<p>After researching this a bit more, I believe this is actually a <em>biology</em> question, not a physics one.</p>

<p>The specific term I believe you're searching for is <strong>Trichromacy</strong>, which <a href="http://en.wikipedia.org/wiki/Trichromacy" rel="noreferrer">Wikipedia defines as</a>:</p>

<blockquote>
  <p>Trichromacy or trichromaticism is the condition of possessing three independent channels for conveying color information, derived from the three different cone types.<a href="https://i.sstatic.net/MGK5F.png" rel="noreferrer">1</a> Organisms with trichromacy are called trichromats.</p>
</blockquote>

<p>Reading the Wikipedia article, it appears that the <a href="http://en.wikipedia.org/wiki/Cone_cell" rel="noreferrer">cone cells</a>  Humans (and other trichromats) come in three different variations; the different variations are sensitive to red, green, and blue light, as depicted in this image <a href="http://en.wikipedia.org/wiki/File:Cones_SMJ2_E.svg" rel="noreferrer">(again from Wikipedia)</a><sup>1</sup>:</p>

<blockquote>
  <p><img src="https://i.sstatic.net/MGK5F.png" alt="Normalized responsivity spectra of human cone cells, S, M, and L types"></p>
  
  <p>Normalized responsivity spectra of human cone cells, S, M, and L types</p>
</blockquote>

<p>We've evolved these three cone types because red, green and blue are <a href="http://en.wikipedia.org/wiki/Additive_primaries#Additive_primaries" rel="noreferrer">additive primaries</a>, meaning most of the whole range of visible light can be represented by combinations of these colors. Quoting Wikipedia again:</p>

<blockquote>
  <p>Even the four-primary technology does not yet reach the range of colors the human eye is theoretically capable of perceiving (as defined by the sample-based estimate called the Pointer Gamut[17]), with 4-primary LED prototypes providing typically about 87% and 5-primary prototypes about 95%. Several firms, including Samsung and Mitsubishi, have demonstrated LED displays with five or six "primaries", or color LED point light sources per pixel.[18] A recent academic literature review claims a gamut of 99% can be achieved with 5-primary LED technology.</p>
</blockquote>

<p>I'm not sure what the experiment you're referring to was, but I doubt it would translate nearly as nicely into sound, as RGB is based on the biology of the eye specifically.</p>

<p><sub>1: Attribution: <a href="http://en.wikipedia.org/wiki/User:Vanessaezekowitz" rel="noreferrer">Vanessaezekowitz</a> at en.wikipedia</sub></p>

CC BY-SA 3.0
2013-04-19T21:22:32.920Z
2013-04-19T21:29:12.900Z
2013-04-19T21:29:12.900Z
Josh
<p>I read that there're some more colors which cannot be represented by R,G,B. What is the experiment that lead people to use 3 variables R,G,B? </p>

<p>Can that experiment be replicated in other modals, such as what is the dimension of auditory perception, or tactile perception?</p>

CC BY-SA 3.0
2013-04-19T21:12:50.087Z
This is actually a physics question I believe. All the visible colors of light can be represented by combinations of red, green, and blue. See: http://en.wikipedia.org/wiki/RGB_color_model and http://en.wikipedia.org/wiki/Additive_primaries#Additive_primaries
Josh
CC BY-SA 3.0
2013-04-19T21:26:05.467Z
Nope, I'm wrong! See my answer below.
Josh
CC BY-SA 3.0
2013-04-19T23:33:29.273Z
there are other color representation spaces too,  e.g., L*a*b http://en.wikipedia.org/wiki/Lab_color_space
Memming
CC BY-SA 3.0
2013-04-20T20:25:24.197Z
Thanks! I know that, but why is dimension 3? Why not 2 dimension, or 10 dimension??
Dzung Nguyen
CC BY-SA 3.0
2013-04-21T13:48:00.293Z
Because we have three types of cone cells in our eyes, is my understanding from what I've read.
Josh
<experimental-psychology>
Why do we use 3 channel R,G,B to represent color?
Dzung Nguyen
# Why do we use 3 channel R,G,B to represent color?

(Asked by: username_0 on 2013-04-19)

I read that there're some more colors which cannot be represented by R,G,B. What is the experiment that lead people to use 3 variables R,G,B?

Can that experiment be replicated in other modals, such as what is the dimension of auditory perception, or tactile perception?

**Tags:** experimental-psychology

> **Comments:**
> **username_1**: This is actually a physics question I believe. All the visible colors of light can be represented by combinations of red, green, and blue. See: http://en.wikipedia.org/wiki/RGB_color_model and http://en.wikipedia.org/wiki/Additive_primaries#Additive_primaries  
> **username_1**: Nope, I'm wrong! See my answer below.  
> **username_2**: there are other color representation spaces too,  e.g., L*a*b http://en.wikipedia.org/wiki/Lab_color_space  
> **username_0**: Thanks! I know that, but why is dimension 3? Why not 2 dimension, or 10 dimension??  
> **username_1**: Because we have three types of cone cells in our eyes, is my understanding from what I've read.  

---

## 1 answers

### Answer by username_1 on 2013-04-19. Score: 7 | Accepted answer

After researching this a bit more, I believe this is actually a *biology* question, not a physics one.

The specific term I believe you're searching for is **Trichromacy**, which [Wikipedia defines as](http://en.wikipedia.org/wiki/Trichromacy):

> Trichromacy or trichromaticism is the condition of possessing three independent channels for conveying color information, derived from the three different cone types.[1](https://i.sstatic.net/MGK5F.png) Organisms with trichromacy are called trichromats.

Reading the Wikipedia article, it appears that the [cone cells](http://en.wikipedia.org/wiki/Cone_cell) Humans (and other trichromats) come in three different variations; the different variations are sensitive to red, green, and blue light, as depicted in this image [(again from Wikipedia)](http://en.wikipedia.org/wiki/File:Cones_SMJ2_E.svg)1:

> ![Normalized responsivity spectra of human cone cells, S, M, and L types](https://i.sstatic.net/MGK5F.png)
>
> Normalized responsivity spectra of human cone cells, S, M, and L types

We've evolved these three cone types because red, green and blue are [additive primaries](http://en.wikipedia.org/wiki/Additive_primaries#Additive_primaries), meaning most of the whole range of visible light can be represented by combinations of these colors. Quoting Wikipedia again:

> Even the four-primary technology does not yet reach the range of colors the human eye is theoretically capable of perceiving (as defined by the sample-based estimate called the Pointer Gamut[17]), with 4-primary LED prototypes providing typically about 87% and 5-primary prototypes about 95%. Several firms, including Samsung and Mitsubishi, have demonstrated LED displays with five or six "primaries", or color LED point light sources per pixel.[18] A recent academic literature review claims a gamut of 99% can be achieved with 5-primary LED technology.

I'm not sure what the experiment you're referring to was, but I doubt it would translate nearly as nicely into sound, as RGB is based on the biology of the eye specifically.

1: Attribution: [Vanessaezekowitz](http://en.wikipedia.org/wiki/User:Vanessaezekowitz) at en.wikipedia


---

