CODEWITHSUNDEEP
iphoneobjective-ccocoa-touchcolors
llk
llk

Reputation: 23

Converting RGB values to CMYK

I have RGB values that I need to convert into CMYK values. I'm using the iPhone SDK to try and do this.

I have tried a couple of things, but cannot either get the values to be anything other than 0 or 1, or the K element is completely wrong (showing up as a negative number).

Any help would be a life saver!

Sorry, code:

float k = MIN(1-red,MIN(1-green,1-blue));
float c = (1-red-k)/(1-k);
float m = (1-green-k)/(1-k);
float y = (1-blue-k)/(1-k);

NSLog(@"%d %d %d %d",c,m,y,k);

With the following values for red, green and blue:

93, 37 and 27 I get the following values back:

0 0 1073741824 1071858897

Upvotes: 2

Views: 1941

Answers (2)

Mark Ransom
Mark Ransom

Reputation: 308130

Your formula expects values in the range of 0 to 1, but you're feeding it the more common range of 0 to 255.

float k = MIN(255-red,MIN(255-green,255-blue));
float c = 255*(255-red-k)/(255-k); 
float m = 255*(255-green-k)/(255-k); 
float y = 255*(255-blue-k)/(255-k);

You'll also need a special case when k==255, otherwise you'll get a divide by zero.

Upvotes: 4

Carl Norum
Carl Norum

Reputation: 224864

You have a few problems:

  1. You're using 1-red, 1-green, etc. That indicates that your code expects red, green and blue to be values between 0 and 1, not large integers like 93.
  2. %d is the format specifier for an integer, and you're passing float arguments

Upvotes: 1

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