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



Kees,

it seems you mist the main thing about what I said, I can't use charthtrob,
it works only with CS2 and above if I'm not mistaking.

Another thing, many of you propably won't understand this but changing the
color on the neg by which ever mean you like, won't give you the right
density in a single try because the relationship between color and density
is highly unlinear. In other words it is highly unlikely that a single
attempt to bring your print to the right values will work.

Regards,
Yves

----- Original Message -----
From: "Kees Brandenburg" <ctb@zeelandnet.nl>
To: <alt-photo-process-l@usask.ca>
Sent: Saturday, March 08, 2008 5:03 PM
Subject: 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................
>