Source to Destination RGBCMY
Source to Destination RGBCMY
- Subject: Source to Destination RGBCMY
- From: Joel <email@hidden>
- Date: Fri, 28 Sep 2001 09:33:37 -0500
Relative, but not absolute, to One Shot Profiling.
Background:
Roland FJ500 profiles generated on the PC (PhotoPrintServer v2.6.1 w
ColorCal) sets the Preferred CMM to Lino and Default Rendering Intent
to Perceptual. Currently I use Colorthink to change both to AppleCMM,
Relative Colormetric respectively and print from PS6.0.1 for our fine
art reproduction workflow.
My profile building procedure is based mostly on reading various
materials from other applications available on the web and putting
the pieces together (because the provided manual ends at How to...).
Procedure:
Print ink limit target.
Visually estimate ink limits.
Test Tdensity range of ink limit with CM2s spectro.
Print and measure linearization target with CM2s spectro.
Print and measure XYZ target data (yes with CM2s!).
Leave GCR at Medium.
Leave Ink Limit at 400 or the application's offered value.
Black Ink Start at 0.
Black Ink Limit sets itself according to Ink Limit and linear curve adjustment.
Generate profile with Large LUT and PreviewTags ...and voila, I have
a profile! Performs OK but there is better...
Dilemma:
There is this advance procedure called Color Mapping which I call editing:
This menu provides Source Color lab values (CIELAB as best I can
determine) for RGBCMY respectively, and allows the user to change
Source Colors to Destination Colors as individual inks (in this case
CMYKOGLcLm) or as Lab values (with Out-of-Gamut alarms).
(I am thinking this an A2B2 thing - any reference reading material
suggestions appreciated here.)
If I push DLab to equal SLab regardless of alarms I get better
onscreen previews during softproofs and conversions than any provided
canned profiles.
If I tweak DLab to the edge of the SLab gamut alarms only, I still
get better onscreen previews during softproofs and conversions than
any provided canned profiles.
The major difference between the two, DLab=SLab has better blacks.
If I edit from Source Lab RGBCMY to ink tables based on ink limits
two points are worth noting:
1. The application seldom if ever defaults to using O, G, Lc, or Lm.
The majority default is CMY only and less than 6 K.
2. If I edit to Lab then look at ink table the extra inks come into play.
Question: Can anyone tell me what I am editing? The results are worth
it, but I'm a little blind as to why?
(Mapping the defaults against the edits in Colorthink reveals
identical 2D and 3D spaces.)
TIA
--
joel johnstone - designtype
Winnipeg Manitoba Canada
(2B Aknot2B, that is the question)