Mixing paint colors is complicated as color representation in computers is not optimized for blending. The document discusses using physics-based models like Kubelka-Munk theory to simulate realistic color mixing, but these are difficult to implement. It also explores simply blending colors manually or using other color spaces. Case studies on apps like Krita and Paper show challenges in achieving realistic yet efficient color mixing for digital painting.

1. Mixing Paint!
With Computers!

2. Let’s talk about colors

3. Let’s talk about colors

4. Let’s talk about colors

5. Colors in Code
Colors as combination of Red, green, blue lights

6. RGB Model

7. Mixing Colors

8. Mixing Colors

9. Mixing Colors

10. Mixing Colors

11. Mixing Colors

12. Mixing Colors

13. Mixing Colors
R: 1.0
G: 0
B: 0
R: 1.0
G: 1.0
B: 0
R: 1.0
G: 0.5
B: 0

14. Mixing Colors?
R: 0
G: 0
B: 1.0
R: 0.5
G: 0.5
B: 0.5
R: 1.0
G: 1.0
B: 0

15. So how does mixing paint work?
• Let’s talk about physics

16. Visible Light Spectrum
380 nm 750 nm

21. Subtractive color

22. CMYK color model

24. Mixing Colors Again
C: 1.0
M: 1.0
Y: 0
C: 0
M: 0
Y: 1.0
C: 1.0
M: 1.0
Y: 1.0

25. Now what?
• Other color spaces?
• Need to convert to RGB to display on screen

26. Let’s try physics

27. Kubelka-Munk theory
• Returns reflectance of light for a layer of pigment on a surface

28. Kubelka-Munk theory

29. White
light
Kubelka-Munk theory

30. White
light
Scattering,
Absorption,
Etc.
Kubelka-Munk theory

31. White
light
Scattering,
Absorption,
Etc. Colored light
Kubelka-Munk theory

32. Case Study: Krita Color Blending

33. Case Study: Krita Color Blending
Removed in 2012 :<

34. Kubelka-Munk theory
• It’s complicated to implement.
• Needs information not provided by RGB
• Physically accurate (to a point)
• Can we do better?

38. Case Study: Paper (iPad App)

40. Summary
• Mixing colors is complicated
• Color representation in computers not optimized for blending
colors
• You can use physics!
• Or do it all manually
• To get realistic (or not realistic) color blending

41. Thank you!
Diana Liao
@dmliao

42. Extras
• Stuff that didn’t make it into the 10 minutes, and other links

43. CMYK?
• So the CMY part stands for Cyan, Magenta, and Yellow
• K = Key (Black)
• Avoids using up all your colored inks when printing B&W

44. Color is not intuitive

45. Kubelka-Munk theory
(1–R)²/2R = k/s = Ac/s
Where:
R = reflectance
k = absorption coefficient
s = scattering coefficient
c = concentration of the absorbing species
A = absorbance
Solve for R and convert reflectance to RGB

46. References
• http://vis.computer.org/vis2004/DVD/infovis/papers/gossett.pdf -
a paper for using different color spaces to mix colors, which I
didn’t have time to go over
• https://www.youtube.com/watch?v=lyLPZDVdQiQ – video for
Krita’s paint mixer
• http://www.fastcompany.com/3002676/open-company/magical-
tech-behind-paper-ipads-color-mixing-perfection - article on
Paper’s color mixer

47. References cont’d
• http://www.ftir.ru/docs/%D0%A1%D0%BF%D1%80%D0%B0%
D0%B2%D0%BE%D1%87%D0%BD%D1%8B%D0%B5%20%
D0%BC%D0%B0%D1%82%D0%B5%D1%80%D0%B8%D0%
B0%D0%BB%D1%8B/drift%20theory.pdf – a PDF that comes
pretty close to explaining what it is (and its most often used
form in programs)
• http://www.rpdms.com/wineyrpt.html
• https://quickgit.kde.org/?p=krita.git&a=tree&h=7a7bac0a9ff5767
e59ef856fb3fa9b96865b8eb8&hb=202e453cbae6417748bca3d
93588e0ad4ae1e7c5&f=krita%2Fplugins%2Fextensions%2Fpai
nterlyframework – Krita’s Kubelka-Munk based color mixer, from
a commit back when it was still part of the project
Aka me trying to google the Kubelka-Munk theory