[Openicc] meta data in test chart

[Alastair M. Robinson]

Hi,

On 25/01/11 22:18, edmund ronald wrote:

> Look guys, somehow we need to cobble up a workflow that works, and
> that even works with profiles generated by standard tools.
> Suggest something! Or else we'll have to go to all-sRGB and
> all-AdobeRGB for consumers.

OK how about this:

Applications send data in one of four classes:
* Postscript or some other legacy format.
* PDF with untagged image data
* PDF with ICC-profile-tagged images
* PDF with images tagged as DeviceCMYK or DeviceRGB, depending on which
colourspace the driver's operating in.

The last two variants are easy to handle: tagged images should be
converted to the printer's profile, while DeviceXXX images should be
passed through unmolested (provided they match the driver's colourspace
- if not the job needs to fail; silently converting would make
diagnosing problems much harder.)

For legacy Postscript and Untagged PDF I think we need an option
provided by the print subsystem, be it CUPS, the PPDs, the CPD or whatever:
"Default Colour Interpretation: [sRGB  |  AdobeRGB  |  Device Native]"
This describes the colourspace in which input data is assumed to be.  By
default it would be set to sRGB, so J. Random User will get the expected
results (provided a profile is available for his print settings) if he
just prints a photo without setting anything up, but the queue can be
set unambiguously to Device Native for profiling purposes.
If there's no profile available, the printer's profile will be assumed
to be sRGB - thus with the default colour interpretation of sRGB the
conversion will be a no-op and you'll effectively get native device
response until a profile exists.
The fly in the ointment is what to do about PDFs with icc-profile tagged
images when the queue's in Native mode.  Personally I'd be in favour of
rejecting such jobs outright than trying to do anything "clever".  An
outright failure to print is much easier to diagnose than corrupted
profiling test charts caused by a rogue conversion.

What problems can people see with this?

All the best
--
Alastair M. Robinson