ofColor subtraction

beginners
#1

The ofColor subtraction operator doesn’t work as I would expect: negative results aren’t clamped to 0, but to some positive value:

  
  
  ofColor a(10, 40, 80);  
  ofColor b(20, 5, 30);  
  ofColor c = (a-b); // I get: (246, 45, 50), I would expect: (0, 45, 50)

Im a beginner, so maybe i’m missing something? Is it feature or bug? :slight_smile:
And maybe there’s some other way to find a difference between two colors?

Thanks!
Pawe?

#2

your red channel goes from 0 to 255; 10-20 = -10, but, since your lower limit is 0, your red channel resets to 255 :slight_smile:

#3

I would consider this a bug. When subtracting some value from a color, the last thing you’d expect is the value to be higher afterwards.

#4

imho it depends on the scenario: sometimes something that behaves like a circular buffer could be handy

#5

True, but I think that should really be the exception, not the rule. It’s not a complicated thing to implement so if you ask me we should let it be the task of the programmer.

#6

Hue in HSV colour model is an example of a circular behaviour.

According to the documentation (http://www.openframeworks.cc/documentation/types/ofColor-.html#operator+) operator- should clamp, so this may be a genuine bug. please open an issue at https://github.com/openframeworks/openFrameworks/issues

#7

Afaik ofColor only clamps on rgb, not hsv, which might cause some math problems. Definitely should be be an issue filed for that.

#8

Thanks for all the replies, I’m opening an issue on github then.