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fstops and 8 bit RGB colour space


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#1 c_conditt

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Posted 05 April 2007 - 05:41 PM

Basically, is it true, that a monitor with 256 shades of each color, can display 8 stops?

if one stop is double the amount of light, does the following calculation make sense?

1,2,4,8,16,32,64,128,256

gives us 8 stops..


the thing is, i tried that out in photoshop - but it completely does not work out.

the shades from 1 to 32 are almost indstinguishable, and the last steps dont feel like natural stops neither..


where is my error?

THANKSALOT!
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#2 Walter Graff

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Posted 05 April 2007 - 06:14 PM

Partially because your gamma settings on your monitor will affect how well you can see differences in gray values. If your monitor is properly set up you should see such a scale more evenly. The mathematics of color depth and the perception of how it looks are sometimes two different tings similar to the discussion of 720 and 1080 in that it's more about perception than simply numbers. It's one of the reasons why we really don't need incredible bit depth to see a picture represented well on a computer monitor.
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#3 Graeme Nattress

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Posted 05 April 2007 - 07:09 PM

Walter, you hit the nail on the head. The magic word is "gamma". This is a non-linearity in the signal that is corrected by a non-linearity in a CRT display (and faked in LCD) that allows for a greater dynamic range than 8 stops to be represented by 8bit data, among other things. I'd check out Poynton's Gamma FAQ for more info. www.poynton.com

Graeme
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