[Openicc] Open Source compatible AdobeRGB profile

[almccart at lexmark.com]

Hi All,

There seems to be some confusion regarding the relationship between ICC 
profiles and
the color encoding in an image or document file. 

The basic rule is - when any digital color object is created it must be 
labeled by the creating
device or by a person who knows the characteristics of the creating 
process.  The label must indicate
the current actual color space, i.e., color space encoding = white point, 
primaries, gamma, digital 
encoding rule, etc.  This can be thought of as the "source" encoding. Such 
source color encoding definition
information should be created by scanners, cameras, and authoring 
applications.

The label must match the actual encoding, e.g., an Adobe RGB label can be 
linked to an image
encoded in Adobe RGB. No other label can be associated with that image. 
RGB color spaces
may sound similar - but in fact the well known RGB color spaces [color 
encodings] are quite
distinct from each other.  The same is true for the various different CMYK 
color space encodings.

A color space encoding label may be a tag that gives the name of a 
standard color space, such as
sRGB or Adobe RGB, or the label can be an ICC profile.  An ICC profile can 
provide an unambiguous
definition of any color space, whether it is standard or proprietary.

If the label is a tag that gives the name of a standard color space, then 
a profile for that color space
optionally does not need to be carried with the content - it can be 
retrieved and applied whenever the content is used.
Alternatively, both a color space name tag and a profile can be attached. 
Again in this case both must 
match exactly to the actual contents of the color space encoding.

A color management color conversion operation requires both a source 
profile [the current encoding] and
a destination profile [ the next encoding representation - typically for a 
display or print device].

Any system that handles color documents or images needs functionality to:
a. Honor profiles that come attached to content [image, document] files. 
These profiles answer the
question - What are the current color encodings in the file?
Complex documents can contain multiple source profiles - each linked to a 
different content object.
Note: an output profile may be included in certain PDF/X files  - that 
profile indicates the intended output 
color encoding and is used as the destination profile in a color 
management conversion operation. 
b. Provide for retrieval of standard profiles [actual std and defacto std] 
to be used when content files
use the color space label approach. [e.g., profiles provided through links 
on the ICC website: www.color.org]
c. Define an RGB 'default' interpretation policy [i.e., default source 
label]  to be used when no real label is present. 
Note that color management results will only be correct when the guess is 
correct. There are many legacy
files incorrectly labeled as 'deviceRGB' that have to be handled.
d. Define a CMYK 'default' interpretation policy [i.e., default source 
label] to be used when no real label is present.
Note that color management results will only be correct when the guess is 
correct. There are many legacy
files incorrectly labeled as 'deviceCMYK' that have to be handled.
e. Never drop - always carry through - color space encoding labels of all 
kinds. Note - a profile that is
carried with an image file or content file must always take precedence 
over a "standard" profile of the same
name.  The embedded profile might have been edited for the particular use. 

f. Provide for selection/retrieval of a destination profile for a color 
management color conversion operation - this
can be an RGB profile or a CMYK profile, etc.
f. With Version 4 profiles, use the Version 4 profile - profile ID field - 
to check whether two profiles are the same.

Specifics for each of these requirements vary depending on image and 
document formats and color management tools.

My apologies if this is review for most of you.  It seemed from some 
comments that a background 
statement might be helpful.

Best regards,
Ann McCarthy
Lexmark CPD
Imaging Systems Engineering

"To every complex problem there is a simple solution - and inevitably it 
is wrong"   HL Mencken




Sven Neumann <sven at gimp.org>
Sent by: openicc-bounces at lists.freedesktop.org
07/05/2006 04:31 PM

 
        To:     Hubert Figuiere <hfiguiere at teaser.fr>
        cc:     OpenICC Liste <openicc at lists.freedesktop.org>
        Subject:        Re: [Openicc] Open Source compatible AdobeRGB profile


Hi,

On Wed, 2006-07-05 at 16:29 -0400, Hubert Figuiere wrote:
 
> > What about http://www.eci.org/eci/en/040_colour_standards.php ? Their
> > profiles could serve as an alternative for AdobeRGB, couldn't they?
> 
> How does it help if the pictures are in the AdobeRGB colorspace?

Users would still have to download the AdobeRGB profile from Adobe, of
course. But at least they would have a reasonable RGB profile to work
with. And long-term it might make AdobeRGB less important.


Sven


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