[Openicc] color-policy vs. color-infrastructure

[Jan-Peter Homann]

Some comments below

:-) Jan-Peter

Graeme Gill schrieb:
> Jan-Peter Homann wrote:
> 
>> 1) CMYK-Output with individual black generation
>> -----------------------------------------------
>> Reading the colorsync-mailinglist, prepress users often want to change 
>> the black generation of the standard CMYK-profiles from the Adobe 
>> Creative Suite. To do this, they need to buy a profiling software, 
>> which coasts at least 1000,- $
>> In argyllcms, this is just a function to use. (Please correct me 
>> graeme, if I´m wrong). So for e.g. the GIMP, Scribus, Cinepaint or 
>> later Inkscape, it would be not a big deal to deliver this functionality.
> 
> 
> It's certainly possible to do this, but I'm not sure if it fits
> in the core of a CMM. It's of interest only to graphics professionals
> who are likely to want to re-target CMYK, while typical users (even
> creative types) are far more likely to be working in more flexible
> RGB or CIE spaces, and leave the conversion to the more device and
> function specific CMYK until the end of the process (assuming the
> goal is printed output).


Even the creative people, which are working mostly in RGB needing often 
CMYK-profiles with different black generation.

For RGB-images/photos with mainly neutral colors, it is common to use an 
profile with heavy GCR for separation to CMYK.
For RGB-images/graphics with black = RGB 0/0/0 or gray R=G=B it is 
common to use an profile with maximum GCR for sepration.
This is espcialy useful for separation of screenshots or 
SVG-vectorgraphics.

If you are not using a profile with maxGCR black generation for this 
task, RGB-black and and RGB-gray is separated to all four CMYK-plates 
and not only to the black plate.

So, control over black generation is very important for ALL users, which 
are working in RGB and need control for the conversion to CMYK.

So an universal modul for calculating CMYK-profiles with different black 
generation from a given profile or standard characterization-data would 
be helpful for all LINUX graphics arts applications (GIMP, Scribus, 
Inkscape, ImageMagick....)

For this, argyllcms is delivering the necessary functionality.

>> 2) Storing color corrections as abstract or devicelink-profile
>> ------------------------------------------------
> 
> 
> This is another good idea supported by the ICC format and very
> under-utilized.
> 
>> graeme, can you describe, if this is already possible with argyllcms, 
>> or  how much work must be invested, to do this ?
> 
> 
> It's not too hard with the building blocks there. Convert the before and
> after RGB values into PCS (probably L*a*b*). If the image is not
> a test chart (ie. it was a real image), reduce the number of color
> mapping points using a quantisation algorithm (median cut worked well
> for me in xli). If the mapping points don't form a full regular grid,
> throw them into the thin plate spline code and create a regular grid
> mapping. Save the regular grid as an abstract profile.


With devicelink-profiles, there is a second universal way to store 
colorcorrections and apply them via filter to several kinds of data.

just manipulate an an RGB- or CMYK-image which represents a testchart, 
and convert the manipulated image back to an CGATS textfile.
Then link direct the original RGB- or CMYK values directly to to the 
manipulates ones.
In this case, you don´t need a PCS or any intent. It is just a way to 
store color corrections into a devicelink-profile.

So every application, which have tools for color correction could have a 
button "save correction as devicelink-profile"
Every application which has an menu for filtes ao images or 
vectorgraphics can use the filter "apply color colorrection from 
devicelink-profile"

graeme,
can you explain, if argyllcms offers following possibilities:
- convert a CGATS style textfile (describing only a testchart, no 
Lab-values) to an image, where every CGATS text entry is represented by 
only one pixel ?
- convert every RGB- or CMYK-value of an imagepixel to an CGATS style 
textdocument
- link to two CGATS style textfiles with the same number of color 
entries to an devicelink-profile ?

If yes, argyllcms would be an excellent tool for other programmers to 
store color corrections as devicelink-profile.


:-) Jan-Peter



> 
> Graeme Gill.
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> 


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