Profiling verification
Profiling verification
- Subject: Profiling verification
- From: ross lists <email@hidden>
- Date: Sat, 19 May 2001 18:34:49 +0100
Hello,
I would like to take an opportunity to raise a few points regarding what
some may see as basic points regarding ICC profiling.
A brief description of our chosen workflow.
Files from different digital cameras are converted into Adobe 1998 RGB using
generic and custom profiles. The files are viewed in a subdued daylight
enviroment on Lacie electron monitors calibrated and profiled using
colorblind Prove it and a Spectrocam. Guide prints are produced on an Epson
1270 using an RGB linearisation and profile produced by Colorblind Matchbox
plus and viewed in a D50 viewbooth.
[We have also tried to output using press ready but can make no sense of the
printing route or the many dialog boxes one has to go through and get no
meaningful output, the calibration bars on the print always have a cast.
We've tried to put a custom profile in PressReady.]
We achieve a good match between the screen and the subject so we feel that
within the limitations imposed by the monitor colour space we have a good
representation of the file. I conclude the RGB file is neutral, the numbers
on the grey scale of the macbeth chart agree. So if the ICC workflow allows
an accurate screen preview why do the results - when moved to a printer or
separated to CMYK - look flat and the colour is wrong, even the greys do not
remain neutral.
I know that we can tweak the file or the profile visually, but how do we
know what we are seeing is accurate.
*****
Here is the nub. Can any of you suggest an approach to checking the
integrity of this process that is empirical i.e. based on readings using the
colour picker and the spectrocam.
*****
I propose to use a Macbeth chart and produce a file in adobe RGB from a LAB
file produced using the published values and direct readings then compare
that to the print and the screen. Can the spectrocam be used to read the
values from the monitor to check the values?
Being cynical for a second, isn't that how ICC profiling works.
I know I have missed out some vital information and will supply it on
request. I wonder if there are others out there whose direct experience of
profiled workflows does not gel with replies made to questions on the list
but whose ignorance may lead them to keep quiet?
Look forward to hearing from you all.
Ross
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Ross Kerridge
Imaging Systems Director
Photolink
http://www.photolink.co.uk
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