Quote Originally Posted by Donald Miller
Interesting dialogue on this subject. I also do not understand why one would measure the step wedge density in UV mode. The only time that this would appear to be a valid consideration would be when the step wedge exposure on film would be facilitated by UV light.

The step wedge density would seem to be valid when measured by the densitometer channel most closely approximating the spectral qualities of the light that would be exposing the step wedge onto film.

What am I missing here?
The color of the light being used to expose the film is irrelevant. The density could come from red, green, blue or UV light. The color might affect the contrast or density of the test strips but that would make no difference to the plotting.

The key with the plot is that you must have the same measurment of density on the x and y-axis. If not, the curve will be artificially distorted because the units of measurements are of different length on the two axis.