I performed a manual run of the paint color mixing strategy this weekend to better understand the challenges. The paint color mixing strategy involves mixing together paints in known ratios, allowing the paint to dry, then capturing an average RGB value of the final color. With enough RGB values and associated paint mix ratios, I am hoping it will be possible to algorithmically match an digital image RGB color with a captured RGB paint color.

The first thing I did was modify the paint g-code generation script so the paint management system would dispense a decreasing volume of green paint and increasing volume of white paint (from left to right) in 10% increments. The results are in the image below. The first dispense (far left) is not used; it is done to ensure that paint is flowing out of the syringe nozzles. Total volume of paint in each column is 0.05 cm^3. 

After automatically dispensing the paints, I manually mixed them together and painted them on a white piece of paper. Then allowed the paint to dry. 

I took a photo of the painted paper under repeatable light conditions (i.e. a photography light ring) with my digital camera. 

I used a photo editing program to extract an average RGB value for each painted color. Paint mix ratios and RGB values are shown in the image below.

Finally, I plotted the RGB values in 3D space. 

Main takeaways from this exercise:

• the digital camera measures smaller changes in color than I can perceive
• paint colors can be far from their pure RGB representation (i.e. white paint under these light conditions is not (255,255,255))
• linear paint mixtures in 10% increments may not result in human perceptible differences. I am guessing I could have achieved a perceptible color change at lower green to white ratios than 1:9. 
• linear paint mixtures do not result in linear changes in RGB values
• to be able to algorithmically match digitial image colors to paint colors effectively would require a much larger dataset

My next step is to use this same process to mix green paint with red, blue, and yellow paints. I want to understand the size of color gamut I can achieve using mixtures of two paint colors.