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  1. Member
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    Wiki defines Aspect Ratio as width divided by height. I understand that but I’m confused on how aspect ratio affects resolution or visa versa. For example: A standard NTSC DVD has a resolution of 720x480 and an aspect ratio of 16:9 or 4:3. Now neither 16:9 nor 4:3 divide out to 1.5 (720/480 or w/h). Is there something I’m missing here?
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  2. Going Mad TheFamilyMan's Avatar
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    Short answer: In TV land, the pixels aren't squares.

    Long answer: A TV pictures is based on horizontal scan lines, which is were 480 comes from. Each scan line is actually a row of dots, which is where the 720 comes from. The 3x4 comes from what the old movies used for their screen aspect. Beyond that there is nothing special about it. Same goes for 16x9, though I'm not sure why they picked that ratio since most wide screen films are somewhat wider.
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  3. Member
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    Ok I think I got it now. So resolution is physical count of horizontal and vertical rows while aspect ratio is header information used to tell the playback device how the video should be displayed on a screen?
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  4. Member Krispy Kritter's Avatar
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    There are also definitions on this site. Just see WHAT IS : GLOSSARY in the upper left.
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  5. Human j1d10t's Avatar
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    Check out this guide on AR and resolutions:
    https://forum.videohelp.com/topic174200.html

    Very detailed, and well worth the read.
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  6. Member Alex_ander's Avatar
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    Originally Posted by slmnow
    Ok I think I got it now. So resolution is physical count of horizontal and vertical rows while aspect ratio is header information used to tell the playback device how the video should be displayed on a screen?
    Absolutely right. As mentioned, vertical numbers for digital storage were taken in compatibility with analog TV standard (totally 525 lines, 480 displayed, the rest blanked to allow for the deflecting beam in camera/display electron tube to return). In horizontal direction the size can be easily changed on analog display (it's continuous horizontally though discrete vertically) and this allows to encode 4:3 and 16:9 pictures using the same storage matrix + AR flag. There is no such a thing in reality as widely used 'square or non-square pixels', it's an imaginary thing reminding whether or not you can use pixel numbers to directly read AR. And there are no pixels at all in analog TV signal.
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  7. 16:9 and 4:3 are Display Aspect Ratios (DAR), not quite the same thing. Say you have a "fullscreen" AVI. It may have a resolution of 512x384, or 576x432, or 640x480 (or others). They're all the same Aspect Ratio. They're all 1.33:1. But they're different resolutions.

    As you said, a 720x480 DVD VOB has an Aspect Ratio of 1.5:1. If you've ever looked at a VOB before it's resized, you'll realize things don't look "normal". People are stretched or squashed. It has to be resized properly. That's where the DAR comes in. It tells the player how it's to be resized. If 4:3, it becomes 640x480 when resized (480 x (4/3) = 640). If the DAR is 16:9, when that VOB is resized it becomes roughly 854x480 (480 x (16/9) = 853.33x480).
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  8. Member edDV's Avatar
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    At popular HD production/transmission resolutions 1280x720 and 1920x1080, pixels are square and aspect ratio is 16:9. Displays vary in resolution from ~1024x768 through 1366x768, 1440x1080 to 1920x1080.

    For 1366x768 and 1920x1080 pixels are approximately square. You would think 1920x1080 results in a pixel by pixel mapping for 1920x1080i but no. The TV industry almost always overscans the display 3-10% for a variety of valid reasons.
    http://en.wikipedia.org/wiki/Overscan

    So even where transmission resolution matches display resolution, the image is scaled in H and V for display.

    1024x768 and 1440x1080 produce a 4:3 aspect ratio with square pixels but instead 4:3 aspect (1.33 PAR) pixels are used to stretch these display resolutions over a 16:9 display. This may seem strange but is common for plasma displays.

    Before you start feeling "resolution cheated" at 1440x1080, realize that most all broadcast tape recording formats store 1440x1080 pixels (HDV, XDCAM, HDCAM) or less (DVCPRO uses 1280x1080 or 960x720).

    Just relax and enjoy the pretty pictures.
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  9. DAR = PAR * SAR

    DAR = display aspect ratio, the relative dimensions the video should be displayed at.
    PAR = pixel aspect ratio, the relative dimensions of individual pixels.
    SAR = storage aspect ratio, the frame dimensions in number of pixels.

    In the computer video world resolution has come to mean the same thing as SAR.
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