Photographic Structurometry

the science of the measurement of the imaging properties of a photographic material that are due to the discrete structure of both the undeveloped emulsion layer and the developed image.

Photographic structurometry arose within the framework of sensitometry, and such concepts as graininess and the resolving power of a photographic system were for a long time included in the quantities studied in sensitometric testing. Photographic structurometry did not emerge as a separate branch of photographic metrology until the late 1960’s. At that time, many concepts of general communication theory and information theory were introduced into photography, and photographic material came to be viewed as an element in a system for transmitting, recording, and reproducing images (other elements of such systems may involve the use of, for example, television or electron optics). Terms common to all such elements came to be applied to the description of photographic materials.

In addition to the matters mentioned above, photographic structurometry studies the following: (1) The modulation transfer function. (2) Granularity, which is the objectively measured (with a microphotometer) nonuniformity of the developed image’s optical density D caused by the graininess of the image’s structure. Granularity is expressed by the mean square fluctuation of the density or transmittance. (3) The signal-to-noise ratio; here, the signal is the increment of D in the negative caused by the increment of the exposure from the object, and the noise is the mean square fluctuation of D in the negative. (4) The noise-power spectrum, which is the distribution of the mean square amplitude of the fluctuations of D over the spatial frequencies. (5) The quantum efficiency of detection, which is the capacity of the photographic material to resolve a weak signal in the presence of noise. This quantity is expressed by the quotient resulting from the division of the signal-to-noise ratio in the obtained image by the signal-to-noise ratio in the effective light flux when measured with an ideal detector. (6) The information properties of photographic materials, in particular, the information capacity (the recording density in bits per unit area) and the information sensitivity.