U of S | Mailing List Archive | alt-photo-process-l | Re: curves and gum and Christopher James book

Re: curves and gum and Christopher James book



(boyscouts, yippy,yippy, yť)

first try to find the (aproximate) exposure time to get maximum black for your printing technique through your printing substrate
then find the right blocking colour to get white by using either RNP array or PDN or using Quad Tone Rip en try different inkdensities (Ron Reeder method)

Run charthtrob

Chartthrob samples the centre part of each patch of the101 step grayscale and blurs it to get an average value and then compares it with the input values to get a correction curve. This is the curve you have to apply to your positive, and then invert it and print it

ready, go, print!

-k


The technical reason why both methods can get away by using the
linearisation thing is rather complicated but I'll try to explain it as
simply as I can. When you are ask to measure a step of a step wedge on an
alt-print, say the scan print is on screen and you move the mouse over the
step, the value, values in fact are all over the place and you are forced to
average out those variation by some mean. But this means implies a serious
problem, say we make a small square image and we give it the color red
(255,0,0), if you move the mouse over this square you will have the same
value where ever the mouse is over the square, right. Then you print this
square image on a transparent material, Pictorico or whatever, then you scan
this transparent and open it, if you move the mouse again over the square
you will see that the value(s) is nothing but uniform again, this is because
the printer prints dots of ink, not of a red color but of various ink colors
and your good scanner picks up all those tiny variations. Next if you would
use this colored square as a negative to make an alt print, and make a scan
again you would see the values going even more over the place. The average
over the alt print square maybe a single number but the reality is that the
actual values are spread both under and above this number. We start with a
single value, say 127 on our original and it gets printed as severals on the
alt-print, a value close to 127, say 130 will also translate into severals
and it is almost certain that you wont be able to disthinguish between the 2
most of the time. All this to say that the linearisation problem is hidden
by this spreading of values it doesn't mean it's not a problem. Knowing this
and say I like my original subtle variation in the clouds or where ever, if
you don't do something to compensate for these combined problems, you can be
assured these subtilities will be lost in your alt-prints.

This is also the reason why I say that each original as to be treated
individually, some will need compensation in the highlights, some in the
shadows, etc. These compensation will depend on the process used, the
materials used, especially the paper and on your habilities to be consistant
in your workflow.

Some folks will say this is ART, ok it's fine, live long and prosper, but I
suspect these folks have learned all this intuitively and it's become a
second nature for them to treat each image differently to give it some SOUL
as they say.

Which ever way you look at it, these systems are all but TECHY, it's still
very close to the trial and error approach.

I'll add I never said they are not usefull, I'm just saying they are not
HITECH, nothing more nothing less.

Regards,
Yves


----- Original Message -----
From: "Kees Brandenburg" <ctb@zeelandnet.nl>
To: <alt-photo-process-l@usask.ca>
Sent: Saturday, March 08, 2008 5:22 AM
Subject: Re: curves and gum and Christopher James book


Yves, did you ever try chartthrob? That  allready comes close to the
first part of your 'program wishes'.

http://www.botzilla.com/blog/archives/000544.html

http://www.inkjetnegative.com/images/RNP/quick_guide_to_making_digital_ne.ht
m
kees

Here is an idea of the kind of tool most computer nerds like me would
consider hitech. Let's say we have determined the exposure time at
another
stage. One would make a single test print (1) and make a scan of it,
you
then give this scan to a program which would read the scan and extract
information from it automatically................