Hans J. Zweig

On the Information-Detecting Capacity of Photographic Emulsions*

The concepts of quantum efficiency and detecting capacity of photographic emulsions are discussed with reference to the granularity, spread function, and characteristic curve of the emulsion. A measure of informational sensitivity is introduced which depends on these quantities and provides an objective measure of performance of emulsions when they are compared at their optimum working scales. In terms of this measure, as well as from a direct visual appraisal of picture quality, it appears that two emulsions, such as Kodak Tri-X Film and Kodak Panatomic-X Film, can have widely different sensitometric speeds but quite similar informational sensitivities.

Autocorrelation and Granularity. Part I. Theory

The applicability of time-series analysis to microphotometer traces is developed with particular reference to two proposed measures of photographic granularity. It is shown that two equivalent functions may be obtained from a microphotometer trace—a correlogram and a power spectrum—and that both Selwyn’s measure of granularity depending on density dispersion σD, as well as Jones and Higgins’s measure depending on syzygetic density difference 〈SΔD〉Av, are directly related to these functions. The conditions under which these measures are equivalent are pointed out.

Theoretical Considerations on the Quantum Efficiency of Photographic Detectors

The relation of theoretical characteristic curves for monolayer ensembles of go-no-go detectors (emulsion grains) to quantum efficiency is developed. It is shown that the statistical fluctuations in the incident photons, as well as the fluctuations in the number of detectors made developable by a given exposure, preclude the possibility of achieving a quantum efficiency of unity. The maximum quantum efficiency achievable depends on the number of photons required for developability as well as on the exposure. The latitude requirements for such an ensemble impose further restrictions on the achievable quantum efficiency.

Relation between Graininess and Granularity for Black-and-White Samples with Nonuniform Granularity Spectra*

In order to determine the relation between the visual impression of graininess and the objectively determined granularity of a wide range of granularity types, a series of samples was prepared containing uniformly exposed black-and-white materials and prints (transparencies) containing varying degrees of mottle. These samples were judged by the method of paired comparisons at different magnifications and scanned to obtain the standard deviation σ(D) for a wide range of scanning apertures. The psychophysical relationship between the two functions, (1) graininess versus magnification and (2) granularity σ(D) versus the square root of the scanning area, depends on the character of the scanning operation performed by the eye. An estimate of the size of the effective scanning spot of the eye can be obtained from these data.

Autocorrelation and Granularity. Part II. Results on Flashed Black-and-White Emulsions*

The relation of Selwyn’s granularity measure to the character of the autocorrelation function and the granularity spectrum is discussed. The shape of the autocorrelation function as experimentally obtained leads to the conclusion that Selwyn’s granularity function σD·d should be essentially constant and independent of d. The fact that it is found to increase with d can be explained by (a) the existence of macroscopic variation in density (which can be largely eliminated) and (b) a combination of finite grain size and imperfect imagery. Jones and Higgins’s data on the perception of graininess are combined with the present data on granularity to provide a measure of granularity for uniformly flashed black-and-white emulsions, which is approximately independent of the area of the scanning spot and the density of the sample.

Autocorrelation and Granularity. III. Spatial Frequency Response of the Scanning System and Granularity Correlation Effects Beyond the Aperture

It is shown experimentally that, although the granularity correlogram of a uniformly exposed and developed black-and-white photographic emulsion ordinarily extends only over a correlation distance equal to the diameter of the scanning aperture, correlation is exhibited over significantly greater distances when clumping is produced, e.g., by exposing to x-rays or developing to a high density. The difference between the effects produced by large and small scanning apertures is discussed, and it is shown that the variance for one aperture size cannot always be predicted from the variance for another. The procedure for combining the correlogram of a negative as affected by the printing procedure with the correlogram of the positive stock to give the correlogram of the print is discussed with examples. In the appendix, it is shown that the ordinates of the correlogram of the negative, as transferred to the print, are proportional to the square of the gamma of the positive stock and to the density of the negative. The importance of knowing the behavior of the microphotometer used to obtain the correlograms is demonstrated by a practical example.

Roles of Sharpness and Graininess in Photographic Quality and Definition

Sensitometrically matched photographic prints were judged by a number of observers for sharpness, graininess, and two over-all attributes that were termed in the instructions “picture quality” and “definition.” The results indicate that the two latter terms had definite meanings for the observers, but the term “picture quality” led the observers to weight sharpness and graininess about equally while the term “definition” led to a high correlation with sharpness and a low correlation with graininess. Both the method of ranking and the method of paired comparisons were used, and they were found to be about equally capable of disclosing inconsistencies.

Effect of Complex Granularity Patterns on the Determination of Quantum Efficiency

AbstractThe Selwyn relation, σ√a=constant, where a is the area of the scanning aperture with which it is measured, has been found to hold for uniformly exposed and processed black-and-white negative materials. When such an image is printed, the large-scale component of negative granularity is added in the print to the granularity of the positive stock, and the combined prmt granularity can be shown to depend on the area of the scanning aperture. The consequences from the standpoint of quantum efficiency are that, when quantum efficiency is most suitably defined and when Selwyns relation holds, it is independent of the area exposed and measured, but when Selwyns relation does not hold, quantum efficiency must be determined from measurements mode with a scanning aperture so large that no larger aperture will give a higher value of σ√ On tins bosis, no quantum efficiency greater than 1 per cent hos been found in photography.