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<small>[http://www.labdv.com/learning/dv_basics/aspect_ratio-en.html 3. Digital video : the pixel ratio]The legacy digital representation of computer 4:3 NTSC has a format of 640x480 pixels. This is a natural choice, if you consider that 480 lines makes 480 pixels vertically, and 4:3 aspect makes 480 x 4/3 = 640 pixels horizontally. However, DV cameras as well as most digital video equipment work with a 720x480 frame size. Therefore, if you considered your picture elements to have a square aspect ratio (1:1) in analog format, your digitised frame now has a pixel ratio of 0.888 (640/720). You can view it that way: it takes 720 pixels with a 0.88 ratio to equate 640 pixels with a 1.00 ratio. Following the same idea, 16:9 NTSC has a pixel ratio of 1.20 (864/720). The "864" value comes from taking 460 x 16/9 = 853.3 and rounding to 864, since any line must have a number of pixels that can be divided by 16.This mismatch between analog and digital pixel ratios, present on most equipment, requires some precautions be taken if one wants to preserve the exact aspect ratio of images. Circles on TV appear like ellipses on a computer screen and vice-versa! To illustrate the problem, consider the following example: you want to scan some photographs and transfer them to stills in DV format. If you're thinking of just scanning the images and resize to 720x480 (DV frame size), you're wrong. You must first crop the images to a 4:3 aspect ratio, then resize them, which will stretch them a little, but this way, they will appear correct on your TV !</small>