Additive and Subtractive Colors Systems

2.  What is the difference between adding and subtracting colors?  What does that even mean? 

                                       Figure: Subtractive Coloring

Subtracting colors are caused by a mixture of colors, from either paints, inks, or almost anything within the natural environment, absorbing certain wavelengths of light while subtracting others. Paints, inks, and other such colored things contain pigments that selectively absorb certain wavelengths while reflecting others; therefore, subtracting certain wavelengths from our vision.  The color that we perceive and see is based on which parts of the electromagnetic spectrum that are reflected.  As an example, red paint absorbs shorter wavelengths while reflecting longer wavelengths producing the perceptual color of red that we see.  When mixing one subtractive color with another it further limits the reflected light thereby producing a darker color.  For instance, mixing the three secondary colors magenta, yellow, and cyan produces the color black.  Furthermore, the subtractive color system originates from white light, which is a blend of all the colors in the visual spectrum.  The different paints and other objects or substances then subtract certain wavelengths from this light producing a certain color that we perceive. 

 

                          Figure: Additive Coloring

While subtractive colors are often seen in nature, additive colors are rarely seen naturally and are often for purposes of entertainment or research.  James Clerk Maxwell is given credit for first showing the concept of additive colors.  He projected the colors of red, green, and blue producing a full color image.  Additive colors, different from subtractive colors, involve light emitted from a light source or some other sort of illuminant thereby forming perceived colors through emission rather than through reflection and also through the process of adding wavelengths rather than subtracting them.  This process usually involves a combination or mixture of the primary colors red, blue, and green to produce other colors often producing secondary colors such as magenta, cyan, and yellow.  Contrary to subtractive colors in which mixing the three secondary colors magenta, cyan, an yellow to produce black, additive colors instead uses a mixture of the three primary colors red, green, and blue to produce white.  Furthermore, additive colors due not coincide with the normal color mixtures that we are used to in our everyday lives such as mixing blue and yellow to produce green.  An example of an additive mixture is combining red and green to produce yellow, although not simple combination can be used to produce green.  Moreover, additive colors are produced from the way our eyes detect different colors instead of being the property of light such as with subtractive colors.  The properties of our nervous system allow us to perceive a wide range of colors through the additive coloring system.  For example, with subtractive colors, our nervous system perceives the color yellow through its reflected wavelength of about 5700-580 nm.  The perception of the additive color yellow is on the other hand a mixture of red and green light.

 

                  

                     Figure: Absorption Spectra of Cone and Rod Cells (http://upload.wikimedia.org/wikipedia/commons/thumb/6/65/Cone-response.svg/410px-Cone-response.svg.png)                    

          Lastly, whether with additive or subtractive colors, our perception of colors is accomplished by matching with our trichromatic color vision.  Our trichromatic color vision is caused by the three types of cones cells in the body, S, M, and L, each corresponding and being sensitive to a certain range of wavelengths.  These three types of cones  respond both to the light and intensity of the light that reaches them through the retina.  Through having to depend on both light and intensity, the brain often needs input from a combination of two types of cones to be able to properly perceive color. 

(Citations:       http://en.wikipedia.org/wiki/Additive_color

                        http://en.wikipedia.org/wiki/Subtractive_color

                        http://en.wikipedia.org/wiki/Trichromatic

Randolph, Blake, and Sekuler Robert. Perception. 5th ed. Boston: McGraw Hill, 2006. 243-244.)