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Index › Programming Questions & Help › Syntax Questions › Processing calculating hue wrong??
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Processing calculating hue wrong???? (Read 628 times)
Giles
Processing calculating hue wrong????
Feb 27th, 2010, 3:38pm  
I'm confused by this. I picked a colour from the colour selector in Processing  (red: 78 green: 116 blue: 97) - and it indicated the hue was 150.

I then wrote this little program to check a hue-calculating formula I found on Wikipedia.

Code:
color c = color(78, 116, 97); //hue 150

float phue = hue(c);
float chue = 180/PI*atan2( sqrt(3)*(green(c)-blue(c)) , 2*red(c)-green(c)-blue(c) );

println("Processing Hue: " + phue);
println("Calculated Hue: " + chue);


Results:

Processing Hue: 106.25
Calculated Hue: 149.99998

Something weird is going on here. The formula returns the correct hue originally chosen, but Processing's hue function calculates it as 106.25.

I checked with the colour picker in Photoshop to make sure it wasn't the colour selector in Processing that was reporting the hue incorrectly....it wasn't.

Is this a bug in Processing, or have I missed something?
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frankBerg
Re: Processing calculating hue wrong????
Reply #1 - Feb 27th, 2010, 5:14pm  
hello

The default colorMode in processing ranges from 0 to 255,
seems like you are calculating in 360 range
106.25 * 360.0 / 255.0 = 150.0
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Giles
Re: Processing calculating hue wrong????
Reply #2 - Feb 27th, 2010, 6:06pm  
Oh yeah...of course. I feel stupid now.

Code:
color c = color(78, 116, 97); //hue 150

colorMode(HSB, 360, 100, 100);
float phue = hue(c);
colorMode(RGB, 255, 255, 255);
float chue = 180/PI*atan2( sqrt(3)*(green(c)-blue(c)) , 2*red(c)-green(c)-blue(c) );

println("Processing Hue: " + phue);
println("Calculated Hue: " + chue);


Processing Hue: 150.0
Calculated Hue: 149.99998
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