Claim: all colors can be represented by a mixture of 3 primary colors.
Is this true?!
This theory is based on the hypothesis of that the retina has 3 kinds of color sensors called cones.
Color Response Curve for Cones
The above graph the response curves for each of the cones. The peak of the response curves for the 3 cones fall roughly at the wavelengths assoiciated with blue (445nm), green (535nm), and red (575nm, which is actually closer to yellow than red).
RGB Colors:
Since the eye only has three types of receptors responsive to visible light, our perception
of any color spectrum should be able to be represented by the combination of just three signals.
We choose these to be red, green, and blue because they are in the peak response range of
each of the cones. This works rather well but as we shall see below is not perfect.
See Java Applets - RGB values for Spectral Colors
For more information on rods and cones and other vision related information:
Given an arbitrary spectrum of light, how do we calculate the RGB values that match the perceived color of the spectrum as closely as possible?
To answer this question, we start by asking what are the RGB values for very simple spectra, namely the spectra containing a single wavelength. These are referred to as spectral colors.
The RGB values for the spectral colors are measured empirically using the setup shown below.
See Java Applet - RGB values for Spectral Colors
Full list of color spectrum applets. Experimental Set-up: The graph below ( called color matching functions) shows the coefficients, ie.e how much of each of these 3
components is needed to produce a given color. Unfortunately, the only way that we obtain a match for all monochromatic
wavelengths is if we allow the values to go negative - but what does it mean to have a negative light source? Color Matching Functions
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Choose 3 equal energy monochromatic light sources (the primaries) call them red, green, blue. Take a reference
set of monochromatic colors of the spectrum and try to match each light in this set with combinations of the 3
primaries. As shown below, each frequency of light (test source) illuminates the viewing screen on one side of
the partition. The viewer then adjusts how much of each of the RGB colors are needed to produce the same color
as the test source. The amount of each color is what is plotted in the graph above.
The RGB Color Cube
