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PROCESSING MOTION PICTURE FILM
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It is obviously necessary that emulsion manufacturers should produce materials which, over a large portion of their range, react proportionally so that steady increases in log-exposure time produce correspondingly steady increases in density. The actual increases in density which result from unit increases in logexposure depend upon the slope or 'gamma' of the proportional section of the curve which represents the characteristics of each film under given processing conditions.
In Figure 57 three straight lines, 'A', 'B' and *C\ are used to represent the proportional or 'straight line* sections of the characteristic curves of three different emulsions processed under similar conditions or, alternatively, of one emulsion processed under three different conditions. Since all three lines intersect at a single point we see that, in all cases, a density of 1 0 is produced when a log-exposure time of 1 -05 is given. However, a density of 2 -0 is produced by the conditions represented by line 'A' when a log-exposure of 1 -65 is given, whereas this density is only produced by line 'B' when the log-exposure is increased to 2 -05 or, by line 'C\ when it is increased to 2 -55. It is very important to remember that, under all three conditions, steady increases in density at any point throughout the range will be obtained by correspondingly steady increases in log-exposure. That is to say, all the emulsions are reacting proportionally over these sections of their characteristic curves.
LOG EXPOSURE
Fig. S7. — Various degrees of contrast expressed -graphically