Both methods (printing and looking) are too subjective for my taste in
regard to this issue.  I'd really like to see a objective map of the
changes.  My personal sense is that jpeg is much better than most people
give it credit for.

It was designed with human vision in mind, so it does more damage to the
color than the luminosity because we have relatively poor color vision,
but we have good luminosity sensitivity. We are much more aware of
contrast and edge sharpness than subtle gradients of color.


gary wrote:
> How about just changing the opacity and slide between one version and
> the other, and look for differences.
> I don't think printing is as accurate as looking on a monitor.
> Preston Earle wrote:
>> "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

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