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Newton’s Theory of Color SIR ISAAC NEWTON (1642-1726) discovered that when pure white light passes through a prism, a multi-faceted array of colors resembling a rainbow becomes visible. Based on his findings he created the first color wheel differentiating and defining color in what is called the visible spectrum. The color wheel consists of primary colors known as red, yellow and blue and when mixed create the secondary colors of orange, purple and green. Color then advances by the mixing of the primary and secondary colors to form tertiary colors. Newton published “Opticks” in 1704 which detailed his findings. Young-Helmholtz Trichromatic Theory of Color Vision In the mid 1800’s Herman von Helmholtz (1821-1894), based on the initial findings of Thomas Young (1773-1829), developed the Young-Helmholtz Theory of Color Vision. Young had originally speculated that 3 sets of nerve fibers were necessary in order for the eye to perceive color. Based on later experimentation Helmholtz discovered that in order for us to experience normal color vision, three wavelengths of light are required. Every color in the color spectrum is composed from the mixing of these red, blue and green wavelengths. He performed color matching experiments and found that every person tested could ultimately match any given color by adjusting these 3 wavelengths. In the retina of the eye there are photosensitive pigments that respond to these various wavelengths of light. They respond to the light and interact to enable us to differentiate colors. It was not until many years later that researchers identified the three receptors, called cones, located in the retina used to receive the short (S), medium (M) and long (L) wavelengths to produce color. This became known as the trichromatic theory of color vision. Later research also revealed the existence of other photoreceptors in the retina known as rods which are more sensitive than the cones, but do not distinguish color. 1 Opponent Processing Theory The Opponent Process Theory of color was developed by Ewald Hering in 1892. Hering realized that there are some color patterns that don’t mix, like hues of greens and reds and hues of yellows and blues. He could not reconcile the reasons for this in the previously established Trichromatic Theory. Hering hypothesized that color perception is governed by two opponent systems: the blueyellow mechanism, as well as the red-green mechanism. In the blue-yellow mechanism, blue and yellow are opponents and in the red-green mechanism, red and green are opponents. These colors are called “opponents” because they are controlled by opponent neurons: excitatory and inhibitory neurons. These neurons react to the different wavelengths of colors. In the red-green mechanism, excitatory neurons react to the wavelengths of the color red, while inhibitive neurons react to the wavelength of the color green. Activity in one pair of the mechanism inhibits activity in the other. This is why we perceive after-images when staring at a particular color for a long period of time. For example, when looking at a blue dot for 30 seconds or more, if one were to shift their gaze to a blank, white surface, one would see a yellow dot. The reason for this is when one pair of the opponent mechanisms was being used for an extended period of time the opposite neurons that react to yellow were being inhibited. However, when the gaze shifts to a blank surface, the neurons that reacted to the blue wavelength are no longer stimulated. Consequently, the neurons that react to yellow, which were being inhibited by the over-activity of their opponents finally increase activity. Therefore, in one’s mind, one sees the opponent color, yellow. It was the later work of Dr. Leo M. Hurvich (1910-2009) and Dorothea Jameson (1920-1998) which united these two theories. Their research proved that elements of both theories were necessary and worked in conjunction with each other to create our perception of color. Munsell Color System In 1898 Albert Munsell began the creation of a decimal system to describe color which was detailed in his publication of A Color Notation in 1905. He used the terms hue, value and chroma to systematically evaluate the dimensions of color. Munsell defined hue as "the quality by which we 2 distinguish one color from another.” He defined value as "the quality by which we distinguish a light color from a dark one", and chroma as “the quality that distinguishes the difference from a pure hue to a gray shade”. His description of color is still widely used today. This system is defined as a subtractive system using RYB (red, yellow, blue). Another system is an additive system which is used to refine color on televisions and computer monitors and is identified as RGB (red, green, blue). And in printing CMYK (cyan, magenta, yellow and black) are used to create colors. References 1. George Szekeres (1948), "A New Determination of the Young-Helmholtz Primaries, Journal of the Optical Society of America (JOSA), Vol. 38, Issue 4, pp. 350-363 retrieved from http://dx.doi.org/10.1364/JOSA.38.000350 2. University of Rochester (2005, October 26). Color Perception Is Not In The Eye Of The Beholder: It's In The Brain. ScienceDaily. Retrieved from http://www.sciencedaily.com/releases/2005/10/051026082313.htm 3. Goldstein, E. Bruce (2010). Sensation and Perception. Belmont, CA, Cengage Learning 4. Cherry, K. (n.d.). What is the opponent-process theory of color vision?. Retrieved from http://psychology.about.com/od/sensationandperception/f/opponproc.htm 3 5. Kaiser, P. K. (1996). The joys of visual perception: Opponent processing theory of color vision. Retrieved from http://www.yorku.ca/eye/opponent.htm 6. randomactsofscience.squarespace.com 4. http://www.webexhibits.org/colorart/bh.html 5. http://en.wikipedia.org/wiki/Color_vision 6. http://www.colormatters.com/ 4