Color Mixing Principles Of



COLOR MIXTURE, LAWS/THEORY OF. = additive color mixture, principles of. = subtractive color mixture, principles of. = color mixing, principles of. The color of objects in the environment are determined by pigments hat are chemicals on the objects' surface that absorb some wavelengths of light and, consequently, prevent those wavelengths of light from being reflected. Also, different pigments permit different wavelengths to be reflected. For example, a pigment that absorbs short and medium wavelengths of light appears to be "red" because only long ("red") wavelengths are reflected; a pigment that permits only short wavelengths to be reflected appears to be "blue;" and a pigment that permits only medium wavelengths to be reflected appears to be "yellow" or "green." When all wavelengths are reflected equally by a pigment, one gets the experience of "white," "gray," or "black," depending on whether the relative amount of light reflected is high ("white"), medium ("gray"), or low ("black"). The term additive color mixing refers to the mixture of colored lights, whereas the term subtractive color mixing refers to the mixture of pigments (such as paints). Subtractive color mixing occurs when pigments create the perception of color by "subtracting" (i.e., absorbing) some of the light waves that would otherwise be reflected to the eye. For instance, if a blue pigment (which absorbs long wavelengths of light) is mixed with a yellow pigment (which absorbs short wavelengths of light), only the medium-length waves will be reflected, and the resultant mixture will be perceived as "green." Amateur painters, working with pigments, experience subtractive color mixing when they mix all of the paints on the palette together, with the result of a muddy "brown" or "black" color. In this case, the painter "subtracts out" all of the wavelengths by mixing all of the pigments together. Additive color mixing, on the other hand, describes the results of mixing colored lights together. For example, shining a blue light together with red and green-yellow lights on the same spot on a white screen reflects the mixed lights back and gives the perception of a "white" light. Two general laws of additive color mixing, known to scientists as early as the 18th century (e.g., Newton, 1704), are called the three-primaries law and the law of complementarity. The three-primaries law states that three different wavelengths of light (the "primaries") may be used to match any color that the eye can see, if they are mixed in the proper proportions. The "primaries" can be any three wavelengths as long as each one is taken from the three types of wavelengths: one from the long-wave ("red") end of the spectrum, one from the medium-wave ("green," "green-yellow") region, and one from the short-wave ("blue," "violet") end of the visible spectrum. The law of complementarity states that pairs "complements") of wavelengths of light can be reflected so that, when they are added together, they give the visual sensation of a "white" light. An important subfield in the area of color vision and color mixture is called colorimetry, which is the science that aims at specifying and reproducing colors as a result of measurement. Colorimeters may be of three types: color filter samples for empirical comparison; monochromatic colorimeters that match colors with a mixture of monochromatic and white lights; and trichromatic colorimeters in which a match is achieved by a mixture of three colors. See also ABNEY'S LAW; COLOR VISION, THEORIES/LAWS OF; GRASS-MAN'S LAWS; NEWTON'S LAW/PRINCIPLES OF COLOR MIXTURE; VISION/SIGHT, THEORIES/LAWS OF. REFERENCES

Newton, I. (1704). Opticks. London: Smith. Grassman, H. (1853). Sur theorie der farbenmischung. Poggendorf Annales der Physik , 89, 69. OSA Committee on Colorimetry. (1943).

The concept of color. Journal of the Optical Society of America, 33, 544.

OSA Committee on Colorimetry. (1944).

The psychophysics of color. Journal of the Optical Society of America, 246, 254-255.

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