- PAINTS: Sennelier French Artists’ Watercolors: French ultramarine blue, cobalt blue, alizarin crimson, bright red, lemon yellow, yellow ochre, burnt sienna, burnt umber, turquoise green
- FEATURED BRUSHES: Raphaël SoftAqua No. 6, Raphaël kolinsky Series 8404 No. 14
- ADDITIONAL SUPPLIES: Cretacolor Graphite Aquarelle pencils
Is there an algorithm for color mixing that works like mixing real colors?
The common mixing of RGB colors is very different from mixing colors for paintings, it’s mixing of light instead mixing of pigments. For example:
Blue (0,0,255) + Yellow (255,255,0) = Grey (128,128,128) (It should be Blue + Yellow = Green) Is there any known algorithm for color mixing that works like mixing real colors?
My approach
I’ve already tried following: Converting both colors to HSV and mixing hues (multiplied by coefficient computed from saturation), and a simple average for saturation and value channels. Then I computed average luminance from both colors and adjusted the resulting color to match this luminance. This worked quite well, but the hue mixing was sometimes wrong, e. g.:
Red (Hue 0°) + Blue (Hue 240°) = Green (Hue 120°) I’ve figured out that sometimes I need to shift the hue value by 360° (when the difference between hues is greater than 180°).
Red (Hue 360°) + Blue (Hue 240°) = Magenta/fuchsia (Hue 300°) But this shifting wasn’t very good too, e.g.:
Cyan (Hue 179°) + Red (Hue 0°) = Hue 89.5° Cyan (Hue 181°) + Red (Hue 0°) --> shifting is performed (the difference is greater than 180°) Cyan (Hue 181°) + Red (Hue 360°) = Hue 270.5° (Hue 179 + Red) and (Hue 181 + Red) results in two completely different colors. Then I tried CIE Lab color space (as in Photoshop), which is designed to be closer to how humans perceive the colors. I used just a simple average for each corresponding two channels, but the results weren’t satisfying, for example, I got pink (64, 26, -9.5) out of blue (98, -16, 93) and yellow (30, 68, -112). These coefficients were taken from Photoshop. Maybe if I used some different operation than average, it could work, but I don’t know what. CMYK didn’t work too, results are just like in RGB or LAB. It seems that neither the trivial additive nor subtractive color mixing in any of these color spaces yields natural results.
Working implementations
Raster graphics editor Krita had a working implementation of more realistic color mixing at some point: http://commit-digest.org/issues/2007-08-12/ (Painterly mixer plugin) They say it is the first public application that implements special technology using Kubelka and Munk equations that describe the behavior of pigments. Here’s a video of Krita color mixing: https://www.youtube.com/watch?v=lyLPZDVdQiQ
There’s also article about color blending in the Paper app for iOS developed by FiftyThree. They describe how they innovate and experiment in the area and also offer samples of mixing blue and yellow that results in green. However, the actual process or algorithm isn’t really described there. Quoting:
“In searching for a good blending algorithm, we initially tried interpolating across various color-spaces: RGB, HSV, and HSL, then CieLAB and CieLUV. The results were disappointing,” says Chen. “We know red and yellow should yield orange, or that red and blue should make purple—but there isn’t any way to arrive at these colors no matter what color-space you use. There’s an engineering axiom: Do the simplest thing that could possibly work. Well, we had now tried the easiest possible approaches and they didn’t feel even remotely right.”
It seems that same as Krita, Paper implements the Kubelka-Munk model:
[. ] the Kubelka-Munk model had at least six values for each color, including reflection and absorption values for each of the RGB colors. “While the appearance of a color on a screen can be described in three dimensions, the blending of color actually is happening in a six-dimensional space,” explains Georg Petschnigg, FiftyThree’s co-founder and CEO. The Kubelka-Munk paper had allowed the team to translate an aesthetic problem into a mathematical framework. [. ]
From all this information, it seems that implementation based on the Kubelka-Munk model could be the way forward and offer results that are much closer to reality. Even though it looks like a complicated process, I haven’t yet seen much good information on how to implement something like this.
What Colors Make Gray? | Color Mixing with the Primary Colors
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Harness the power, or embrace the subtlety, of this versatile hue by mixing your own versions using primary colors.
Watercolor artist Keiko Tanabe invites us into her studio to learn color mixing alongside her. She shows how subtle neutrals can be — even made with primary colors — and answers a popular question: what colors make gray?
Vibrant colors don’t sing without neutrals. Light doesn’t shine without darkness. Large shapes only seem large when placed next to something smaller. Creating a harmonious relationship of opposites — bright/neutral, light/ dark, positive/negative — in a painting is a balancing act. I try to underscore the dynamics of dichotomy by using the yinyang concept that two opposing components are a whole, with one complementing the other.
Applying this idea to our color choices helps us create more harmony and impact in our work. For example, a bright color pops when neutrals surround it, while a dash of a cool hue stands out among warm hues. Gray can be subtle or make a strong statement. What colors make gray? The color isn’t simple, but we can take advantage of its complexities and evocative quality to create mood and atmosphere in a painting. I’ll explore the power of gray and explain my paint combinations for mixing and using warm and cool grays.
How to Mix Grays
Learning how to work with gray can breathe more life into our art. But, to maintain the transparency of watercolor, we don’t want to add white to black to make gray. And, while they’re lovely colors, using pre-mixed grays such as Payne’s gray or Davy’s gray can look flat if they’re overused in a painting.
So, what to do? In my opinion, gray looks more interesting when it’s mixed from other colors. With this in mind, it’s important to choose paints that mix well. While the number of ways of creating beautiful grays is endless, the easiest may be to mix the three primary colors — red, yellow and blue.
Another option is to use a pair of complementary colors (one primary and one secondary), such as blue and orange, red and green, or yellow and purple. These are just a few of the many combinations that are possible, but they’re a good starting place, especially since most of us have these colors readily available in our palette.
What Colors Make Gray
To mix a basic gray, I use three primary colors, such as alizarin crimson for red, yellow ochre for yellow and French ultramarine for blue. The color temperature can be made warmer by using more alizarin crimson or cooler by using more French ultramarine. Essentially, this method is the same as using two complementary colors (one primary and one secondary) to mix gray: red and green, blue and orange, and yellow and purple.
Demo — Gray Matters
Artist’s Toolkit
- PAINTS: Sennelier French Artists’ Watercolors: French ultramarine blue, cobalt blue, alizarin crimson, bright red, lemon yellow, yellow ochre, burnt sienna, burnt umber, turquoise green
- FEATURED BRUSHES: Raphaël SoftAqua No. 6, Raphaël kolinsky Series 8404 No. 14
- ADDITIONAL SUPPLIES: Cretacolor Graphite Aquarelle pencils
Step 1
After drawing the composition using a 4B pencil, I use diluted yellow to apply an initial wash for the middle of the street. I then surround it with slightly darker values of warmer, muted colors comprised of alizarin crimson, cobalt blue and burnt sienna.
Step 2
As the initial wash dries, I quickly add even darker values of grays — comprised of burnt umber and French ultramarine — on both sides of the street.
Step 3
As the initial wash dries, I quickly add even darker values of grays — comprised of burnt umber and French ultramarine — on both sides of the street.
Step 4
I place cobalt turquoise above the buildings on the left side to cool the color temperature slightly.
Step 5
I mix a neutral gray using cobalt blue, alizarin crimson and yellow ochre to paint some clouds and the distant background.
Step 6
To define important shapes and create contrast, I mix a strong, dark gray using French ultramarine, alizarin crimson and burnt umber.
Step 7
I add small details and another big wash of slightly cooler gray on the lower-right corner to unify and balance the painting.
Final
To add more interest and realism to Kyoto at Dusk (watercolor on paper, 14×20), I add small dots of bright red, cobalt turquoise and lemon yellow to indicate traffic lights and headlights.
Watch Keiko at the Easel
Enjoy this video of Keiko exploring the world around her and at work creating a lovely watercolor! Listen as she talks through her process and creates magical moments on the surface of her painting. Sponsored by Savoir-Faire.
About the Artist
Keiko Tanabe is an award-winning painter, author and workshop instructor. She’s a founding member of the North American Watercolor Artists, a signature member of the National Watercolor Society, and a member of the American Watercolor Society and the American Impressionist Society, Inc.
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I recently completed a workshop with Keiko Tanabe. She completed two painting demonstrations per day. Keiko circulated among the students offering guidance and encouragement. The time passed too quickly. I hope to join another Keiko Tanabe workshop in the not too distant future.
