[filmscanners] Re: Advice on scanner settings

["Preston Earle" <PEarle@triad.rr.com>]

"Arthur Entlich" asked: "Anyone have a good idea how to check two images for
changes against one another such that hue, color, contrast, brightness or
any value change to a pixel would show up clearly as a changed pixel when
comparing two images on top of one another?   I would like to see a
quantitative visual indication of each pixel that is altered by a certain
jpeg setting relative to the non-jpegged tiff."
-------------------------------------

One thought: flatten the "black" image and look at the Levels of that file.
I think you'll find a lot of pixels of 0, 1, and 2 values. I suspect there
will be few pixels of 6 or more value. This will give some idea of the
quantity of changes in the JPEG file. (or maybe 255, etc., values. I never
can remember whether 0 is black or white.)

Second thought: make the "best" print possible of the two files and compare
the two prints. This will give some idea of the quality of the changes. If
you can see the difference in the two files without looking at the files at
200+% on pixel-for-pixel basis, I'd say you've got better eyes than 100% of
other folks in the world.

For really poor slides that need a lot of post processing, I think it makes
sense to start with a TIFF file and convert to JPEG only after all image
correction has been done. For slides where the first scan look pretty good,
I doubt you can do any reasonable changes that would show a difference in
starting with a JPEG or TIFF.

Preston Earle
PEarle@triad.rr.com
www.sawdustforbrains.blogspot.com


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