>High!
>
>Mike Williams wrote:
>
>> For non-grey colours, the albedo is probably best represented by
>>.gray  (watch out for that American spelling, the UK English spelling
>>doesn't  work) which returns a value where the three components are
>>weighted in a  way that corresponds to the way the human eye responds.
>
>Is the .gray value equivalent to the luminosity value in the HSL model?
>I just started an animation of the Jovian moon Amalthea (albedo 0.09)
>using the CHSL2RGB macro in colors.inc...

No, they're very different.

color.gray responds in the same way as the pigments in the human eye.
The eye is more sensitive to green and less sensitive to blue. I believe
that the calculation is

   gray = R*0.297 + G*0.569 + B*0.114

The L in HSL is calculated using only two colours, the ones that have
the max and min values in RGB space:

   L = (max + min)/2

   pure red   gives gray=0.297 L=0.5
   pure green gives gray=0.569 L=0.5
   pure blue  gives gray=0.114 L=0.5

-- 
Mike Williams
Gentleman of Leisure

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