 pixels correctly display for either a 4:3 image or a 16:9 image.

The stretching that you refer to is probably the result of not displaying a 4:3 image as 4:3. People do not like the left/right borders so 'stretch' to compensate and 'fill' the screen'.

[intracube]

Well, I think that only video aspect ratio is needed for image presentation, and pixel must be necessarily square. what would you say about it?
thanks...

What you say is incorrect. Non-square pixels are used in most SD digital video standards and even for HD on occasion.

You're confusing badly set up televisions with pixel aspect ratio.

Take a typical example; 720x576 16:9 SD video. If you get out a calculator you'll see that 720x576 won't give a 16:9 image (assuming square pixels). That's because the pixels aren't square. They need to be stretched horizontally to get a 16:9 image with the correct proportions.

You can ask why 720x576 is used instead of 1024x576 (which would be 16:9 square pixel) - that would be a valid question.

[intracube]

More info:
http://forum.videohelp.com/threads/323530-please-explain-SAR-DAR-PAR

A simplistic overview; A standard definition camera creates a 16:9 video which then gets distorted/squashed to fit a 720x576 frame. This gets transmitted digitally on satellite, cable or stored on DVD. Then when the video is viewed, a TV should see the embedded aspect ratio information and un-distort the video to the correct proportions. It's at this point that the pixels effectively get stretched and become rectangular.