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PHOTOMETRY AND COLORIMETRY Chapter 2 dealt with human vision from a qualitative viewpoint in an attempt to establish models for monochrome and color vision. These models may be made quantitative by specifying measures of human light perception. Luminance measures are the subject of the science of photometry, while color measures are treated by the science of colorimetry. | Digital Image Processing PIKS Inside Third Edition. William K. Pratt Copyright 2001 John Wiley Sons Inc. ISBNs 0-471-37407-5 Hardback 0-471-22132-5 Electronic 3 PHOTOMETRY AND COLORIMETRY Chapter 2 dealt with human vision from a qualitative viewpoint in an attempt to establish models for monochrome and color vision. These models may be made quantitative by specifying measures of human light perception. Luminance measures are the subject of the science of photometry while color measures are treated by the science of colorimetry. . PHOTOMETRY A source of radiative energy may be characterized by its spectral energy distribution C X which specifies the time rate of energy the source emits per unit wavelength interval. The total power emitted by a radiant source given by the integral of the spectral energy distribution ftt P 1 C X dk Jc is called the radiant flux of the source and is normally expressed in watts W . A body that exists at an elevated temperature radiates electromagnetic energy proportional in amount to its temperature. A blackbody is an idealized type of heat radiator whose radiant flux is the maximum obtainable at any wavelength for a body at a fixed temperature. The spectral energy distribution of a blackbody is given by Planck s law 1 C X -------C--------- X5 exp C kT - 1 45 46 PHOTOMETRY AND COLORIMETRY FIGURE . Blackbody radiation functions. where X is the radiation wavelength T is the temperature of the body and C1 and C2 are constants. Figure is a plot of the spectral energy of a blackbody as a function of temperature and wavelength. In the visible region of the electromagnetic spectrum the blackbody spectral energy distribution function of Eq. can be approximated by Wien s radiation law 1 C X ----C------ X exp C2 XT Wien s radiation function is plotted in Figure over the visible spectrum. The most basic physical light source of course is the sun. Figure shows a plot of the measured spectral .