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## What is the "Sub pixel accuracy" ?

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### #1SPR  Members

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Posted 08 October 1999 - 09:53 AM

Hi everybody !

I'm not sure that I'm in the correct place, but I can't find better place to ask it.
So I've read somewhere about the "Sub pixel accuracy". The article said,that with this, smooth movement can be implemented in a polygon based word. There wasn't any explanation ,or theory or code in the article.
So I would like to ask what is the Sub pixel accuracy, how can it be implemented, what is its theory.

Thanks !

### #2SonicSilcion  Members

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Posted 07 October 1999 - 04:47 AM

__Basically it's a fancy term for how well rendered polygons are anti-aliased (smooth edged.) "Sub pixel" refers to the rendering resolution (as opposed to the display resolution) of graphics.
__The accuracy of is often stated as a ratio of the two resolutions (rendered:displayed.) For example, a scene is rendered at 640x400 and is downsampled (squished) to fit on a 320x200 display. The accuracy would be 2:1 (sometimes stated as 2x.) In this example, the rendering time would be quadrupled! =(
__However, we're talking about polygons. The rendering time doesn't need to be that long. All that needs to be done is a sub-sampling of the lines constructing the polygons. Basically, instead of taking the interger of the calculated result (of y=x*slope), you split the value in to two parts: a bottom value (botValue = value - int(value)) and a top value (topValue = value - botValue). All that's left is adding (the new values multiplyed by the color of the line) to (the value of the current pixel * (100%-value)) and voila! Anti-aliased lines (of course someone else, probably could explain this better :} )
__I hope this helped!

### #3FlyFire  Members

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Posted 07 October 1999 - 06:55 AM

Check out Chris Hecker's texture mapper tutorial where sub-pixel and sub-texel accuracy very good explained
http://www.d6.com/users/checker/misctech.htm

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FlyFire/CodeX
http://codexorg.webjump.com

### #4erich  Members

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Posted 08 October 1999 - 09:53 AM

You might also want to check out the article on this very site on this topic: http://www.gamedev.net/reference/programming/graphics3d/article661.asp

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