NegaFix Expansion Histograms

[Rich P]

I often find that the upper and lower limits of the RGB expansion histograms, when set automatically, are very inconsistent from image to image, even within a series of similar photos, which is leading to very inconsistent, unnatural colour and contrast.

I had in idea which seems to work brilliantly: I make an initial scan of the developed film leader, where half of the frame features only the clear film base and the other half has received 'maximum' exposure when loading the film. This seems to set very sensible limits on each of the histograms and, I believe, equals the maximum possible density range of that negative. (I note another forum user did something similar by exploring the upper and lower limits of each of the frames on his roll.)

I make a note of the numbers and I can then manually set the upper and lower limits to these values and save it as a preset for the whole roll. I am now getting consistent colour and any remaining casts, caused either by the scene itself or from my home development, are easily removed in Photoshop with the Auto Colour algorithm (usually with no further adjustment required).

My question is: does setting the delimiters in this manner have integrity? Am I preserving the true dynamic range, contrast and colours of the film? Are these limits mapped to the upper and lower points of your custom profile RGB curves? It seems to work so I am happy with it but I just wanted to share my method with other users.

Regards, Rich.