Re: Convert frequency to RGB

Jim Hurley Tue, 12 Aug 2003 07:00:04 -0700

Message: 10
Date: Mon, 11 Aug 2003 17:20:41 -0600
Subject: Re: Convert frequency to RGB
From: Dar Scott <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Reply-To: [EMAIL PROTECTED]
On Monday, August 11, 2003, at 04:43 PM, Jim Hurley wrote:

I think I have found what I need. I had hoped I could find an
> algebraic formula for the translation from wavelength to rgb values. I
 did a Google search and found the following program; I will see if I
 can translate it into Transcript.
That should translate OK. As with yours, it changes only red, green or blue at a time, and thus will vary in intensity in ways not intended. The blue-purple looks like it goes too purple to me. The function does attempt to put an envelope over the whole thing that is probably related to sun intensity and eye response.

See how it looks.

Dar Scott

Dar,

Not very well. Still a bit jerky--in the literal sense. I may have to work on this for a while. I've seen some very nice graphics, I think it was in a web page construction application which had a rainbow-line as a demarker between sections.

I wonder if an image like this could be imported into RR and deciphered the RGB values from the image by running the wand (from the 1.1.1 color palette) over it and somehow extract this data.

I think I got the Pascal program translated correctly. It looks like this:

on mouseUP
  repeat with wavelength = 779 down to 381
    set the backgroundcolor of grc 1 to convertWavelength(wavelength)
    wait 1 tick
  end repeat
end mouseUP

function convertWavelength w

switch case w>380 and w <= 419 put .3 + .7*(w-380)/(420-380) into tFactor put -tFactor*(w-440)/(440-380),0,tFactor into results break CASE w >419 and w <=440 put -(w-440)/(440-380),0,1 into results break case w > 440 and w <=490 put 0,(w-440)/(490-440),1 into results break case w> 490 and w <=510 put 0,1,-(w-510)/(510-490)into results break case w> 510 and w<=580 put (w-510)/(580-510),1,0 into results break

  case w>580 and w<= 645
    put 1,-(w-645)/(645-580),0 into results
    break

case w >645 and w<=701 put 1,0,0 into results break case w>701 and w< 780 put 0.3 + 0.7*(780 - w)/(780 - 700) into tFactor put tFactor,0,0 into results break end switch

  repeat with i = 1 to 3
    put round(255*(item i of results)) into item i of tResults
  end repeat

return tResults

end convertWavelength
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Re: Convert frequency to RGB

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