In order to develop a complete specification for the appraisal of the quality of a photographic system by the use of sine-wave response functions, the sine-wave response of the complete visual system must also be known. A method has been worked out for determining the above-mentioned response of the eye. Whenever the eye views a diffuse luminous boundary in which a sudden change of luminance gradient occurs, a bright line appears at the junction of the gradient and the higher luminance, and a dark line at the junction of the gradient and the lower luminance. This phenomenon is a purely subjective one, because physical measurements of the luminances involved show no luminance higher or lower than the two between which the gradient exists.
A visual slit photometer has been built with which the subjective intensity distribution may be evaluated directly. By application of Fourier analysis, the objective and subjective intensity distributions have been combined to yield the sine-wave response of the visual system.
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