Wrong Processing

Dan Margulis <76270.1033@...>

Tony writes,

Is there any proved and tested approach for correcting colour and density
errors caused by film being wrongly processed? eg colour neg film processed
thru E6 or tranny film procesed thru C41 chemistry.>>

The generic answer is that it's the same as if the photographer used a
grossly incorrect exposure originally.

Everything will depend on what exactly the screwed-up process did to the
image, but there are a couple of things that suggest themselves more than
with other kinds of images.

First, LAB corrections are more likely to be appropriate here. They can
correct gross color casts. Also, whatever cast the process puts in is
likely to be a uniform one. The disadvantage of LAB is that it can't deal
with countercasts, which won't be a problem here.

Second, if the image is really poor after the scan, consider changing your
RGB working space definition momentarily. These kinds of errors often
cause not only an incorrect darkness but also a lack of saturation. So it
can be helpful to put in a false working space definition, say Adobe RGB
primaries with a much lower gamma than usual, before converting the RGB
file to LAB.

The bad news is that a lot of expertise can be required, the good news is
that once you have figured out what needs to be done, usually that can be
scripted and you can just run the script on the rest of the batch.

Dan Margulis