### Monday, December 26, 2005

## Request For Comment

I've been pondering on a method of scaling down video under a certain number of overall pixels while maintaining aspect ratio. I came up with this:

width = sqrt(pixels * aspect)

height = sqrt(pixels / aspect)

So far that seems to work rather nicely. Is this correct, or is there a better way?

width = sqrt(pixels * aspect)

height = sqrt(pixels / aspect)

So far that seems to work rather nicely. Is this correct, or is there a better way?

Comments:

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pixels = width * height

aspect = width / height

width = sqrt(pixels * aspect)

= sqrt((width * height) * (width / height))

= sqrt(witdth * width * height / height)

= sqrt(width^2)

= width

height = sqrt(pixels / aspect)

= sqrt((width * height) / (width / height))

= sqrt(height^2)

= height

So your equations are certainly true. And if you have both the number of pixels and the aspect ratio handy, and don't mind doing a square root, then it doesn't seem too bad. I can't claim for certain that there's no better way though.

Peter McCurdy.

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aspect = width / height

width = sqrt(pixels * aspect)

= sqrt((width * height) * (width / height))

= sqrt(witdth * width * height / height)

= sqrt(width^2)

= width

height = sqrt(pixels / aspect)

= sqrt((width * height) / (width / height))

= sqrt(height^2)

= height

So your equations are certainly true. And if you have both the number of pixels and the aspect ratio handy, and don't mind doing a square root, then it doesn't seem too bad. I can't claim for certain that there's no better way though.

Peter McCurdy.

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