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PSYCHOPHYSICAL VISION PROPERTIES For efficient design of imaging systems for which the output is a photograph or display to be viewed by a human observer, it is obviously beneficial to have an understanding of the mechanism of human vision. Such knowledge can be utilized to develop conceptual models of the human visual process. These models are vital in the design of image processing systems and in the construction of measures of image fidelity and intelligibility. | 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 2 PSYCHOPHYSICAL VISION PROPERTIES For efficient design of imaging systems for which the output is a photograph or display to be viewed by a human observer it is obviously beneficial to have an understanding of the mechanism of human vision. Such knowledge can be utilized to develop conceptual models of the human visual process. These models are vital in the design of image processing systems and in the construction of measures of image fidelity and intelligibility. . LIGHT PERCEPTION Light according to Webster s Dictionary 1 is radiant energy which by its action on the organs of vision enables them to perform their function of sight. Much is known about the physical properties of light but the mechanisms by which light interacts with the organs of vision is not as well understood. Light is known to be a form of electromagnetic radiation lying in a relatively narrow region of the electromagnetic spectrum over a wavelength band of about 350 to 780 nanometers nm . A physical light source may be characterized by the rate of radiant energy radiant intensity that it emits at a particular spectral wavelength. Light entering the human visual system originates either from a self-luminous source or from light reflected from some object or from light transmitted through some translucent object. Let E X represent the spectral energy distribution of light emitted from some primary light source and also let t X and r X denote the wavelength-dependent transmissivity and reflectivity respectively of an object. Then for a transmissive object the observed light spectral energy distribution is C X t X E X 23 24 PSYCHOPHYSICAL VISION PROPERTIES FIGURE . Spectral energy distributions of common physical light sources. and for a reflective object C X r X E X Figure shows plots of the spectral energy .