The contrast of photographic printing paper

Abstract

The results obtained in Section B may be summarized as follows: 1. (a) The brightness contrast in the object chosen as a “typical landscape” (Fig. 5) was found to be 39, the highest light having a brightness of 2500 millilamberts and the lowest 64 millilamberts. 2. (b) A panchromatic material was used in making the required negatives in order to minimize the distortion of the visual tone relations due to color effects. By developing a series of sensitometric strips the time of development required to give any desired gamma was determined. The curves obtained show that the exposure latitude of this material is 35, whjch is approximately sufficient for the rendition of the entire object on the straight line portion of the characteristic curve. 3. (c) A group of nine negatives was made, each having identical exposures, the development time being varied to give gamma values ranging from .38 to 1.32. The densitometric characteristics ( D max., D min., and γ) of these negatives were determined by density measurements made directly thereon and by density measurements made on sensitometric strips developed with each negative. 4. (d) Using the negatives thus obtained groups of prints were made from the appropriate negatives on thirty-seven different developing-out papers selected to cover the entire range of contrast available in materials of this type. From the prints made on each developing-out paper judgement was made by seventy-five observers on the negative producing the optimal photographic quality. The data thus obtained have been examined critically, and from it certain conclusions have been drawn relating to the characteristics of the observers, the repeatability of judgments of print quality, and the average photographic quality considered as optimal by observers differing radically in their training for the judgment of print quality. li ](e) A summary of the statistical data thus obtained is given, from which is obtained the gamma of the optimal negative for each of the developing-out papers used. The probable error to be remarkably small and indicates that these values may be relied upon as truly indicative of the negative quality which will give the best possible print of the particular test-object used in this work on each of the positive materials. 5. (f) From density measurements made directly on the positives, values of maximum and minimum density for the optimal positive are derived, the difference between these giving the density scale for the optimal positives. These values relative to the optimal positives, together with the densitometric measurement relative to the optimal negatives, constitute the data from which, in connection with the sensitometric data to be obtained in the following section, values of contrast for the positive materials are computed.