Am 29.08.2012 07:42, schrieb Ive:

> But what I will try some day is using POV-Ray as spectral renderer :)
>
> This could be done within an animation loop of e.g. 31 steps in 10nm
> from 400nm to 700nm (I got inspired by Bruce Lindbloom who did exactly
> this with his own self-made renderer).

11 steps will do if you make use of three color channels per frame :)

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Le 29/08/2012 12:08, clipka a écrit :
> Am 29.08.2012 07:42, schrieb Ive:
> 
>> But what I will try some day is using POV-Ray as spectral renderer :)
> 
> And what /I/ will do some day is make a spectral rendering patch for
> POV-Ray :-)
> 
> From a mathematical point of view, the classic three-component RGB
> approach is a pretty poor one, no matter what color space you're using.
> From all the brain-wrecking I did about the topic, I suspect that a
> straightforward N-channel spectral approach is the best solution.
> 
> But first there's some cleaning-up to do on the color handling code of
> official POV-Ray.
> 


Assuming a ray's color is a 1D vector spectrum, please make the
pigment's color a 2D matrix. Most matrix would be resumed to a diagonal,
but using a matrix would allow to model shift on the spectrum.

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Am 29.08.2012 12:11, schrieb clipka:
> Am 29.08.2012 07:42, schrieb Ive:
> 11 steps will do if you make use of three color channels per frame :)

Of course [heading my forehead with my fist] thats brilliant. With only 
11 animation frames a range from lets say 380nm to 700nm can be covered.

BTW I'm aware that POV-Ray internally assumes sRGB primaries for 
iridescence and color->grayscale conversion. Is there anything else 
internally hard-coded that expects sRGB?

-Ive

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Am 29.08.2012 12:08, schrieb clipka:
> Am 29.08.2012 07:42, schrieb Ive:
>
>> But what I will try some day is using POV-Ray as spectral renderer :)
>
> And what /I/ will do some day is make a spectral rendering patch for
> POV-Ray :-)
>
>  From a mathematical point of view, the classic three-component RGB
> approach is a pretty poor one, no matter what color space you're using.
>  From all the brain-wrecking I did about the topic, I suspect that a
> straightforward N-channel spectral approach is the best solution.
>
Do you really think this is worth the effort? To really benefit from a 
spectral render engine one needs spectral data for diffuse and specular 
reflectance for A LOT of materials. But somehow I suspect not that many 
POV-Ray users have a spectrophotometer at home.


> But first there's some cleaning-up to do on the color handling code of
> official POV-Ray.
>
Like what? Just curious.

-Ive

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Am 29.08.2012 09:13, schrieb Jaime Vives Piqueres:
> Darn... I was expecting a yellow Dogde Challenger! :)
>
As usual I'm just hopping from one unfinished project to the next!
My virtue of patience is not as strong as you might think ;)

And this actually reminds me of some beauty line named in your honor 
that needs my attention... *

-Ive

* sorry: in-joke

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In case anyone is interested, I have made a 1920x1200 16bit/channel PNG 
version and also the "raw" rendered data in linear Adobe-RGB as a TIFF 
available from my side at
http://www.lilysoft.org/CGI/YMO/yellowmagic.htm
But be warned, those are big files.

-Ive

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Am 29.08.2012 10:08, schrieb Thomas de Groot:
> This going a bit beyond my mental capacities, but I find it fascinating
> nonetheless. ;-)
>
Well, I'm not good in explaining, but all this is just about that within 
the sRGB color space "only" 35% of the colors an average can "see" and 
distinguish are represented. Within Adobe RGB this is already about 50% 
and lets say a high quality art print covers up to 90%.

In practice the 35% of sRGB are not as bad as it sounds as mainly 
high-saturated colors are effected and as long as nobody opens a 
New-Wave nightclub in Gancaloon it shouldn't be much of a problem ;)

-Ive

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Am 29.08.2012 13:33, schrieb Ive:
> an average can "see" and

err, make this "an average human can "see" and" ...

-Ive

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Am 29.08.2012 13:12, schrieb Ive:
> Am 29.08.2012 12:08, schrieb clipka:
>> Am 29.08.2012 07:42, schrieb Ive:
>>
>>> But what I will try some day is using POV-Ray as spectral renderer :)
>>
>> And what /I/ will do some day is make a spectral rendering patch for
>> POV-Ray :-)
>>
>>  From a mathematical point of view, the classic three-component RGB
>> approach is a pretty poor one, no matter what color space you're using.
>>  From all the brain-wrecking I did about the topic, I suspect that a
>> straightforward N-channel spectral approach is the best solution.
>>
> Do you really think this is worth the effort?

I won't know until I try :-)

> To really benefit from a
> spectral render engine one needs spectral data for diffuse and specular
> reflectance for A LOT of materials. But somehow I suspect not that many
> POV-Ray users have a spectrophotometer at home.

While that's certainly true, I guess even with rgb-specified colors it 
will already do some good to scenes with colored transparent objects, so 
that e.g. two orange filters in sequence won't necessarily exhibit a hue 
shift towards red, but could retain the orange hue while just gaining in 
saturation.

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Am 29.08.2012 13:12, schrieb Ive:

>> But first there's some cleaning-up to do on the color handling code of
>> official POV-Ray.
>>
> Like what? Just curious.

Using the same color data type throughout, for instance. As it is now, 
some parts of the code use old C-style structures, while others already 
use C++-style objects. Obviously, a consistent use of C++-style objects 
would be easier to base a spectral rendering patch on.

Another thing is the internal handling of F and T components, which I 
intend to replace with a full RGB transparency model. Again, this will 
simplify implementing a sane spectral rendering patch.

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