"SharkD" <mik### [at] gmailcom> schreef in bericht 
news:4b0eec8a$1@news.povray.org...
> That's a very interesting idea. I might try and create such a tool.
>

and then in sRGB space?

Thomas

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El 26/11/09 22:01, SharkD escribió:
> That's a very interesting idea. I might try and create such a tool.
>

   I just found an online tool that could be used as inspiration:

   http://javascript.about.com/library/blpaint4.htm

   Regards,


-- 
Jaime Vives Piqueres

http://www.ignorancia.org

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Thanks for the reactions

@Jaime: that makes it a lot easier, indeed, hadn't thought that was possible.
I'm going to experiment with that.

@Michael: I'll be waiting in anticipation... ;-)

Grtz, Joost

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joost_1972 wrote:
> Hi,
> 
> I was wondering if anybody could help me to a color mixing tool? I've found
> enough color pickers with all kind of options, but non with the same options you
> have in real life. When I have a certain color I often just want to add a hint
> of an other color, as I do with painting, but can find it quite hard to get the
> right touch with the numbers.
> 
> Thanks, Joost

Sometimes when I need a real-life color, I will open a photo with 
IrfanView and click on the color I want, to read the RGB values. I take 
those values and convert them in POV like so:

rgb <128,96,250>/256

If you want to mix colors this way, just use Gimp or another paint 
program and use the eyedropper tool to the get RGB values, and divide 
that color vector by 256.

Sam

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stbenge wrote:
> If you want to mix colors this way, just use Gimp or another paint 
> program and use the eyedropper tool to the get RGB values, and divide 
> that color vector by 256.

Actually, divide by 255 since there are 256 colors, but they are in the 
range 0-255. #FFFFFF; = <255,255,255>/255 = <1,1,1>

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CShake <cshake+pov### [at] gmailcom> wrote:
> stbenge wrote:
> > If you want to mix colors this way, just use Gimp or another paint
> > program and use the eyedropper tool to the get RGB values, and divide
> > that color vector by 256.
>
> Actually, divide by 255 since there are 256 colors, but they are in the
> range 0-255. #FFFFFF; = <255,255,255>/255 = <1,1,1>

Yes! This is a very common mistake that I've seen in lots of code (in various
languages) over the years.


Here are a couple of colour mixing formulas that I find useful. In these
formulas, C, C0 & C1 are colour vectors, and A is a float, 0 <= A <= 1.

//A weighted mean between colours C0 and C1
C0 * A + C1 * (1-A)

//A muted version of colour C
rgb A + C * (1 - A)

In POV-Ray, it's possible to use negative colours, eg rgb<-1, 0, 0> is identical
to rgb <0, 1, 1>. It's also possible to use colours with components greater than
1, but such colours will get clipped in strong light, so it's probably a good
idea to avoid using this "feature".

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Thanks, I already used an external tool to get my rgb values (and divided by
255, pfewww), but being able to weigh colors and use them in formula's is new to
me, and having experimented with that, its really giving me extra possibilities,
very glad with that (I think I'll leave the negative and > 1 colors for what
they are, I'm happy using the classic range)

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> Sometimes when I need a real-life color, I will open a photo with 
> IrfanView and click on the color I want, to read the RGB values. I take 
> those values and convert them in POV like so:
>
> rgb <128,96,250>/256

You do realise that photos are usually in sRGB colour space and POV expects 
linear colour values?  By simply pasting the numbers into POV the colours in 
the resulting image are going to be washed out and probably of the incorrect 
hue...

Better to do a simple inverse gamma correction inside POV (the 2.2 here 
roughly approximates the sRGB -> linear conversion):

rgb <pow(128/255,2.2),pow(96/255,2.2),pow(250/255,2.2)>

That way the colours in your POV output image should match much better what 
you picked in the first place.

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"scott" <sco### [at] scottcom> schreef in bericht 
news:4b13a82f$1@news.povray.org...
> You do realise that photos are usually in sRGB colour space and POV 
> expects linear colour values?  By simply pasting the numbers into POV the 
> colours in the resulting image are going to be washed out and probably of 
> the incorrect hue...
>
> Better to do a simple inverse gamma correction inside POV (the 2.2 here 
> roughly approximates the sRGB -> linear conversion):
>
> rgb <pow(128/255,2.2),pow(96/255,2.2),pow(250/255,2.2)>
>
> That way the colours in your POV output image should match much better 
> what you picked in the first place.
>

This may even be true (in my experience) with any color picker external to 
POV-Ray. Bearing that in mind, I wrote a little macro using your line of 
code:

#macro ColorCorrect(ColorIn)
  rgb <pow(ColorIn.red/255, 2.2), pow(ColorIn.green/255, 2.2), 
pow(ColorIn.blue/255, 2.2)>
#end

Which you can use then whenever you pick an external color, e.g.:

#declare ColorIn = <0.0,  128,  128>; //the color picked externally
sphere {
  0.0, 1
  texture {
    pigment {ColorCorrect(ColorIn) }
    finish{
      specular 0.2
      roughness 0.001
    }
  }
}

Thomas

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> This may even be true (in my experience) with any color picker external to 
> POV-Ray.

Yes mine too, actually I first came across this (a long time ago) when 
trying to put a POV generated file into a power point presentation.  The 
colour of the main object in the POV file was meant to exactly match some 
corporate colour already used in the PPT (as RGB of course).

> Bearing that in mind, I wrote a little macro using your line of code:
>
> #macro ColorCorrect(ColorIn)
>  rgb <pow(ColorIn.red/255, 2.2), pow(ColorIn.green/255, 2.2), 
> pow(ColorIn.blue/255, 2.2)>
> #end

That's a neat idea.  I think there was a discussion a while back about 
having another SDL keyword to specify that literal colours and image maps 
are to be interpreted as sRGB rather than linear values.

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