|
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
> >>
_______________
> >>
> >>
> >
> >
>
>
|