J. J. DePalma

Sine-wave response of the visual system. I. The Mach phenomenon.

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.

Sine-Wave Response of the Visual System. II. Sine-Wave and Square-Wave Contrast Sensitivity*†

Part I of this series described a method which yielded the sine-wave response of the complete visual system by assuming that the Mach phenomenon is the result of a convolution, in the optical sense, of the object luminance distribution with the effective spread-function of the visual system. This second paper is concerned with measuring the response of the visual system to sine-wave and square-wave spatial distributions using the threshold criterion of contrast sensitivity. Particular emphasis is placed on the low spatial frequencies, a region which is believed to be critically important in the mechanism of visual contrast phenomena. Results strongly imply interaction of two basic mechanisms in the visual system. These mechanisms may be characterized individually as a low-pass filter component (optical) and a high-pass filter component (neural, chemical, electrical, etc.).

Design and synthesis of random phase diffusers

This paper considers diffusers characterized by random variations of optical path, such as ground-glass-surface diffusers. The theoretical limits on the light distributions realizable with random phase diffusers are derived, and the important parameters controlling these light distributions are identified. Methods for generating controlled random signals that, when converted to optical-path variations, have the correct parameters to synthesize diffusers with any desired, realizable light distribution are described. Some goniophotometric data taken from diffusers synthesized by this method are given in support of the theory. These results represent a basic solution of the random-phase-diffuser synthesis problem.

Determination of the Modulation Transfer Function of Photographic Emulsions from Physical Measurements

The modulation transfer function (MTF) of a photographic layer is customarily determined by means of photographic photometry. It is difficult to obtain the true function because of the interference of adjacency effects. De Belder, et al. have recently presented a method of obtaining the MTF from physical measurements of the layer. This method, which utilizes the random-walk technique, simulates the physical processes involved and requires data concerning several physically measurable parameters, including the absorption and scattering coefficients. Data for these coefficients, which De Belder lacked, have been obtained from measurement of the volume reflectance and volume transmittance of the layers by the technique developed by Wolfe, DePalma, and Saunders. The coefficients were calculated by using the Schuster, Kubelka–Munk two-flux, radiative-transfer theory. After the necessary parameters had been measured for several fine-grain silver bromide photographic layers varying in thickness from 3 to 33 μ, the MTF of each of these layers was calculated. These values were compared with the MTF of the layers measured by photographic photometry, when they were developed under conditions giving minimal adjacency effects.Good agreement was obtained between the results of these two methods; the calculated physical values, however, were consistently somewhat higher than the photographic values. At least part of this lack of agreement is caused by halation in the photographic layers from the base-air interfaces.

Measurement of Volume Reflectance and Volume Transmittance of Turbid Media

A description is given of an integrating-sphere-type instrument for measuring volume reflectance and volume transmittance of a thin plane-parallel slab of gelatin having scattering particles embedded within it when uniformly diffuse radiation is incident on the slab. Fresnel surface reflections are eliminated by immersing the slab of gelatin in a liquid matching the refractive index of gelatin. The liquid consists of a mixture of 73% bromobenzene and 27% Nujol Extra Heavy Mineral Oil. The theory of the instrument is outlined.

Quantitative Relation between Chromaticity Differences and Luminance Differences

In general, when two or more stimuli are simultaneously presented to the eye, the phenomenon referred to as “contrast” results. This contrast will be produced by differences between the stimuli, in either luminance or chromaticity, or both.Making use of the fact that veiling luminance, commonly called “glare,” destroys contrast, the authors propose the use of veiling luminance as a means for specifying the equivalence between chromaticity differences and luminance differences. The results of measurements on a large number of samples are presented, together with a practical application of the proposed method to the problem of determining how much chromaticity differences contribute to the judgment of graininess in photographic materials.