[filmscanners] RE: Repeated "Tonal correction", is it god?

["LAURIE SOLOMON" <laurie@advancenet.net>]

A very good and interesting question.  What I offer is my own opinion based
mostly on grounds of theoretical reasoning and not empircal data or
practical experience.  I would say first that I would be reluctant to do my
tonal correction or adjustment at the pre-scanning stage and would tend to
reserve it for the post scan stage.  My reasoning is that I feel that
programs like photoshop not only typically  provide more sophiticated and
better quality tonal adjustment tools than do scaning software applications
but also have means for on the fly previewing and proofing of the
adjustments you are making to the image and its effects or impact while you
are making them which has not been the case with most scaning software
programs that I am familiar with .

Second, I would say that it is ok to do secondary tonal corrections in
either of your cases as long as the second set of adjustments are minor
and/or involved either compressing one or both ends of the tonal range ( the
highlight and/or the shadow portions of the histogram), compressing the
entire tonal range, or compressing the middle portion of the tonal range.  I
would say it is not a good idea to engage in secondary tonal adjustments
that involve major changes or involve expanding previously compressed
portions of the tonal range or the whole tonal range even if it is merelyt
returning those compressed portions to where they were.  If the scondary
need was to re-expand the tonal range or portions of it,I would say it is
better to go back to the original pre-first tonal correction scan and start
all over again from there.

My resaoning is that once one has compressed the range or portions thereof,
one has thrown away the original data such that any re-expansion will result
in the potential for artifacts, noise, generation of erroneous artificial
data ( similar to what can happen with interpolations if one is not careful.
Major tonal corrections after the fact of the first correction can also
result in unintended consequences in part because you have readjusted and
reorganized the tonal balance of the original tonal range such that a
drastic second alteration can create a very unnatural appearing result that
resembles an over-worked painting or charactiture.

As I said that is my opinion and reasoning; others may think and reason
differently or even have experiences to the contrary.  I would be happy to
hear what they have to say and to be enlightened myself on the answers to
your questions.

-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Nagaraj, Ramesh
Sent: Thursday, March 13, 2003 12:07 PM
To: laurie@advancenet.net
Subject: [filmscanners] Repeated "Tonal correction", is it god?


Hi,

I have questions about repeated "Tonal correction" on same file.

case1: Assume that I generate 16bit/Full resolution TIFF file scan from the
scanner.
I do the "Tonal correction" on it using PS and save the file. I find "Tonal
Correction" is so correct, so open the file again and do 2nd round of "Tonal
correction".
Is it bad to do the second round of correction?


case2: My another question is.
If I do the first round of "Tonal correction" at pre-scanning stage using
the scanner s/w so that scanner output is already  corrected.
Then I do 2nd round of "Tonal correction" using PS.
Is this also bad?


Is it recommended to some "Tonal correction" at the pre-scanning phase
itself?

Thanks in advance
Ramesh




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