From: Bob and Carla (bb333@earthlink.net)
Date: 09/21/02-09:58:10 PM Z
Mark et al.....
Speaking of Photoshop in different purposes....
In my trade, (digital prepress for lithography) there are many
options in Photoshops "page set up" dialog which we never want the
customer to utilize, such as transfer function, screening, etc.,
because they might conflict with the things that are being done at the
"RIP" (raster processing level). I have seen designers supply files
that have had custom screening patterns applied to the Photoshop
files, and they caused moires which required extra billable work to
open all of the files to turn these options off. Same with the
"transfer function" option. The workflow in 4 color lithography
assumes that the photoshop files are final masters, after the
under-color removal, unsharp masking, and color proofing cycles are
complete and that they are "perfect". The screening and trapping and
imposition are all done at the RIP stage, which is when the images and
pages are being raster-processed into data that the computer uses to
actually plots the imagesetter film, or (in the more modern plants)
the actual metal plates that go on the presses.
When we are talking about using Photoshop for making digitally
enlarged negatives, this is where the options in the page setup, such
as "Transfer Function" are really valuable... If anyone is using the
"Curves" or "Levels" dialog to make custom curve adjustments to your
file to match it to your emulsion/paper base/device, you are making
semi-permanent changes to the histographic profile of your image. For
example; if you increase the contrast of your image using Curves or
Levels, you are reducing the tonal steps from (let's say abitrary
figures) thirty-thousand steps to twenty-thousand steps...and save
that change to the file, you are removing the tonality in that slope
permanently. What I mean is that if you want to change it back to a
curve that resembles the one that was made with thirty-thousand steps,
you are not returning to the same data, but are re-plotting that
characteristic curve with interpolated data, because you threw away
ten thousand steps of the optical data. This is where the "Transfer
Function" is really valuable...If you load a profile, or a custom file
in the Transfer Function, it is a temporary curve that can be turned
on for any device. So if you have a Photoshop file that you consider
to be a Master...that is it is at its premium state as a photoshop
version of your photograph, you can print a custom-profiled version of
it to any device (lets say you previously printed to an Epson
Photo-Stylus 700 and you just bought a new Epson 1280, but you are not
changing the material from Pictorico OHP) all you need to do is to
"load" the correct profile for the device (ie; 1280_Orange_OHP) that
you decided makes the best neg on that device, and re-save it with a
name that reflects that profile, and there is no "permanent" change to
your master file... You can the file for the device with that specific
profile. That "master file is still one that you can send to a
lithographic printing company for printing your latest monograph, "The
Seven Bell Peppers of Times Square". I don't think that it matters
when you make it negative...you can filp/flop that, all day long.
Bob
Ender100@aol.com wrote:
>
> This may be a dumb question, but I would be interested in knowing if people
> are applying the adjustment curve to their Photoshop file before they invert
> the image to a negative or after they invert the image to a negative.
> Especially interested in Dan's response.
>
> I assume it would take a different curve for one workflow or the other. Any
> reason one would be better than the other?
>
> Thanks!
>
> Mark Nelson
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