[Openicc] Introduction / Gutenprint

[Jan-Peter Homann]

Hello Robert / hello list

I will describe, what are my whishes from a view as colormanagement 
consultant, who has profiled printers since 8 or 9 years.


In this mail, I will discuss two main point:

1. Colormanagement in the printer-driver itself
2. color-infrastructure / colorsettings
(Operating-System, application, printer-driver)

1a. good profiles need good linearization
-------------------------------------------
The linearization of the CMYK(cmRGB..) chanels is the basis for 
printers-colormanagement which works.

Linearization is mainly done with 1D Luts for each channel. During 
linearization, the user sets an inklimit for every single channel and 
generates / manipulates an curve from zero-color to the inklimit.
This 1D Luts can be generated via an graphical interface like a 
gradation curve, or they are calculated by measurement with an 
densitometer / spectrophotometer like the GMB EyeOne.
Also necessary is an total-inklimit for all channels together.
This inklimit is done by replacing equal CMY-amounts with K, also known 
as GCR. The optimal total-inklimit is visual evaluated from testprints 
with special images for inspection of inklimits.

After linearization / inklimiting, the testchart for profiling will be 
printed.

1b. ICC-colormanagement
------------------------
ICC-based colormanagement transforms the colordata from the 
working-space of the application to the colorspace of the linearized 
printer / media / driver-settings.
This colormanagement should support both source and destination-profile 
or a devicelink-profile.
Devicelink-profiles deliver more functionality, than traditional 
ICC-based colormanagement with individual profiles for source and 
destination. For CMYK2CMYK, devicelink-profile deliver a better control 
over the black and grey from source to destination.
Devicelink-profiles can also used as an format for very smooth synthetic 
colortransformtions, which often delivers more visual pleasent results 
than not proper made profiles by measurement.
Third point is, that devicelink-profiles are ideal for applying color 
corrections in ICC-workflows. In this case, applications like Cinepaint 
or GIMP are used as profile-Editor.
(I decribed this workflow earlier in this list)

If littleCMS inplemented as part Gutenprint, both possibilties 
(individual profiles and devicelink-profiles) can easly be implemented.

2. color-infrastructure, color settings
---------------------------------------
Looking at colormagement-pioneers like Cinepaint or Scribus, 
colormanagement from working-space to the printer is done inside the 
application.
For the future, this step should be part of the printerdriver.
 From the view of the user, the printer-driver should be able to 
associate driver-settings with linearization files and printer-profiles.
If the user chooses e.g. Epson C64 printer, 720 DpI and Photopaper, the 
printer-drives should choose a predifined linearization-file and a 
profile. The user should also be able to print without this files and to 
setup is own lineariztion-file and ICC-profile for this driver-setting.
The printer-driver should also get the information from the application, 
which RGB- or CMYK-working-space is actually used in the application.

For the user, it is very, very helpful, if he gets in the UI of the 
printerdriver a feedback, if communication between application and 
printerdriver about the RGB- and CMYK-workingspace is really working.

Both in Windows and MacOS X environments, a transparent colormanagement 
from application to printerdriver is often far away from reality and 
causes big troubles during printer-profiling and printing with profiles.

As Scribus and Cinepaint seems to be the applications with best 
implementations of colormanagement yet, it would make sense, if they 
cooperate with the Gutenprint-team on how to implement a communication 
between application and printer-driver about the working-space. Later 
GIMP, Inkscape, CAIRO and other projects can may use the same mechanism.

The mechanism itself should be discussed in the openicc mailinglist. So 
other people can observe, what happens for this applications and Gutenprint.


colorful greetings from berlin
:-) Jan-Peter







--

homann colormanagement ------ fon/fax +49 30 611 075 18
Jan-Peter Homann ------------- mobile +49 171 54 70 358
Kastanienallee 71 ------- http://www.colormanagement.de
10435 Berlin --------- mailto:homann at colormanagement.de