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{ RCSid $Id: hsv_rgb.cal,v 1.1 2019/07/24 21:36:28 greg Exp $ }
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{
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Convert between HSV (hue, saturation, value) and RGB
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Hue angles are in degrees, from 0 to 360.
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From Wikipedia July 2019
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}
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eq(a,b) : if(a-b+1e-6, b-a+1e-6, -1);
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mod(n,d) : n - floor(n/d)*d;
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Hprime(M,m, R,G,B) : if(m-M+.001, 0,
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if(eq(M,R), mod((G-B)/(M-m),6),
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if(eq(M,G), (B-R)/(M-m) + 2,
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(R-G)/(M-m) + 4)));
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Sprime(M,m) : if(M-1e-4, (M-m)/M, 0);
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H(R,G,B) : 60*Hprime(max(R,G,B),min(R,G,B), R,G,B);
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S(R,G,B) : Sprime(max(R,G,B),min(R,G,B));
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V(R,G,B) : max(R,G,B);
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frevprime(S,V,k) : V - V*S*max(min(k,4-k,1),0);
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frev(H,S,V, n) : frevprime(S,V, mod(n+H/60,6));
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R(H,S,V) : frev(H,S,V,5);
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G(H,S,V) : frev(H,S,V,3);
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B(H,S,V) : frev(H,S,V,1);
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