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

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

Austin,
You have me laughing.  We are in substantively complete agreement in
everything you have said.  My responses were tailored to the original
questions posted and the later one posted.  Originally, the two main
questions dealt with is it bad or inadvisable to engage in tonal corrections
to a file that has already be tonally adjusted or corrected previously and
is it better to do the initial tonal correction in the pre-scan stage witht
he scanner software or in post scan stages using PS.  Later the question was
how does bit depth relate to tonal range.  At least that is how I read the
questions.

The one thing that I did not attend to was if ones printer can print the
result that one gets or if it serves as another limiting factor.  I agree
with you that for all practical purposes it presents a limiting factor and
constains the sorts of tonal ranges that one can capture such that many
advantages of an expanded tonal range and many of the corrections and
adjustments may not be of any practical consequence in terms of showing up
in the printed output.  However, this does not preclude the possibility that
expanding via tonal correction of a previously compressed - by a previous
tonal adjustment - area in the tonal range might create artifacts and noise
that could be captured and reproduced or show up in the printing.  This was
one of the points that I was attempting to make about secondary adjustments
to previously adjusted tonal ranges.  The other main point was that there
were in my opinion practical resons for selecting to do tonal adjustments
post scan in Photoshop (I assumed in making my remarks that the bit depth of
the scan was the bit depth of the file that was being adjusted and that it
had not for example been originally scanned at high bit depth and then
converted to 8 bits per channel prior to tonal adjustments being made after
the scan.

With respect to the second posted question, the main points I was making,
you say below you agree with.  So I am thinking that we are now talking past
each other rather than to each other.  The one question which neither you or
I (or anyone else for that matter) has answered is the one in the Subject
Line of the thread : "is it god?"  I have no answer to that.  Do you?

-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of Austin Franklin
Sent: Thursday, March 13, 2003 9:18 PM
To: laurie@advancenet.net
Subject: [filmscanners] RE: Repeated "Tonal correction", is it god?


Hi again, Laurie,

> To put words in shAF's mouth (hope you don't mind shAF), the use of a
> greater bit depth - 16 bits/channel rather than 8 bits/per
> channel - allows
> one to capture a much more expansive tonal range rather than the more
> compressed range of an 8 bit per channel capture.

That is correct...but...

> This means you
> will have
> more tonal detail and subtlties available within the range and captured by
> the data.

That is true as well...but...

> Thus, with a 16 bit scan, you have more tonal
> inforamtion to deal
> or play with; but once you reduce the tonal range by converting
> to an 8 bit
> file or once you have performed your first tonal adjustment, you
> have thrown
> away some of that original data or altered it in a manor that it cannot be
> recaptured by new adjustments or even in many cases reconstructed so as to
> be exaclty as it originally was.

That is also true ;-)...but...

but...can your printing system reproduce all those tones, and if it could,
could you even see them?

You can't tell the difference between printing from an 8 bit file or a 16
bit file for color, and barely is there a difference in B&W.  Again,
remember, for color you have 24 bits, not just 8...so really, working with 8
bit color data is really indistinguishable in most all cases that if you
were to work with high bit data.  I still think you should do any large
tonal correction in high bit data, in the scanner driver and let the scanner
give you 8 bit data, or in PS, and then convert to 8 bit data if you want.

For B&W, you can actually, if you have a really good B&W printing system,
some difference in prints made using high bit data and prints made using 8
bit data.  It is VERY image and system dependant though, and the differences
are really barely perceptible to even the very trained eye, if using
something like Piezography.

Regards,

Austin

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