
Red, Yellow, and Blue - matan_a
http://www.daveeddy.com/2014/07/01/red-yellow-and-blue/
======
randomdrake
Neat article, but I found it surprising that the author didn't go into a bit
more detail about why RGB is used and where it's used. Saying that it's just
how computers or televisions deal with it because of monitors only offers a
bit of information.

While the explanation of additive and reductive color combining was
interesting, I think it's important to note that it's because you're dealing
with waves of light being absorbed or reflected.

I learned more about color theory and light in stage lighting classes than
anywhere else. Teaching your brain how to combine colors correctly to get the
exact shades you're looking for on the stage is hard. You really do have to
forget a lot of what you learned in art classes to be effective. Understanding
how colored light is absorbed, reflected, or otherwise changed on makeup,
furniture, fabrics, and other surfaces added a whole different level of
complexity not found in typical art classes.

Searching Google for "stage lighting color wheel" reveals more wheels similar
to the one that you see at the author's really cool implementation[0].

[0] - [http://bahamas10.github.io/ryb/](http://bahamas10.github.io/ryb/)

~~~
90hourweek
> Neat article, but I found it surprising that the author didn't go into a bit
> more detail about why RGB is used and where it's used. Saying that it's just
> how computers or televisions deal with it because of monitors only offers a
> bit of information.

It's our eyes. Our eyes are (roughly) RGB, therefore a RGB monitor is a best
spectrum match for our eyes, therefore it's how computers and printers deal
with it (CMY/K/ is just the inverse of RGB).

For many animals, even our best high end lifelike wide-spectrum display cuts
out or inaccurately represents portions of the spectrum they can see.

~~~
VMG
> For example, while the L cones have been referred to simply as red
> receptors, microspectrophotometry has shown that their peak sensitivity is
> in the greenish-yellow region of the spectrum. Similarly, the S- and M-cones
> do not directly correspond to blue and green, although they are often
> depicted as such. It is important to note that the RGB color model is merely
> a convenient means for representing color, and is not directly based on the
> types of cones in the human eye.

It's not that easy though

[http://en.wikipedia.org/wiki/Color_vision](http://en.wikipedia.org/wiki/Color_vision)

> The cones are conventionally labeled according to the ordering of the
> wavelengths of the peaks of their spectral sensitivities: short (S), medium
> (M), and long (L) cone types. These three types do not correspond well to
> particular colors as we know them. Rather, the perception of color is
> achieved by a complex process that starts with the differential output of
> these cells in the retina and it will be finalized in the visual cortex and
> associative areas of the brain.

> For example, while the L cones have been referred to simply as red
> receptors, microspectrophotometry has shown that their peak sensitivity is
> in the greenish-yellow region of the spectrum. Similarly, the S- and M-cones
> do not directly correspond to blue and green, although they are often
> depicted as such. It is important to note that the RGB color model is merely
> a convenient means for representing color, and is not directly based on the
> types of cones in the human eye.

Also there are alternative color spaces like YUV:
[http://en.wikipedia.org/wiki/YUV](http://en.wikipedia.org/wiki/YUV)

~~~
fl0wenol
To elaborate on why the RGB color model is convenient for representing
color...

The choices of RGB in trichromatic reproduction systems are such that the
individual contribution of each minimizes the cross-cone activation in the
eye, allowing greater fidelity (widest gamut) in color reproduction with only
three sensors at input and three emissive colors at output. In other words, if
you're going to use analog electronics and passive filters, it helps to make
the selected primary frequencies as functionally orthogonal and isolated as
possible.

Consider the quality of an absorptive filter and/or response profile of a
pixel on CMOS sensor; so long as a it has a strong peak at the primary
frequency, then we're not too concerned about leakage from other frequencies
into it; nor are we too concerned that nearby colors could leak a little into
the other two channels because this will mostly be correlated with overall
luminance, which makes it very hard for the eye to discern upon reproduction
(it looks a little more washed out).

This is why Young and Helmholtz initially identified red, green and blue as
primary colors way back in the early 19th century. They tried to identify
three specific color frequencies that could be used to mimic other pure
frequencies through re-combination in test subjects, based on a theory about
how the eyes worked. While these colors do not correspond to sensory peaks for
each cone cell type, it turns out the retina/visual cortex's post processing
(the "opponent-process" discovered by Ewald Hering) derives hue from the
combined activation ratios, and is thus bypassed by using combinations of RGB
to create hues as opposed to direct spectral activation.

------
seszett
I think don't even understand the point of the author.

For one, I learnt in school that the primary colours where red, green and
blue, and later that the substractive primary colours where cyan, magenta and
yellow. So nothing different from the RGB/CMYK colour wheels everyone uses.

Second, well nobody will ever be able to create all colours from mixing red,
yellow and blue, plain and simple. Unless your red is actually magenta and
your blue is actually cyan.

At this point, you have just created a colour picker that uses cyan, magenta
and yellow with no easy way to change lightness (without the K scale, you will
have to manually change every colour level to match the global lightness you
want).

 _But_ his implementation has a brightness slider and uses "real" red instead
of magenta, and "real" blue instead of cyan, which makes it a BMYK color
wheel, and which prevents it from reproducing all colours. Even just setting
brightness to the minimum gives a dark brown instead of black, because he's
mixing colors from different models.

~~~
mark-r
I imagine it has to do with how long ago you went to school. I remember
learning that red, yellow, and blue were the primary colors, but that was back
when TVs were black-and-white.

For me the RYB model just seems more intuitive. It just feels natural that
green would be a bluish-yellow. It still seems odd that red and green can be
combined at all, much less produce a pure yellow.

~~~
seszett
> _For me the RYB model just seems more intuitive. It just feels natural that
> green would be a bluish-yellow. It still seems odd that red and green can be
> combined at all, much less produce a pure yellow._

But that's just what the CMY(K) model says. The CMY(K) model is the meaningful
one in everyday life. In actual reality, with human eyes observing physical
light filtered by pigments, blue is just cyan with a little magenta in it, and
red is just magenta with a little yellow in it. The truth is, in the real
world, you will never be able to make cyan or magenta if all you have is
yellow, red and blue paint. But you will be able to make red or blue if you
have yellow, magenta and cyan paint.

I think this might just be a case of people insisting to use less precise but
more familiar names for colours, maybe. Maybe in English "cyan" and "magenta"
sound like strange colours while blue and red sound more familiar and
comforting. But insisting on using blue instead of cyan actually restricts
your ability to draw colours.

------
Bob_Sheep
I couldn't take the article seriously after the suggestion that he was
producing colours that are not seen on a natural rainbow and that the rainbow
is wrong. The spectra for sunlight is almost complete in the visible region
apart from a few small gaps where various elements absorb the light. If you
look at a proper spectrum for sunlight you can clearly see the colours he
claims are missing.

~~~
zokier
Purple (distinct from violet) does not appear on natural rainbows.

~~~
Zancarius
This reminds me of the scuffle about pink. I can't find the original article
linked to from HN, but a quick search yields some interesting disputes:

[http://newsfeed.time.com/2012/03/07/does-the-color-pink-
exis...](http://newsfeed.time.com/2012/03/07/does-the-color-pink-exist-
scientists-arent-sure/)

[http://gizmodo.com/if-the-color-pink-doesnt-
scientifically-e...](http://gizmodo.com/if-the-color-pink-doesnt-
scientifically-exist-why-can-1464266788)

[http://blogs.scientificamerican.com/observations/2012/03/05/...](http://blogs.scientificamerican.com/observations/2012/03/05/stop-
this-absurd-war-on-the-color-pink/)

If there's one saving grace, I suppose it's that we're not tetrachromatics,
right? ;)

~~~
mark-r
But some women are...

[http://discovermagazine.com/2012/jul-aug/06-humans-with-
supe...](http://discovermagazine.com/2012/jul-aug/06-humans-with-super-human-
vision)

~~~
Zancarius
Do be aware that it looks like it's an area that needs further study (and
apparently the "fourth" cell may detect light between red and green). On
average, humans are (generally) not tetrachromats. Poking around on a cursory
search suggests that only one subject in that 2012 study expressed attributes
that were definitive evidence of the existence of tetrachromacy in humans.
Apparently there's some ongoing discussion as to whether or not the optic
nerve is capable of funnelling an extra color channel to the brain, so that'll
be of interest to follow.

Importantly, I was thinking along the lines of some insects and spiders that
are capable of seeing into the UV spectrum for sexual signalling or locating
food sources (e.g. flowers). Which reminds me that there's been some evidence
that suggests those who've had cataract surgery may be able to see deeper into
the violet spectrum without a UV-filtering obstacle in place. But that's
likely just the function of the blue-sensitive cells.

------
wil421
I believe Red, Green, and Blue are the colors of light and Cyan, Magenta, and
Yellow are the colors of pigment.

Apparently the common color wheels, Red Yellow and Blue, are based on Newton’s
prism experiments [1].

[1] [http://learn.leighcotnoir.com/artspeak/elements-
color/primar...](http://learn.leighcotnoir.com/artspeak/elements-
color/primary-colors/)

~~~
Zancarius
> I believe Red, Green, and Blue are the colors of light and Cyan, Magenta,
> and Yellow are the colors of pigment.

Yes, because physiologically, that's how we're wired. We have receptors for
red, green, and blue wavelength light. Everything else is just a matter of how
they get excited.

------
jameshart
This is a rather restrictive approach to the problem of 'I want to choose from
a more aesthetically appealing subset of the colors computers can reproduce'
(where 'aesthetically appealing' is valid for some definition rooted primarily
in experience with physical paints, stubborn adherence to school artroom
dogma, and nostalgia). You could achieve the same effect with a color picker
that only includes the colors traditionally produced by Crayola.

~~~
cmiller1
>You could achieve the same effect with a color picker that only includes the
colors traditionally produced by Crayola.

Apple tried this, kind of.

[http://lowendmac.com/thomas/06/art1025/cpicker.gif](http://lowendmac.com/thomas/06/art1025/cpicker.gif)

~~~
tyilo
It's still there in the latest OS X:
[http://i.imgur.com/40DGTXo.png](http://i.imgur.com/40DGTXo.png)

------
prutschman
If you want to go down a reading rabbit hole about color theory for a while,
check out
[http://www.handprint.com/HP/WCL/wcolor.html](http://www.handprint.com/HP/WCL/wcolor.html)

------
fl0wenol
I stopped thinking in terms of the RYB "color wheel" shortly after middle
school art class. RGB and CYMK seem natural to me.

If you're interested in a color wheel for a picker design that has perceptual
evenness, check the Munsell CS
([http://en.wikipedia.org/wiki/Munsell_color_system](http://en.wikipedia.org/wiki/Munsell_color_system))
... in a color picker it might be cool to select via projections of CIELAB as
the refined version of same.

------
hammock
What I always found fascinating which is not addressed here, is how the
visible light spectrum is a straight line with other "colors" at its ends, yet
somehow our brains cut out that segment of the EM spectrum, and manage to bend
it into a circle, so that color "wheels" make sense to us and flow nicely,
when in fact red and violet are quite separate on the EM spectrum. It's our
brains that play a little trick

~~~
lcrs
I've heard two explanations for this. The first is that the longer wavelength
"red"-ish receptors in our eyes are also excited by the frequencies of light
at the other end of the visible spectrum, so shorter wavelengths than blue
start to appear red again. Unfortunately the graph produced to back this up is
usually that of the CIE colour matching functions, which do indeed have an
obvious lump around purple, but are _not_ derived from measurements. That lump
was added to create a three-primary space which didn't require negative
numbers to encode completely pure single-wavelength colours. That's a problem
which otherwise crops up when you use three primaries based directly on
measurements of the eye, because the three pigments in our eyes are not
selective enough that a single wavelength only activates one receptor. Real
measurements of the pigments don't really back up the idea of extra
sensitivity to purple in the long-wavelength cones.

The second explanation (or suggestion, at least) is more psychological. In the
distant past our eyes had only two colour receptors, and our brains measured
the relative difference between the two, so we percieved colour on a one-
dimensional line - e.g. more "warm" long wavelengths or more "cool" short
wavelengths. At some point we evolved a third receptor, and our brains began
processing this extra input as another perceptual axis orthogonal to the
existing one, which could be described as purple/green against the original
red/blue. Exploring this new 2D space results in a continuous rainbow around
the edges.

------
honksillet
The RYB color model is fine for third graders and cosmeticians but if you want
to understand how color works you need to understand RGB. And yes that goes
painters too. Mixing paint is more complicated than just using a color pick on
your monitor because there is a volumetric/dilutional component and the paints
is rarely a pure color (i.e. red paint is 256,0,0). It is galling that their
are still university level art professor who persist in RYB color wheel
malarky. Nothing irritates me more than the phrase, "we are mixing paint, not
color". You are mixing both!

------
clay_to_n
Cool article! I've understood the difference between additive and subtractive
for a while, but hadn't thought about the discrepancy between RYB and CMY.

I also recommend watching this short video on the origin of ROYGBIV, and why
Indigo probably doesn't really deserve it's own letter - but it got one,
because of European music notation:
[http://www.theatlantic.com/video/archive/2014/01/why-
roygbiv...](http://www.theatlantic.com/video/archive/2014/01/why-roygbiv-is-
arbitrary/283432/)

~~~
qnaal
Anyone considering Newton's methods as 'mystical' (implied 'unscientific')
gives modern institutionalized science much too much credit, and proper
exploratory science much too little.

------
logicallee
There is no RGB value for the cavernous void reaching deep into a cliff, into
which a dark crack gives you a glimpse, which gobbles the burning light of the
noonday sun, or your brightest flashlight, and gives back nothing.

RGB is just 3 pixels of different intensities, next to each other and sitting
on your desk.

------
qnaal
> the real color wheel below, in all of its glory, showing colors you will
> never see on a rainbow produced in nature.

Magenta? sure, everyone agrees is a bastard color- but cyan is on the rainbow
in the spot labeled 'blue', and _your_ blue is labeled 'indigo'.

CAN'T PROVE ME WRONG IMMA COLOR EXPERT

------
mxfh
Two semi-popular color picker extensions for Photoshop that already include
RYB modes:

[http://www.coolorus.com/](http://www.coolorus.com/)

[http://anastasiy.com/colorwheel](http://anastasiy.com/colorwheel)

