Checkerboard grain which simulates photographic grain can be used to demonstrate the basic concepts of the effect of grain on resolving power. Images of gratings have been imbedded in checkerboard grain which the eye cannot detect. The contrast threshold for such gratings is many times higher than for ordinary gratings. The viewing distance or magnification has a marked effect on the visibility of such gratings. If the magnification is too high the eye cannot assess the average brightness of a grainy patch, and if it is too low the eye cannot resolve the lines of the grating. A photographic reproduction of the Washer–Rosberry resolving power test chart has been analyzed and it is shown that grain size per se is not the limiting factor for resolving the grating. A more important factor is the spread of the image which reduces the contrast between the light and dark bars of the grating and transforms square waves to sine waves. A method is proposed for testing combined effects of grain coarseness, average transmittance, line spacing, and contrast on the visibility of sinusoidal gratings.
© 1963 Optical Society of AmericaFull Article | PDF Article
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