Color Management in Fierys for copiers (1 of 2)
Color Management in Fierys for copiers (1 of 2)
- Subject: Color Management in Fierys for copiers (1 of 2)
- From: David Macy <email@hidden>
- Date: Mon, 8 Oct 2001 10:02:19 -0700
Since there seems to be a lot of confusion on what ColorWise does in the
Fiery, and whether ColorWise is "true ICC color management", I'd like to
present some information which I hope will be helpful. I will discuss
ColorWise 2 which is shipping in virtually all Fiery systems today, then in
the folowing email (since this one would be too long to post) present some
new features of ColorWise 3 which was announced at Seybold and will begin to
ship soon. Because the Epson inkjet printers with their RGB model have their
own distinct feature set, I will not include those printers in this
discussion - instead, I will focus only on CMYK devices such as color
copiers.
ColorWise is a true ICC based color management system.
ColorWise allows the user to install ICC profiles representing RGB monitors,
scanners or RGB working color spaces (EFI calls these "RGB Source
Profiles"); CMYK printers not attached to the Fiery or CMYK working color
spaces (EFI calls these "CMYK Simulation Profiles"); and CMYK printers
driven by the Fiery (EFI calls these "Output Profiles").
Following is a description of the color data flows in the ColorWise.
++++ For RGB input:
[RGB Source Profile] -> PCS -> [Output Profile]* -> Calibration
or
[RGB Source Profile] -> PCS -> [Simulation Profile]* -> PCS -> [Output
Profile]# -> Calibration
+++++ For L*a*b* input:
L*a*b* -> [Output Profile]* -> Calibration
or
L*a*b* -> [Simulation Profile]* -> PCS -> [Output Profile]# -> Calibration
+++++ For CMYK input:
[CMYK Simulation Profile] -> PCS -> [Output Profile]# -> Calibration
or
CMYK -> Calibration (if "CMYK Simulation Profile: None" is selected)
or
CMYK -> Printer (if "CMYK Simulation Profile: Match Copy" is selected - only
available from ppd)
+++++ For Spot (named) Color input:
[Named Color Profile] -> PCS -> [Output Profile] -> Calibration
or
Alternate Color Space -> CMYK path (if alternate color is CMYK)
* (uses specified Rendering Intent)
# (uses specified Simulation Method)
+++++ Why do some people think that ColorWise is not a true ICC system?
One area where it may appear that ColorWise is not using ICC profile data is
in the CMYK -> CMYK conversion based on the CMYK Simulation Method. The
simulation methods in ColorWise 2 are "Full" and "Quick".
Full Simulation performs color space conversion based on the color data in
the ICC profiles, but has a somewhat unique approach in that it preserves
the Black channel. Because of this black preservation, some profiles which
have been modified using a profile editing tool will produce different
results than they will with other CMM's. I think this is one of the main
reasons that some customers incorrectly assume that ColorWise is not using
ICC profiles.
Quick Simulation uses a set of 4 transfer curves which are derived from the
relationship between the Simulation Profile and the Output Profile. This
method is not performing true color space conversion, simply simulating
based on tone response.
The Second common point of confusion is the use of the Output Profile. As
you can see above, an Output Profile can be used to affect all source color
data, but in certain cases, the user can choose to bypass it. Some incorrect
statements on this list have indicated that the Output Profile can never be
turned off and therefore the system cannot be profiled. In fact, ColorWise
allows the user the flexibility to either completely bypass ALL color
conversion and calibration by sending CMYK data to the Fiery and selecting
"CMYK Simulation: Match Copy", OR to bypass all color conversion but still
use calibration by selecting "CMYK Simulation: None"
Why use None vs. Match Copy? Printed densities on color copiers tend to
drift over time. Profiles describe how a device behaved at a specific point
in time. Calibration attempts to bring the device back to the state it was
in when the profile was made. It is usually faster and easier to calibrate
frequently than to profile frequently, so we recommend that people make
profiles in a known, calibrated state, then use the calibration procedure to
ensure that the device behaves in the same way over time.
In ColorWise Pro Tools, we display a diagram of the color processing in the
system, including which profiles are used for each type of input and color
management selection. This diagram indicates that even for Simulation: None,
the output profile is used. While this is true, in this case ONLY the
calibration state information (also known as Target) which is stored in the
output profile is being applied. No color conversion is taking place. So,
CMYK Simulation:None is the best selection to use when you are making a
profile.
to be continued...