[Openicc] Colormanagement in Gutenprint

[Jan-Peter Homann]

Hello List

I will try to describe, how may colormanagement could be implemented in 
Gutenprint without a lot of steps to do.

The goals of the concept:
- Open for high-end user, which do individual profiling
- Use of cannend profiles for standard-usage
- Use of logical printers as standard printing UI
- Easy creation of special installation packages with standard-sets of 
logical printers

Later the concept also describes the process of setting up a 
colormanagement-workflow from the application to the printer.

But first, what should be done in Gutenprint ?

1. Integration of littleCMS into Gutenprint
--------------------------------------------
- The input of Gutenprint is always a  RGB or CMYK Rasterimage with 8 or 
16 Bit color depth.
- The user can specify source-profile, printer-profile, 
rendering-intent, blackpoint-compensation-flag
(or as alternative a devicelink-profile, which converts directly from 
source to destination)

2. Inkliniting and linearization
--------------------------------
Making a good linearization, as basis for good ICC-transformtions needs 
to steps:
2a. individual linearization of the pure CMYK channels
2b. Inklimiting for a maximum amount of color (GCR)

The user should be first able to print a testchart for making 2a. 
"individual linearization". If this is done, he prints a testchart using 
the individual linearization curves for step 2b.   "Inklimit/GCR"
In the last step he prints the testchart for profiling with active GCR 
and active individual inklinearization.

3. Colorworkflow in Gutenprint
-------------------------------
After the calculation of the printer-profile, the colorworkflow in 
Gutenprint is as follow:

Image to print

source profile
destination profile
Inklimit with GCR
individual channel-linearization

printout



3. Configuring logical printers
--------------------------------
A logigal printer consists of:

- settings for littleCMS
- GCR and individual Ink-linearization files
- printer-specific-settings (resolution, dithering, mediatype...)
- name of setting (source-profile, printer, mediatype, resolution)
(e.g. AdobeRGB_Eps2100_photpap_720)

4. Export and Import for logical printers
-------------------------------------------
If somebody is making linearization-curves, profiles and a logical 
printer, he should be able to export this to one package wich contains 
all files. Such files could be imported from other users, and they can 
instantly use the logical printer without any need for special 
configurations.

Who makes the profiles ?
-------------
There are several people available, which would do the work of profiling 
and building logical printers. First there are the opensource minded 
people, which just say, if I made profiles for my printer/media setting, 
I want to share it with other people.
But the biggest source would be resellers of media and ink-sets. If they 
deliver profiles and a logical printer, they make it easy for their 
customers to use their media.

The user perspective
--------------------
So  e.G. Carol is making photo-retouche with the new GIMP 2.5, which 
supports AdobeRGB as working-space and she also has a monitor-profile 
for her monitor.

She has an Epson 2100 and uses Epson Photopaper
She goes to the Gutenprint homepage an finds a download for a logical 
printer-package with all profiles.

After the download, she just pushes the installer, is happy when she 
find the name of the logical printer in her printing dialogue and likes 
the results, which are coming ou now.

But what about the prints of her webdesign ?

Carol learned, that webdesign should be done in sRGB. So, she has 
converted  the high-res AdobeRGB photos to lowRes sRGB jpgs.

She also learned, that the logical printer is always made for one 
special working-space. But no matter, she opens the 
"Gutenprint-configuration-assistant", which allows her to duplicate an 
existing logical printer and change only the RGB-workingspace.
She saves the new logical printer with the name 
"sRGB_Eps2100_photopap_720" and has now two logical printers in her 
printing dialogue.
One for her photo-retouching in AdobeRGB and one for her webwork in sRGB.

Printing in a network environment
---------------------------------
The concept of the logical printer makes it easy to use a server with 
GhostScript / Gutenprint in a network.

Imagine a system administrator in a design agency. He is not able to 
make his own profiles, but he can ask the graphic designers what 
working-spaces they are using. He gots the answer
- AdobeRGB for photos
- sRGB for web
- SWOP for printing
As he is familiar with CUPS, GhostScript and The Gutenprint-Installer, 
he sets up following virtual CUPS-printer in the network:

sRGB-standardpaper
SWOP-standardpaper
AdobeRGB-photopaper
SWOP-photopaper

 From the view of the designers, these are normal printers. Internally, 
the printing-data from the designers are ripped with GhostScript to 
hiRes Bitmaps without colormanagement. According the installation, the 
HiRes Bitmaps from different virtual CUPS/GhostScript-Printers are 
colormanaged  with different logical-printers, which the administrator 
downloaded from the Gutenprint-side.

The Graphic-Designers are happy with the print-results, but the virtual 
printer "SWOP-photopaper" should deliver real proofing-quality.
So, the systemadministrator calls a colormanagement-specialist, which is 
doing an individual linearization and profiling for printing on 
photopaper with the already installed logical printers
- AdobeRGB-photopaper
- SWOP-photopaper

Now the design-agency can make their own digital proofs.
---

After reading the mails on this list, it should possible, to build such 
workflows without big changes in the architecture of actual design 
applications, CUPS, GhostScript and Gutenprint.


Greetings
:-) 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