1. What is Color?
Color is related to the wavelength of light. If a color corresponds to one particular wavelength, this is called spectral color.
=600 nm corresponds to a color, but naming it is not an exact science….
orange chrome, golden poppy, spectrum orange, bitter sweet orange, oriental read, Saturn red, cadmium red orange, red orange…

2. A particular color sometimes corresponds to a range of wavelength
Blue: ~ 485 nm
Green: 500 ~ 550 nm
Yellow: 570 ~ 590 nm
Red: ~ 625 nm
Most of the time, however, we see non-spectral colors. We can see a color even when the wavelength of the corresponding spectral color is absent.
There is more to color than meets the eye!

3. Intensity Distribution
Most of the colors we see are not spectral colors, but instead have a distribution of intensity in wavelength (composite color).
For example, a color green may contain all other colors but with the intensity peaked at the wavelength 500 nm.
Our eyes cannot distinguish the colors that are composite from spectral colors. (different distributions may correspond to the same color!)

4. White light reflected from
A greenish region.

5. Classification of colors
Hue: main color. The dominant wavelength in an intensity distribution curve.
Saturation: purity of the color.
Measures how much dominant wavelength there is compared to the amount of white mixed in.
Saturated: all intensity fairly close to the dominant wavelength (spectral color is 100%)
White: complete unsaturated

6. Saturation
White: unsaturated
saturated red
Less saturated red

7. Lightness of surfaces
Lightness has to do with the percentage of incident light reflected at each wavelength. (white: a lot of reflection; black: no reflection)

8. Color tree:
The same position has the same color independent of the spectral intensity!
Trunk completely unsaturated. Out from the trunk, the degree of saturation increases.
The vertical axis is related to lightness (white at the top and black at the bottom.
The hue varies around the tree (green,blue…).

10. Simple color additive rules
Mixing the broad distributions of green and red yields yellow. Although the resulting spectral distribution is very different from spectral yellow (see 9.6g)
If one mixes roughly equal amounts of monochromatic green and red, the result also looks yellow, although the spectral yellow is completely absent. (see 9.6h)

11. Two colors which look alike even though they have different intensity distribution curves, are call metamers.
Mixing blue and green yield cyan.
Mixing red and blue yields magenta.
Add all color together yields a flat intensity distribution which is white. (see 9.6i)

13. Complementary Colors We know that B+G+R = W We know also G+R = Y
Therefore: Y+B = W. And we call Y and B complementary colors.
C is complementary to R
M is complementary to G.

15. Some spectral colors have complementary spectral colors
Some spectral colors have complementary spectral colors. For instance, the complementary of the orange (600nm) is bluish cyan.
Not all spectral colors have complementary spectral colors. For instance, the complementary of green has to be a double humped distribution.

16. Chromaticity Diagram
Question: if given spectral blue, green and red, can any color (hue, saturation, brightness) be matched by mixing them?
Almost!
You cann’t match spectral cyan.
If you choose as your three colors: red (650nm), green (530nm), and blue (460nm) the relative amount of mix to get the spectral color is shown in Fig. 9.10

18. Another way is to see this is the horse-shoe type of diagram, with three colors at three different positions.
The straight-line between the two colors represents all the colors that one can get from the mixture of the two.
All the points in the triangle represents all the colors that one can make with three primary colors.
The spectral colors full outside of the triangle (negative mixing).

20. The complementary of any color is found by extending a straight line from that color through white and to the opposite side of the horseshoe.

21. CIE Chromaticity diagram
Invent three imaginary colors: x, y, z. Then using these colors, one can get all colors with positive amount of mixing.
The imaginary x consisting of 150% red, and a negative 50% green.
For any color, the relative amounts add to 1.
However, all possible colors are still within the horse shoe inside of the triangle.

23. Relative amounts of [x],[y],and [z] needed to match
A give spectral color