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Don.
basically it fails to reproduce local contrast as
well as other characteristics of the original amoung which there is a potential
for loosing details. If you have time take a look at Reinhard introduction
(http://www.cs.ucf.edu/~reinhard/papers/tvcg2005.pdf) it's only
a page and he explain all this in plain english (I think) much better then
I can.
Unfortunatly, PS doesn't provide any direct help
for this. A simplistic work around would be to compress the original range
to the range of possible print values using a strait line "curve" for
exemple and while maintaining these limits apply other
transformations in an attempt to recover the original image
qualities. The tone mapping operators have parameters you can adjust which
means the transformation can be done creatively.
In case there are Photoshop programmers around,
there is a library called FreeImage which provide the 3 operators I mentioned
below amoung other tools.
Regards,
Yves
----- Original Message -----
Sent: Thursday, March 06, 2008 11:28
PM
Subject: Re: curves and gum and
Christopher James book
Yves
Does the research by Reinhard & co tell us
that simply re-mapping a range of tones on the basis that
each original value always corresponds to the same compressed value
will yield a new image which fails to reproduce local
contrast?
If so, is there a solution available in
Photoshop, or does it require something more complex?
Don Sweet
----- Original Message -----
Sent: Friday, March 07, 2008 12:07
PM
Subject: Re: curves and gum and
Christopher James book
Christina,
it's not a question of being smart or not, I'm
sorry if you find my remarks offensive, it wasn't my intention.
What PDN does to create negative and most
others approach I've seen so far, is they use a curve to map values of the
original to the values of the print in a 1 to 1 relationship. Graphically,
this relation would look like a strait line thus the term "linearised".
The problem with this comes from the fact that it's not possible to get
print values extending the full range of the original values [0..255].
Thus, the range of original values needs to be compressed to
the smaller print range of values. Before making the curve PDN suggest
to expend the range of the scan to [0..255], this is equivalent to
compressing the original range.
Here is a small extract from Reinhard
paper.
"This leads to
the problem of how to display high dynamic range data on low dynamic range display devices, a problem
which is generally termed tone mapping or
tone reproduction [3], [4]. In principle this
problem is simple: we need to turn an image
with a large range of numbers into an image containing integers in the range of 0 to 255 such that we can display
it on a printer or a monitor. This suggests
linear scaling as a possible solution.
However, this approach is flawed because details in the light or dark areas of the image will
be lost due to subsequent quantization, and the
displayed image will therefore not be perceived the
same as the scene that was photographed"
Before anyone says this doesn't apply to
prints, I would add, in the case of prints, the display device range
[0..255] needs to be compress to an even smaller range then that. This is
true for any alt-process prints and for silver prints as well, there is no
way around this fact.
I understand many gum printer use the process
"creatively" and this is very diffirent then using a print process to
reproduce an original image. This is why I dare say that from the point of
view of reproducing an image, the PDN approach is very simplistic and there
is nothing techy or precise about it.
Some will say that in the absence of a better
solution, PDN is possibly the best solution around and it maybe
so for now. But when I ear praise for PDN I can't help myself to think
if they only knew, it's a shame.
It's unfortunate that I have a bad healt,
otherwise I would work on this myself and offer it for free beside
that. The tools and knowledge to do it right are out there, I know
I did some research on this.
I hope this clarifies things a
bit.
Regards
Yves
----- Original Message -----
Sent: Thursday, March 06, 2008 4:13
PM
Subject: Re: curves and gum and Christopher
James book
> Ohhh Yves,
>
> A) I have no idea what you are
talking about
> B) I do not teach digital
> and
> C) I am
apparently not anywhere near as smart as you.
>
> But thanks
for the thought!
> Chris
>
> ----- Original Message -----
> From: "Yves Gauvreau" <gauvreau-yves@cgocable.ca>
> To: <alt-photo-process-l@usask.ca>
> Sent: Thursday, March 06, 2008 1:29 PM
> Subject:
Re: curves and gum and Christopher James book
>
>
> >
Christina,
> >
> > I find it very strange that a
University professor finds that linearized
> > tone mapping is
hitech when it's in fact the worst approach one can use.
> >
It
> > is as if you never eard of Tone mapping operators (Adaptive
logarithmic
> > mapping (F. Drago, 2003), Dynamic range reduction
inspired by
> > photoreceptor
> > physiology (E.
Reinhard, 2005), Gradient domain High Dynamic Range
> > compression
(R. Fattal, 2002) and others)
> >
> > Yves
>
>
> > ----- Original Message -----
> > From: "Christina
Z. Anderson" <zphoto@montana.net>
>
> To: "Alt, List" <alt-photo-process-L@usask.ca>
> > Sent: Thursday, March 06, 2008 10:06 AM
>
> Subject: curves and gum and Christopher James book
> >
>
>
> >> Hi all,
> >> I am so thrilled with
Christopher James' new edition of the Book of Alt
> >>
Proc. I'm not going to go into all the reasons why, just buy it you
> >> won't
> >> regret it. Besides, it's got
3 Judy Seigels in there as well as Dan
> >> Burkholder's piggies
and Sandy King and probably more names otherwise you
> >> all
would recognize--can't say you don't get your money's worth from the
>
>> images therein!
> >>
> >> Anyway, we've
talked off and on about curves and gum, about different
> >>
negatives and gum, etc. etc. As we have probably always concluded,
gum
> > will
> >> suit itself to whatever practice is
chosen, and there are many ways to
> > skin
> >> a
cat.
> >>
> >> Lately I have been working with a
variety of negative choices to compare
> > my
> >>
practice (tricolor seps with individual PDN derived curves and colors
for
> >> each neg) with other lesser techy ways to teach
students who may not have
> >> Photoshop or even know what a
curve is. Bitmap, all ink negs, CMYK,
> > pulling
>
>> a curve out of my butt/on the fly...I have changed my teaching
practice,
> >> even, at MSU, to start the students with all inks
greyscale neg one coat
> > gum
> >> first, then a Sam
Wang duotone negative next (greyscale, no curve, all
> >>
ink
> >> neg), then an all inks tricolor third (no curve) and
finally they will do
> >> the grandaddy of them all, making a
custom curve PDN Mark Nelson
> >> tricolor.
> >> I
find that starting students out low tech and moving to high is a way
to
> >> "hook" them into the process.
> >>
>
>> So when I saw the gum curve of Tony Gonzalez in James' book I about
died.
> >> It is hilarious. I mimicked it on my computer
and found that the range
> >> of
> >> tones he has
in it go from about 26 to 92! He has essentially clipped
>
>> almost 200 tones! It looks like a flatline/dead person
curve. However,
> >> THEN look at his gum print (curve p.
351, gum p. 352-3)! The proof of
> >> someone's working
process is ALWAYS in the pudding.
> >>
> >> I will
try Gonzalez' curve but what I bet I will find is that I have to
>
>> alter other parts of my practice to fit into the curve, whether it
be
> >> pigment load or development time or dichromate amount or
exposure time or
> >> whatnot. The reason I bring it up is
that as I tell my students, gum is
> >> really not a
photographic process. If you did a curve like that with
> >
pt/pd
> >> you'd have posterization and a gross print, but with
gum which is just
> >> hardening a layer where it needs to
harden, it just isn't the same (e.g.
> > you
> >> can
choose an exposure time of 1 min vs. 8 minutes and get a thinner or
>
>> thicker layer of hardening which is not possible with BW printing
or even
> >> pt/pd--certainly not as much variability.)
And Gonzalez looks like he is
> >> just squushing all his tones
into the narrow range of stops that gum
> >> represents, being a
shorter scale process than other longer ones like
> >
pt/pd.
> >>
> >> It looks like Gonzalez teaches at
Queens College, CUNY so if he ever has
> > an
> >>
exhibit I would run to it. Anyone on the list know him? I wonder
if he
> > was
> >> a student of Sarah Van
Keuren's?
> >>
> >> So check out the book--it'll
definitely spur the creative alt juices
> >> going
>
>> with the images alone, much less the information.
> >>
Chris
> >>
> >>
> >> Christina Z.
Anderson
> >> Assistant Professor
> >> Photo Option
Coordinator
> >> Montana State University
> >>
CZAphotography.com
> >> _______________
> >>
>
>>
> >
> >
>
>
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