
Color wheels are wrong? How color vision actually works - akkartik
http://blog.asmartbear.com/color-wheels.html?
======
joeld42
This article tries to sensationalize and obfuscate something that is pretty
simple in reality.

RGB are the primaries in light. By mixing these three colors you can create
any color the human vision system can perceive (yes, because of tristimulus).

When white light hits a material, some of those RGB wavelengths are absorbed
(subtracted). RGB - GB(Cyan) = Red, RGB - RG(Yellow) = Blue, RGB - RB(Magenta)
= Green. Thus, Cyan, Magenta and Yellow act as primaries (colors from which
you can construct any visible color) for materials that absorb, not emit
light.

The forth primary in print media, Black, is simply added because inks are
imperfect and a mix of CMY inks yields a kind of murky black (plus it wastes
ink).

It's a historical simplification to say that "red, yellow and blue" are the
primaries for paint, the red works like a magenta, the blue works like a cyan.
They sell Cyan/Yellow/Magenta primaries for oil/acrylics and if you paint with
these you'll get a brighter, wider palette but you can get there with a
traditional palette by adding whites and other pigments.

The tone of the article is awful. The opening sentence, "Ask any artist..." is
flatly untrue, this stuff is basic for most visual artists (I first learned
about the CMY primaries in a community ed. Painting I class). It's not that
the article is factually wrong, it's just basic stuff presented as if it were
obscure or clever.

None of this makes the color wheel or any other color theory any less valid.
The "four color" wheel he lists at the end is not wrong, it's just silly: you
could pick any points on the wheel and their opposites and have the same
thing.

~~~
podperson
I think you're right in some respects (e.g. most artists have a much more
sophisticated understanding of color than red, yellow, blue -- that's the
version you get taught in elementary school).

But you're missing the point in others: half the article is devoted to
explaining the inadequacies of the RGB model for handling actual real world
color. (This is why photos of sunsets -- digital or film -- never look right.)

A simple example -- color looks weird under "white" LEDs (at least the current
ones) because they're actually RGB LEDs balanced to create the illusion of
"white" light. Some orange things will look all but black under a white LED
while others will look orange. Why? Because orange light can be actually
orange, or a mixture of wavelengths that gets a similar response from your
eye.

And so on and on. The article is a bit annoying (and it would help if it
assumed most readers will know about CMYK and RGB color models already) but
the fundamental lesson -- that color is more complex than you think and you
need to understand the underlying physics and physiology to really understand
color is worth making.

~~~
jacobolus
> _This is why photos of sunsets -- digital or film -- never look right_

The main reason sunsets don’t look right is that sunsets have a huge dynamic
range, beyond the ability of our printed photographs or computer displays to
reproduce (no one has the sun in their living room).

~~~
podperson
No, the main reason is that RGB is an approximation of color not true color.
Light in the real world isn't RGB. Human beings do not see in RGB. Read the
damn article. (There's also a lengthy post above which tries to make the
points over again.)

Do you think CMYK will reproduce sunsets if you shine a bright enough light on
a piece of paper and use black enough ink? Same argument.

~~~
jacobolus
(yeah, I wrote that lengthy post)

I understand the concept of metamerism. You are quite right about objects
changing appearance from one light source to the next, etc. It’s also true
that sunsets often have colors which are more colorful than can be produced by
computer displays or 4-color-process prints. However, I stand by my assertion
that the _main_ reason that sunsets don’t look right on screen or in print has
to do with the lack of dynamic range.

------
diiq
I'm happy to see someone investigating color, and the way we perceive it. So
many color theory books are more mystical than scientific; it's wonderful to
see a physiological model.

I suspect that we continue to teach the RGB, RBY, and CYMK color wheels
because they behave correctly with respect to the behavior of particular
physical media. Yellow-looking paint and blue-looking paint _do_ make green-
looking paint. Red-looking light and green-looking light _do_ make yellow-
looking light.

The (physiologically accurate?) four-primary-color model proposed here does
not correctly predict the world: yellow and blue act as additive color
opposites; red and green act as subtractive color opposites. No one set of
pigments or lights will ever consistently behave the way this 4 color wheel
predicts.

We need multiple systems because colored _objects_ mix by multiple mechanisms.

~~~
sedachv
It's not really a new thing. Rudolf Arnheim's Art and Visual Perception
(published in 1974, widely read in art school from what I understand) had a
whole chapter about exactly the same material as in that blog post. But before
that it had a chapter on the psychology of color, and why the color wheel is
in fact useful.

~~~
diiq
Right! I used "proposed" to mean "argued for" rather than "set forth for the
first time".

Arnheim is kind enough to distinguish between "generative complements" and
what he calls "fundamental complements", (though I would prefer they be called
"perceptual"). He warns _specifically_ against confusing perceptual color and
color-in-the-world. By making that distinction, Arnheim validates BOTH
systems, rather than attempting to invalidate three-primary systems (as this
article appears to do).

The article calls RGB and RBY color "wrong" and unable to "stand up to even
minor scrutiny".

Arnheim calls them "generative".

I claim their generative nature (that they inform how to _create_ color) is
why they are taught in schools. I'm not denying the four-color idea; I'm just
saying it is based on a different definition of color, and different intended
use of color.

------
lukev
I wish I could upvote this twice. I hadn't realized that our actual perception
of color was so filtered from the physical spectrum.

I find it incredibly fascinating, from a philosophical perspective, that there
are literally color combinations (i.e, greenish-red) that, despite lying
within the physical spectrum to which our eyes are sensitive, _we cannot see_
, cannot even imagine.

~~~
NonMint
The thing that will really blow your mind is are there things that are red, or
a group of things that have a common appearance that our minds just label
"red." And what if what if the signals that reach my brain when I view "red"
are shifted one to the left on the color wheel? The gradual perception of
color change would be perceived but we would be looking at different colors
even though we both agree that it is "Red."

~~~
apl

      > The thing that will really blow your mind is [...]
    

Only if "you" refers to a stoned college kid. The realization that qualia --
such as the redness of red -- are fundamentally subjective is, quite frankly,
an old hat.

------
armandososa

         Artists get it wrong
    

I kinda get upset about all his use of "artist" as a derogatory term. Have he
ever painted anything in real life? Beleive it or not, just a canvas plus red,
blue and yellow acrylic paint will be enough.

Oh, and some kind of talent.

~~~
KevinMS
_Beleive it or not, just a canvas plus red, blue and yellow acrylic paint will
be enough._

This is actually not completely true, but I appreciate the point you are
making.

Something we shouldn't overlook is that there no pigments that fit perfectly
on a color wheel. In other words, there's no blue pigment, its always blueish
green or blueish purple.

This has been a challenge for pigment makers for centuries and has a
complicated history.

Maybe sometimes a perfect pigment or dye is found, color wise, but then it
turns out to easily fade, aka 'fugitive', so artists, the ones who expect
their art work to last for more than a few years, are stuck with certain
colors.

Why does this matter? Its because of mixing. You might think you have paints
of the primaries, blue, yellow, and red, and you need a bright green, so you
mix the blue with the yellow, and you end up with an muddy olive color.

Turns out your blue was leaning towards being purplish, and when mixed with
the yellow, a component of grey was produced, because they are opposite.

So how do you get a nice bright green? You need to mix a greenish blue with a
greenish yellow.

In practice this results in artists, who want to paint with a full range of
colors, need 6 primary colors.

For example, two good lightfast (not destroyed by light) blues are ultramarine
(very old pigment), and a newer phthalo blue (much more modern). The
ultramarine leans towards the violet and the phthalo, to varying degrees,
towards green. In the old days I think prussian blue was the greenish blue of
choice, but its a weak color and is easily overpowered.

Cobalt blue, if I'm not mistaken, is the closest thing we have to a lightfast
primary color.

Artist really hit the jackpot with blues. Some are very old. They are also
nicely transparent, which can make a difference in technique

The bright reds and bright yellows aren't so good, and the ones that are
lightfast are supposed to be toxic. And not very transparent either.

If you don't care about the brightness of your reds and yellows you are in
luck, there are plenty of rust and dirt pigments like iron oxide, sienna and
umber.

This is a complicated subject. Here's a book about it

[http://www.amazon.com/Blue-Yellow-Dont-Make-
Green/dp/0967962...](http://www.amazon.com/Blue-Yellow-Dont-Make-
Green/dp/0967962870)

------
knutae
I find the CIE Standard Observer graph enlightening:
[http://en.wikipedia.org/wiki/CIE_1931_color_space#Color_matc...](http://en.wikipedia.org/wiki/CIE_1931_color_space#Color_matching_functions)

As far as I understand this, the red function, which corresponds to the red
receptors in a typical human eye, reacts mostly to high wavelengths, but also
has a small spike in the lower end of the spectrum. This explains why the
violet end of the spectrum looks similar to red to human eyes, and this is
probably why color wheels seem so natural. After all, a color wheel is almost
the same as rainbow that wraps around.

I also find it fascinating that the CIE color space was defined as early as
1931.

~~~
jacobolus
No, the CIE standard observer is not the same as the responsivities of cone
cells in the eye. That article you linked describes how it was arrived at:

1\. Match monochromatic (narrow wavelength band) light sources of each
wavelength with three particular monochromatic lights (called “R”, “G”, “B”),
in some cases needing to add some of one of those three to the monochromatic
source in order to get the two sides to match – this is a “negative”
component. This process results in three (r(λ), g(λ), b(λ)) functions of
wavelength.

2\. Take three linear combinations of those three functions and call them
(x(λ), y(λ), z(λ)), such that (a) the y(λ) function is approximately the same
as the photopic luminance function as best it could be computed at the time,
(b) all three of x, y, and z had only positive values, and (c) integrating
each of the three yields the same value, so that an equal-energy stimulus will
have the same X, Y, and Z values.

The red receptors in the human eye do not really have this kind of spike in
response in the lower end of the spectrum.

* * *

However, “red” the “psychological primary” or “unique hue” does have some
violet/blue in it. Any monochromatic red light source is a bit on the orange
side.

------
martian
In the early 20th century Albert Munsell did a series of empirical studies to
determine exactly how people see colors relative to one another. The results
are expected, but fascinating.

<http://en.wikipedia.org/wiki/Munsell_color_system>

~~~
jacobolus
Why are the results expected?

(Also, I really need to expand the Munsell Wikipedia article, but Albert
Munsell was dead before much of the empirical work that went into the 1929
Munsell Book of Color – by that point his son was running the company – or
into the 1943 Munsell Renotations, which were based on the work of the Optical
Society of America.)

------
nollidge
I'm getting a 503 error. Obligatory Google cache:

[http://webcache.googleusercontent.com/search?q=cache:oS8AaG3...](http://webcache.googleusercontent.com/search?q=cache:oS8AaG3vxYQJ:blog.asmartbear.com/color-
wheels.html+http://blog.asmartbear.com/color-
wheels.html&cd=1&hl=en&ct=clnk&gl=us&source=www.google.com)

------
steadicat
Why does he conclude that we need 4 primary colors? He knows that our eyes
have three kinds of 'sensors', which roughly correspond to [R, G, B]. How the
brain processes the initial perceptions, allegedly [R-G, (R+G)-B, R+G+B],
doesn't change the fact that you can approximate all colors by mixing
quantities of R, G and B.

What I'd find more interesting is a proposal (or a mention) of a color space
that's based on what are, according to him, the 'computed' values. Something
like NTL (tiNt/Temperature/Luminance), where N is R-G, T is (R+G)-B, and L is
R+G+B. (The names 'tint' and 'temperature' are taken from photo editing
software, as they are the only tools I can think of that come close to this
system.)

~~~
cwp
Actually, this kind of encoding is quite common. Analog television, digital
video and JPEG images are all encoded using brightness, red-green and blue-
yellow channels. The details vary (eg. between YUV, YCbCr and YPbPr) but they
all take advantage of the fact that our eyes are more sensitive to variations
in brightness than to variations in colour. As a result, we can subject the
colour data to higher levels of compression without noticing any visual
degradation of the image.

------
blahblahblah
_So there’s no such thing as "red with a little green" -- there’s just a less
intense red. The brain physically cannot see "greenish-red" because the filter
removes that information._

Under ordinary circumstances this is true. However, it has been shown that the
human brain can be made to see reddish-green, yellowish-blue, etc. Scientific
American published an article about this strange hack of human visual
perception just last year.
[http://www.scientificamerican.com/article.cfm?id=seeing-
forb...](http://www.scientificamerican.com/article.cfm?id=seeing-forbidden-
colors)

------
mambodog
A while ago I submitted an article[1] about the YUV colour system, which takes
into account human perception of brightness/luminance, and how it differs
between colours. It's also an interesting colour system to work with, as the
'Y' channel just stores luminance, so discarding the other two channels gives
you a greyscale image.

I recommend reading it if you haven't already.

[1] <http://nreynolds.co.uk/blog/hsv-is-dead/>

------
jessriedel
EDIT: joeld42 answered my question elsewhere on this page:

<http://news.ycombinator.com/item?id=2166782>

The artists reds and blues are just approximations to the magenta and cyan of
printers.

\----

So I understand that in order to mimic the electromagnetic stimulation to the
cones you only need to control the amount of RGB light hitting the retina. And
I understand that propagating light is additive, so that for light producing
displays you mix amounts of RGB, whereas pigments subtract light, so that for
printing you mix amounts of CMY. (C paint absorbs non-R light, M paint absorbs
non-G light, and Y paint absorbs non-B light.)

I further (kind of) understand that once printing and CRT screens are
explained, there are additional properties of light due to the filters
described in the article.

But can someone explain why the artist's paints are different from the CMY ink
pigments? It seems like it's either (a) something weird about the way paints
mix, (b) artists use paints which somehow take advantage of the filters in the
eye, or (c) a combination.

~~~
lutorm
Maybe you mistyped, but cyan paint _absorbs_ red light, it _reflects_
everything but red, i.e. cyan.

~~~
jessriedel
yes I did

------
sambeau
The checkerboard illusion at the end amazes me every time I see it.

------
kylec
I must have missed something as a seven-year-old, because this is the first
I've heard that blue and yellow were supposed to be opposites. To me, it
always made sense that blue and orange were opposites, both conceptually and
visually. The same with purple and yellow.

~~~
Zaak
It's possible you're an anomalous trichromat:
[http://en.wikipedia.org/wiki/Color_blindness#Anomalous_trich...](http://en.wikipedia.org/wiki/Color_blindness#Anomalous_trichromacy)

------
apl

      > But I digress, and besides I did promise to be all gross
      > and irresponsible, so I’ll stick with that.
      > So there are R, G, and B cones.
    

Cute and all, but so very wrong. There are acceptable simplifications; this is
not one of them.

------
mattmillr
It's interesting that Red/Green and Blue/Yellow colorblindness correlate to
the opposite color pairs that Jason points out. Does anyone know why this is?
Are these types of colorblindness related to a deficiency in the filters (#s 1
and 2) he describes?

------
bobds
Site was temporarily unavailable when I tried to post a comment, so here it
goes:

This post clears up a few misconceptions for me, thanks for that.

I think you will enjoy the following link about "context" related illusions:
<http://www.psy.ritsumei.ac.jp/~akitaoka/color12e.html>

Akiyoshi Kitaoka is a university professor from Japan that has created a very
extensive and amazing collection of illusions, documenting so many subtle ways
our eyes play tricks on us.

His homepage is really worth exploring:

<http://www.psy.ritsumei.ac.jp/~akitaoka/index-e.html>

------
m-photonic
>And magenta? It comes from full R and B with no G, activating Filter #1 full-
positive, Filter #2 at zero.

This doesn't seem right to me. If the second filter were at zero, you should
have a pure red and not something with blue content in it like magenta clearly
has.

I think he may be representing the second filter as R+G-B, when R+G-2B would
make more sense. The latter system shows FFFFFF as being neutral on the
yellow-blue axis, while the former erroneously puts it in the yellow region.

~~~
jacobolus
None of these are straight-forward “linear” sums: there are differing amounts
of each type of cone cell in the retina (and the proportions vary from one
part of the retina to another), there are several levels of combination of
signals which we don’t fully understand currently, the eye/brain adapts to
what it’s just been looking at, what else is in the visual field, what it
knows the light source to be, what “memory colors” it expects for an object,
and so forth.

Thinking of the mechanisms of the eye operating directly on “FFFFFF” is a
_very_ imprecise model for what’s happening.

------
wccrawford
The budding designer in me loves these articles. While I can intellectually
understand the color wheel(s), I'm still having issues grasping it emotionally
and creatively.

------
thret
If you enjoyed that article, you may also like
[http://www.designersreviewofbooks.com/2010/10/interaction-
of...](http://www.designersreviewofbooks.com/2010/10/interaction-of-color-by-
josef-albers/)

It is a beautiful book.

------
sfphotoarts
while the article looks like a mashup of text-books and wikipedia (not to
mention the self-aggrandization) and is interesting, this looks like SEO spam,
one of these sites that sells you some book on how to get rich quick or how to
start your startup.

I think I'll stick with my Johannes Itten.

~~~
michael_dorfman
You talk about what the article "looks like", but have you actually read it?

I found it to be a well-written, well-researched introduction to some of the
problems in color theory. If that's what you mean by "a mashup", then I guess
all secondary literature is.

As for the site, asmartbear is no stranger to these parts, and Jason's posts
are well-regarded.

~~~
sfphotoarts
possibly my British grammar is stumping you, but yes, to read something you
have to look at it.

This article might appear well researched here, but this is the hello-world
equivalent on an art forum.

Maybe if Jason believes he has something meaningful to contribute to color
theory, he should consider updating the Wikipedia page rather than promoting
his own self interest by advertising his book & blog on HN.

~~~
barrkel
> to read something you have to look at it.

It seems basic logic is stumping you: when A implies B, and B is true, it
_does not follow_ that A is true. You assert that you've looked at the
article, and certainly one needs to look at the article to read it, but that
doesn't imply that you've read it.

> this is the hello-world equivalent on an art forum

I fear you might be at the wrong place - Hacker News isn't an art forum.

