POV-Ray : Newsgroups : povray.binaries.images : Friday abstract: spectral subtractive color mixing Server Time: 18 Aug 2017 05:04:02 GMT
 Friday abstract: spectral subtractive color mixing (Message 1 to 5 of 5)
 From: Cousin Ricky Subject: Friday abstract: spectral subtractive color mixing Date: 18 Nov 2016 16:36:44 Message: <582f2e1c@news.povray.org>
```These four images are all rendered spectrally.

Image subtractive-arith.jpg uses straightforward arithmetic averaging of
4 colors.  Clearly, arithmetic averaging is not the way to simulate the
mixing of pigments.

Images subtractive_blob-k.jpg and subtractive_blob-w.jpg use geometric
averaging of 4 colors.

Image subtractive_blob-cmy.jpg uses geometric averaging of 3 colors.
```

Attachments:

Preview of image 'subtractive-arith.jpg'

Preview of image 'subtractive_blob-k.jpg'

Preview of image 'subtractive_blob-w.jpg'

Preview of image 'subtractive_blob-cmy.jpg'

 From: clipka Subject: Re: Friday abstract: spectral subtractive color mixing Date: 18 Nov 2016 17:11:50 Message: <582f3656\$1@news.povray.org>
```Am 18.11.2016 um 17:38 schrieb Cousin Ricky:
> These four images are all rendered spectrally.
>
> Image subtractive-arith.jpg uses straightforward arithmetic averaging of
> 4 colors.  Clearly, arithmetic averaging is not the way to simulate the
> mixing of pigments.

algorithm:

- For each colour involved, compute its luminance.

- For each colour, compute the lightness from the luminance.
- Compute the arithmetic average of all the lightness values.
- Compute the result luminance from the averaged lightness.

- For each colour involved, normalize it to unity luminance
by dividing each component by the colour's computed luminance.
- Compute the arithmetic average of the normalized colours.

- Renormalize the result colour to the result luminance
by multiplying each component with the result luminance.

POV-Ray 3.7.1 supports this type of averaging in pigment maps and colour
maps, using "blend_mode 3" (IIRC); by default, it uses Y=V^2.4 as the
formula to convert between luminance (Y) and lightness (V).
```
 From: Cousin Ricky Subject: Re: Friday abstract: spectral subtractive color mixing Date: 18 Nov 2016 18:15:01 Message:
```clipka <ano### [at] anonymousorg> wrote:
> algorithm:
>
>   - For each colour involved, compute its luminance.
>
>   - For each colour, compute the lightness from the luminance.
>   - Compute the arithmetic average of all the lightness values.
>   - Compute the result luminance from the averaged lightness.
>
>   - For each colour involved, normalize it to unity luminance
>     by dividing each component by the colour's computed luminance.
>   - Compute the arithmetic average of the normalized colours.
>
>   - Renormalize the result colour to the result luminance
>     by multiplying each component with the result luminance.

Does this work with spectral rendering?
```
 From: clipka Subject: Re: Friday abstract: spectral subtractive color mixing Date: 18 Nov 2016 18:27:46 Message: <582f4822\$1@news.povray.org>
```Am 18.11.2016 um 19:13 schrieb Cousin Ricky:
> clipka <ano### [at] anonymousorg> wrote:
>> algorithm:
>>
>>   - For each colour involved, compute its luminance.
>>
>>   - For each colour, compute the lightness from the luminance.
>>   - Compute the arithmetic average of all the lightness values.
>>   - Compute the result luminance from the averaged lightness.
>>
>>   - For each colour involved, normalize it to unity luminance
>>     by dividing each component by the colour's computed luminance.
>>   - Compute the arithmetic average of the normalized colours.
>>
>>   - Renormalize the result colour to the result luminance
>>     by multiplying each component with the result luminance.
>
> Does this work with spectral rendering?

If you can compute the luminance of a colour across all channels that
will eventually be rendered, then yeah -- that should certainly work.
```
 From: Paolo Gibellini Subject: Re: Friday abstract: spectral subtractive color mixing Date: 21 Nov 2016 12:32:18 Message: <5832e952\$1@news.povray.org>
```Cousin Ricky wrote on 18/11/2016 17:38:
> These four images are all rendered spectrally.
>
> Image subtractive-arith.jpg uses straightforward arithmetic averaging of
> 4 colors.  Clearly, arithmetic averaging is not the way to simulate the
> mixing of pigments.
>
> Images subtractive_blob-k.jpg and subtractive_blob-w.jpg use geometric
> averaging of 4 colors.
>
> Image subtractive_blob-cmy.jpg uses geometric averaging of 3 colors.

Lovely!
Paolo
```