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 -----
From: "Christina Z. Anderson" <zphoto@montana.net>
Sent: Thursday, March 06, 2008 4:13 PM
Subject: Re: curves and gum and Christopher James
book > > 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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