In article <web.3ecf8a69a14066c984d065310@news.povray.org>,
 "Matti Karnaattu" <nomail@nomail> wrote:

> Photographers use gray surface which reflects 18% light back to make
> adjustments because it looks half bright.
> 
>   0.18^x = 0.5
> 
>   x = ln(0.5)/ln(0.18)
> 
> I'm not sure about this gamma. I'm still looking more information about
> simulating camera and human eye dynamic range.

The gamma is an approximation to the non-linear response curve of CRT 
phosphors: 50% gray is neither 50% intensity nor 50% apparent intensity. 
Gamma currection compensates for this to give a nearly linear response. 
(LCD's have an S-shaped curve, probably based on cosine, but modern LCD 
displays probably compensate for this electronically.)

I don't know if a logarithmic scale would be useful given the limited 
dynamic range of monitors and typical depth resolutions (usually 8 bits 
per component, for 255 non-black levels). Also, people who work with 
color learn to use linear values, they would have to re-learn everything 
to use a logarithmic color space. It isn't more "correct", it is just a 
different system.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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