What is the most accurate color wheel?

I received a question the other day. This happens to me all the time. Just a thought here... Maybe I would get fewer questions if I pretended to be ignorant rather than all this pretending to be an expert? I will have to talk with an image consultant about that.

Here is the latest example of things that people want to know.

I have a question for you. I understand that there are different color wheels for different subjects. ... I haven't noticed before...there seems to be two "main" color wheels, but which one is the most accurate?

With the wheels that have 12 colors there seems to be two that come up - one with a red-orange and no magenta, or one with a magenta and no red-orange.

Which one is more accurate? Or are they both accurate but for different reasons?

Thoughts?

Ashley

I have a lot to say on this topic -- enough that I will break it up into two blog posts. In this blog post, I will look at various color wheels, with a eye toward the underlying theory. In the subsequent blog post, I will look at the more general question of the utility of color wheels in general.

Red, blue, and yellow primaries

Here is a color wheel that does not have magenta. This beautiful little color wheel with 72 spokes dates back to a book by Michel Eugene Chevreul in 1839. He was a chemist involved in the dyeing of carpet. His work on color perception came out of trying to understand why dyeing did not always turn out as one expected. This color wheel was his first step in understanding color.

https://knowwithoutborders.org/monet-light-creativity/chevreul-color-wheel/

This is kinda pretty, but the left-hand side of this color wheel is a bit dark for my taste. It could be that the colors faded -- after all, this book was made in 1839 afterall. Or it could be that the creation of the color plates suffered from the fact that a good magenta pigment wasn't invented until 1858.

The image below (on the left) is a black and white version of Chevreul's color wheel, with color words for each of the 12 basic colors. Each of these 12 colors are subdivided into 6 steps to make a total of 72 colors in the wheel. At the right, I show my colorized interpretation.

I drew a little triangle inside my rendition to make a point. The colors red, blue, and yellow are all explicitly called out, and are conspicuously 120 degrees apart. The Chevreul color circle is based on the artists' primaries, red, blue, and yellow.

This color wheel satisfies Ashley's first criteria: "one with a red-orange and no magenta". RO is red-orange, and VR (violet-red) appears maybe somewhere around where magenta might be. Perhaps if the color name magenta existed at this time, it may have been incorporated into the color wheel, but I haven't had the opportunity to query M. Chevreul on the topic.

Red, green, blue primaries

My computer monitor doesn't use the artist's primaries. For some silly reason, it uses red, green, and blue. (Note to self: I need to contact those people who design computer monitors and televisions and screens for cell phones and tablets. They need to learn about the artist's primaries, because clearly that would be a much better way for them to encode color.)

I did a little playing in PowerPoint (my graphics design program of choice) and came up with my own  twelve step program... err, twelve step color wheel. I hope that everyone reading this takes a moment to step back and say "ohhhhhhh...." in appreciation of my epic artistic skills.

The Seymourian twelve-step RGB color wheel

For those interested in the details, the red, green, and blue anchor points are (255, 0, 0), (0, 255, 0), and (0, 0, 255). The halfway points between them are yellow (255, 255, 0), cyan (0, 255, 255), and magenta (255, 0, 255). I filled in the points between using HSL coordinates. The hue of HSL goes through steps of 21.3333 from 0 to 235.

This color wheel fits Ashley's second criteria: "one with a magenta and no red-orange". The magenta is at the very bottom, and there is red, and there is orange, but no steps in between.

Cyan, magenta, and yellow primaries

I have a little bonus for those involved in my twelve step program: a color wheel that is specially designed for anyone involved in printing. Here we see that the basic colors are cyan, magenta, and yellow. Please note carefully that the cyan-magenta-yellow color wheel bears no resemblance at all to the red-green-blue color wheel. None whatsoever. Completely different.

The Seymourian twelve-step RGB color wheel

That last line was just a tiny bit of sarcasm. I said that as a way to highlight the fact that these really are the same color wheel. Both are based on RGB color theory, which is a simplification of scientific color theory. This is a fascinating and illuminating topic, and one which is worth a whole blog post to itself.

Oh... I should mention one thing here. Cyan, magenta, and yellow don't do so well at getting all colors. Early printers found it was a good idea to add black. Oh yeah, one more thing... When you print magenta over cyan, you don't really get blue. It's usually more of a purple. And when you print yellow over magenta, it's not a good red. It's a little too orange.

As a result... lately there has been a lot of kerfuffle about expanded gamut printing, where you print with CMYK, but then add in orange, green, and violet inks to extend the range of colors that you can get. Or sometimes you use red instead of orange, or blue instead of violet.

The artists' primaries

Allow me for the moment to revisit the concept of artists' primaries on which the Chevreul color wheel is based. I was taught in kindergarten that:

1) Red, blue, and yellow are the primary colors.
2) You can make all the colors by mixing appropriate amounts of these three primaries.
3) Red plus blue is purple. Red plus yellow is orange. Blue plus yellow is green.

The first is more of a definition than anything that you can test. But the second and third are testable. The second is hard to test, but I tested the third one during lab period in kindergarten. An actual image of the results of my experiments has not survived, but a rough approximation is shown below.

Artists conception of the artists' color wheel

I recall presenting my disappointing results to Mrs. Reidhouse, who was the main lecturer in my kindergarten class. I also vividly recall trying to explain to her that the lack of saturation in the pairwise mixtures was predictable using the Kubelka-Munk equation. But I don't recall her offering a cogent counter argument in support of the artists' primaries theory of color. I do recall being told that it was nap time, though.  

I was trying to articulate to her a basic postulate of paint mixing: Mixing pigments will usually lead to a loss in richness (chroma) of color. In other words, you can't get a rich, vivid green by mixing yellow and blue. You can't get a rich purple by mixing red and blue.

If you find yourself disagreeing with this, then I suggest you visit an art supply store. If Rule 2 were correct, then you would generally see beginner paint sets with five different paints: red, blue, yellow, white, and black paints. Maybe you would see sets with more colors premixed, but if you look at the ingredients, you would only see those five basic pigments. There would be no need for any others.

This set contains 12 of the most popular colors in 2 oz (59 ml) tubes, including Burnt Umber, Burnt Sienna, Raw Sienna, Yellow Oxide, Naphthol Crimson, Cadmium Orange, Phthalo Green, Yellow Medium Azo, Cadmium Red Light, Ultramarine Blue, Titanium White, and Mars Black.

Still not convinced? Then take a trip to the hardware store and ask to see their paint mixing equipment. Count the canisters... do they mix all the colors of paint with five pigments, or are the dispensing devices "Available as either 12, 14, or 16 canister turntables"?

A manual paint tint dispenser with up to 16 canisters

Here's another suggestion for those not yet convinced. I put together a little a do-it-yourself guide to printing with the artists' primaries instead of CMY. Visit my blog post, print out the supplied images, and see what kind of results you would get if HP supplied you with red, blue, and yellow ink cartridges.

In order to get a full range of colors, you need to start with a variety of pure pigments that cover the full range of colors. The theory of the artists' primaries is just plain wrong. 

Red, yellow, green, blue, and purple primaries

Albert Munsell was a smart guy when it came to color. As proof, there was once an upstart wannabe color guru who was so bold as to refer to Munsell as the Father of Color Science. Munsell devised a color wheel that he actually manufactured with paints. (Before I go on, I need to say that his color wheel, was just part of the Munsell color space.)

Munsell started with five primatries. There were an additional five secondaries squished between those five primaries, and each of those ten hues had ten levels in between. Munsell's color wheel thus had a total of 100 different hues.

My rendition of the Munsell color wheel

I want to share a bit about how he created his physical actualization of the color wheel. I share because this is interesting and not well known. Part of this is reverse engineering and presumption on my part. If I have errors in this, I would be happy to recant.

Munsell started with five primaries: red, yellow, green, blue, and purple. With the exception of purple, he had pigments for each of these that he felt truly exemplified the colors. He had to mix two pigments together to get purple, but I mean, how could he avoid purple?

Next he used a creature known as a Maxwell disk to find complements to each of his first five primaries. This spinning disk would have a portion colored with one of his primaries, like red, and another portion colored with a potential shade for the compliment. The complement of red he called "BG" or "peacock blue". He would adjust the pigments mixed for the second pigment until he attained a gray color when the disk was spun.

The ten basic colors in the Munsell color space are listed below. The primaries are in bold type, which coincidentally all have single letter Munsell hue names. Note that Munsell made these with 8 different pigments.

Munsell hue	Color name	Pigment
5R	Red	Venetian red
5YR	Orange	Orange cadmium
5Y	Yellow	Raw sienna
5GY	Grass green	Emerald green and raw sienna
5G	Green	Emerald green
5BG	Peacock blue	Viridian and cobalt
5B	Blue	Cobalt
5PB	Purple-blue	Ultramarine
5P	Purple	Purple madder and cobalt
5RP	Plum	Purple madder

(From Albert Munsell, A Color Notation, 1919. Pigments are from paragraph 104, pps. 66 – 67; common color names are from paragraph 58, page 35. I received an email from Robin Myers which recounted the formulations for the ten basic colors that were used in the 1st, 2nd, 4th, 5th, 6th, and 7th editions. The only change over that time was that in the first two editions, 5BG was made with viridian as the only pigment, and later editions mixed this with cobalt. I appreciate having the help of experts like Robin to make sure that my blog posts are precise!)

Red, yellow, green, and blue primaries

A quick review...

The Chevreul color wheel and its derivatives is based on the dubious assumption that red, blue, and yellow paints can be mixed to make all colors. The RGB color wheel is based on the primaries RGB that work well for computer monitors and televisions and cell phones and tablets, and have always worked well in coordinating my underwear. The CMY color wheel is based on the colors of inks that seem to work well, but you almost always want to at least add black. Then you have the color wheel based on Munsell's color space, which in turn was based on a set of paint pigments that Albert Munsell decided upon back in the early 1900's.

These color wheels are all based on the color capabilities of physical stuff. Which is a bit odd, since "color" is largely a function of the spectral response of the cones in the eye, and the brain's processing of the signals from the cone.  It would seem that a color wheel would best be based on what goes on inside the human head, doncha think?

Ewald Hering proposed the idea of color opponents in 1892. His theory was that we sense an object as being reddish or greenish, but never both. There is a continuum of red to green where every color falls. Similarly, there is a continuum from blue to yellow. All color are perceived as somewhere on this continuum. Finally, there is a third such continuum between white and black. This general idea has been borne out with what we have learned about how the cones in the eye and the neurons leading to the brain work together to create color perception.

This idea was incorporated into the color wheel of the Natural Color System (NCS) shown below. This system was developed by Anders Hard and first described in 1966. The rendition below shows 40 steps. The NCS color system is perhaps not as well known as the Munsell color system, but both companies are in existence today, both selling books of colors.

This idea of color opponents (red vs green, blue vs yellow, and white vs black) can also be seen in the design of CIELAB, shown below.

Image from XRite website

I won't say much about CIELAB in this blog post, partly because I am getting tired of typing and suspect that most everyone is getting tired of reading. But, I think I can get away with not talking about the CIELAB color wheel, since I don't recall ever seeing a color wheel that was explicitly built on CIELAB. I say this not to diminish anything about CIELAB.

So, what's the answer?

Which one is more accurate?

The color wheel based on the artists' primaries is not bad, but it is based on a flawed proposition about the primaries.

The RGB color wheel works well for colors on a computer screen. The CMY color wheel works marginally well for printed colors. The two together are compatible, which makes them a very good conceptual model.

The color wheels based on the Munsell and the NCS color systems both have a great deal of research built into them, and accurate physical renditions of each can be purchased. They are both a bit of money, but they exist. And  I would call either of these accurate.

I will leave this discussion for the time being. But beware, I will have more to say..

Munsell - the Father of Color Science? (part 2)

Albert Munsell has been called the Father of Color Science. In the previous blog post, I looked at whether he earned that accolade through his crusade to put the Science into Color Science Education. I concluded that he would probably have to share this with Milton Bradley -- the board game magnate. I dunno, though. Saying that Munsell and Bradley are both of the Fathers of Color Science might get a bit weird for some.

Before I continue, Munsell is held in esteem by real color scientists, not just color science wannabes who write corny blogs on color in hopes of being invited to the real people parties. One of those cool people parties is the Munsell Centennial Color Symposium, June 10-15, 2018, MassArt, Boston, MA.

So far, I have only gotten as far as being invited to give a webinar for cool people, which is based on this series of posts.  If you are reading this before Feb 21, 2018, then there is still time to sign up. As further.

Today, I try another possible explanation for why Munsell might be due the honor. Albert Munsell developed the Munsell Color System. Unlike previous two-dimensional color systems, the Munsell Color Space is three-dimensional! That made it way cooler. All of the avid readers of my blog even know why color is three-dimensional.

World famous Color Science Model admires the Munsell Color System

But was he the first to bring 3D to color?

Munsell invented the idea of a three-dimensional color space?

Here is a quote from the Introduction of Munsell's book A Color Notation System (1919). (The Introduction was written by H. E. Clifford. Evidently Clifford was his publicist. The world famous Color Science Model shown above is my publicist.)

"The attempt to express color relations by using merely two dimensions, or two definite characteristics, can never lead to a successful system. For this reason alone the system proposed by Mr. Munsell, with its three dimensions of hue, value, and chroma, is a decided step in advance over any previous proposition."

Hue, value, and chroma

That kinda sounds like three dimensional color was Munsell's idea?

Here is another piece of evidence suggesting that Munsell may have been the guy that brought 3D color to a cinema near you. US Patent #824,374 for a Color Chart or Scale was issued to Munsell in 1906. His disclosure states: "It may assist in understanding the order of arrangement of my charts to know that the idea was suggested by the form of a spherical solid subdivided through the equator and in parallel planes thereto, ..."

Doncha just love drawings from old patents?

Fig. 2 above shows a page where the hues of the rainbow are arranged around the perimeter, with them all fading to gray at the center. This is but one page of color. Previous pages would have a brighter version of this, and subsequent pages would be darker. Fig. 1 shows a cut-away version of these pages assembled into a book.

So, he got the patent! Case closed. Munsell deserves to be the Father of Color Science.

Or did he patent the color space?

But... hold on a sec. Another part of the disclosure in the patent refers to "the three well-known constants or qualities of color -- namely, hue, value or luminosity, and purity of chroma..." In the patent biz, we would refer to that hyphenated word well-known as a pretty clear admission of prior art!

Clearly Munsell did not invent the idea of using three coordinates to identify unique colors. This is why I keep telling my dogs that you have to read patents very carefully to understand what is being patented. My cute little puppies are always ready to get out the pitchforks and torches after doing a quick read of a patent.

In Munsell's paper A Pigment Color System and Notation (The Journal of Psychology, 1912), he refers to a number of previous color ordering schemes by "Lambert, Runge, Chevreul, Benson, and others".

A slice of Munsell

So, I did a little investigation. Munsell also mentioned Ogden Rood as an experimenter in color. I dug out a book named Modern Chromatics, by Ogden Rood. I should point out that using the word modern in the title of a book may not be such a good idea if you want the book to be around for a while. This book was published a while ago, like thoroughly before Modern Millie, like in 1879.

The diagrams below are from Rood's book. They look kinda like representations of three-dimensional things to me!

Cross section of Rood's color cylinder and color cone

Not only does Rood's book predate the Munsell patent by about 30 years, but on page 215, he pushed the discovery of three dimensional color back by a full century: "This colour-cone is analogous to the color pyramid described by Lambert in 1772." That was soooo rood of him!

(That was probably the worst pun of my life. I apologize to the anyone whose sense of humor was offended.)

How about these other color systems?

I stumbled on a website called colorsystem.com which chronicles more color systems that you can shake a crayon at. Here is their list of the three-dimensional color systems which predate Munsell. Are you ready?

Johann Heinrich Lambert, 1772

Tobias Mayer, 1775 

Philipp Otto Runge's Farbenkugel (1810)

I just love the name of his color space. In addition to being a world famous Color Scientist Model, my wife makes a pretty decent savory kugel.

Michel Eugene Chevreul, 1839

William Benson, 1868

Benson touts this as both an additive color space and a subtractive one. Orient it one way and you get RGB axes. Orient it another, and you get (what I would call) CMY. He called them yellow, sea-green, and pink. I have used this trick in classes for years. I had no idea that it was invented so long ago.

Wilhelm von Bezold, 1874

Wilhelm Wundt, 1874

So, including Rood's, we have eight different suggestions for a three-dimensional color space, all of which came before Munsell. Oh... wait, I almost forget the earliest one.

Robert Grosseteste, 1230

This gentleman deserves a bit of comment. The colorsystem entry on Grosseteste is a bit sparse, if you ask me. First, Grosseteste has to share a webpage with Leon Battista Alberti and Leonardo da Vinci. I would be honored to share a webpage with da Vinci, but colorsystem didn't mention that Grosseteste's color system was likely the first three-dimensional color system ever conceived.

I do not mean to malign the good folks at colorsystem (although that would be pretty much in line with my reaction to anyone who knows more than I do). I love their website. I think the whole cover-up of Grosseteste's three-dimensional color system was part of a bigger conspiracy to deprive him of his rightful place in the History of Science. In the words of David Knowles (in The Evolution of Medieval Thought, p. 281, "[Grosseteste] is now only a name ... because his chief work was done in fields where he could light a torch and hand it on, but could not himself be a burning flame for ever."

Roger Bacon, who was one of the thinkers that led our way into the renaissance, would become one of the burning flames kindled by Grosseteste. Thus, we see that Robert Grosseteste had two degrees of separation from Kevin Bacon, who was in the movie Apollo 13, which kinda had something to with with science.

Here is a quote from an in-depth study by some people who sound gosh-darn scholarly. The quote is pertinent to the debate over the first three-dimensional color space: "De colore [the paper from Grosseteste] dates from the early thirteenth century and contains a convincing argument for a three-dimensional colour space that does not follow the linear arguments that Grosseteste had inherited from previous philosophers..." 

Back to the Munsell Color Space

It would appear that my original premise was far from being correct. Munsell did not create the first three-dimensional color space.

BUT!!!! The astute picture looker will notice something critical. Rood gave us color spaces that were a cylinder and a cone. Bezold also gave us a cone, and Grosseteste gave us a double cone. Lambert's was a pyramid. Mayer's was a triangular prism. Runge, Chevreul, and Wundt all provided spheres. The Benson color space is a cube.

Please do me the favor of scrolling up to the diagram entitled "A slice of Munsell". Please do me the favor of identifying the shape of that slice. This reminds me of the time when my shrink gave me a Rorschach test. Him: "What does this ink blot look like?" Me: "An ink blot." I failed the test.

Most of the drawings in Munsell's A Color Notation System depict his color space as being a sphere, but there are a few drawings like Fig, 20 (above) that show that his color space is irregular. In his own words, "Fig. 20 is a horizontal chart of all the colors which present middle value (5), and describes by an uneven contour the chroma of every hue at this level."

The last pages of this book are color plates that are slices from his Color Atlas. Note the distinct non-standard-shapedness of this.

Why was Munsell's color space groundbreaking?

We finally come to the unique and revolutionary feature: The Munsell Color Space is not a standard geometric shape. As shown below, the high chroma red hues stick out a lot further than the blue ones. It's hard to see this, but the yellow hues with the highest chroma are near the top, whereas the richest purples are nearer the bottom.

The Munsell color solid

Munsell took the non-intuitive road not taken, and that has made all the difference. That will be taken up in the next exciting installment of this series!