Mix RGB colors (L*a*b*)

Question

Hello!

Basically I want two mix two colours color1 and color2. Since simple calculation's bring up stuff like blue+yellow = grey ((color1.r + color2.r)/2 etc) i did some research and found that apparently mixing colors in order for the mixed color to look like we expect it too (e.g. blue+yellow = green) isn't that straight forward.

What another stackoverflow post taught me was that in order two achieve the mixture correctly i'd have to use the L*a*b* space / CIELAB and linked to the wikipedia page about this topic.

I found it informative but i couldn't really understand how to convert RGB to (sRGB and than to) L*a*b* - how to mix the obtained colors and how to convert back

I hope somebody here can help me

Thanks,

Samuel

Answer 1

1) convert sRGB to RGB. From GEGL:

  

static inline double
linear_to_gamma_2_2 (double value)
{
  if (value > 0.0030402477F)
    return 1.055F * pow (value, (1.0F/2.4F)) - 0.055F;
  return 12.92F * value;
}


static inline double
gamma_2_2_to_linear (double value)
{
  if (value > 0.03928F)
    return pow ((value + 0.055F) / 1.055F, 2.4F);
  return value / 12.92F;
}

2) RGB to CIELAB. Look in OpenCV source [/src/cv/cvcolor.cpp]. There are functions for color space conversions [icvBGRx2Lab_32f_CnC3R]

3) mix color channels.

4) make all the color conversions back.