The Childress Process of Correct Tonal Reproduction.

The density-log exposure curve of normal black and white silver haloid emulsions is composed of a straight line section of desired contrast bordered on each end by a curved section of insufficient contrast. The fact that both negative and positive emulsions have these same characteristics, makes it impossible to obtain perfect photographic tonal reproduction from an original without masking. Assuming the sinus shaped characteristic curve of the positive emulsions as unalterable, it follows that the corresponding negative material would have to be processed to a mirror curve to achieve correct tonal reproduction in the final print. A film processing method which produces negatives with mirror curve characteristics is described and discussed with special consideration of its applicability to photogravure.