The problem you're all running into is with the coloured lights... They WILL
not convert, no matter what you do, because coloured lights cause the
diffuse and specular areas of objects to have different exposures.

The problem is not with gamma.

Try this for me, place a shiny yellow sphere in a scene with a red light on
the left side, a green light at the camera and a blue light on the right
side.

Because of the coloured lights, you can't simulate the picture using the
"converted pigments" method.  The colour version when converted to greyscale
is nothing like the "converted pigments" version because the colour
version's lights affect the exposure of the surface of the sphere, where the
converted pigments method doesn't because all the lights are really just
intensities of white.

See?

--
Lance.


---
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Spider wrote in message <36EC07D4.48E05A0B@bahnhof.se>...
>
>
>Bob Hughes wrote:
>>
>> I converted your image to grayscale using Micrografx Picture Publisher
>> and it really shows the changes from one to the other. The "red shadow"
>> I mentioned before, I think this is actually a reddish hemisphere
>> instead, it obviously loses the dark to light shading it had in the
>> color image in your example. When the whole thing is converted via P.P.
>> it remains shaded properly as expected. And that color image with the
>> all-blue box at the spheres equator is a puzzle to me. It has no
>> shading, then in the macro-converted grayscale it does?! Strange. That's
>> what I was pointing out before.
>
>Yes, I know it's not perfect, but I think it's fairly good, esp. if there
is no
>original.. I don't have the time to tweak it here, you could if you like,
but
>noone is forcing you. :-)
>(see below for the shading question.)
>
>> So you think there are other conversion formulas possible? I see you
>> used the one in the POV-Ray DOC under hf_gray_16 output. Wonder why this
>> wouldn't already be right?
>
>I think it's because there is no gamma-correction done on that. I think the
>gamma is based on the colour of the image, no?  and that is the difference.
>
>
>--
>//Spider
>( spi### [at] bahnhofse ) [ http://www.bahnhof.se/~spider/ ]
>#declare life = rand(seed(42))*sqrt(-1);

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