[Tfug] Color Management

[Bexley Hall]

Hi Zack,

> > Likewise, I imagine monitors and printers can only be profiled
> > with some external hardware (though I could envision being able
> > to profile a printer with a suitable "source" and a *profiled*
> > scanner?)
> 
> There are some cheap monitor calibration devices ($100-300)
> that will generate a profile. Not sure on the free software
> compatibility of them.

Free isn't an issue as much as how they work and how WELL
they work
 
> Often, printers will ship with profiles for a specific ink/paper

Yes, I have dozens of profiles for some of my printers.  Usually,
it is *literally* a manufacturer specific paper/ink combination.
I.e., not just "high gloss inkjet paper" but, rather, "high
gloss inkjet paper manufactured by XYZ corporation produced in
paper mill #235-B by Joe Tiglione on May 14th *before* lunch..."

:-/

Unfortunately, without an understanding of what is actually
involved in the technical process, its hard to decide (a priori)
whether there is any *real* difference between this paper and
"some stuff I found lying on the floor in the closet"  :-/

E.g., tell me the frequency response of these speakers is flat
to +/- 1 dB and I *know* I'll never hear the difference...

> combination, and in my experience, these are specific to
> photoshop.

Not sure why that should be.  I thought the profiles were
application independant (or, is photoshop the only application
that fully *implements* this?  e.g., does the application
massage the data as it is being printed/displayed?  or, is
that offloaded to the associated driver??)

> You can buy a calibrator to generate a printer profile, but
> these tend to be much more expensive (>$1000)

Hence the suggestion of using a calibrated scanner to
calibrate a printer.  I.e., if I scan a known target,
I now know how to compensate my scanned images to reflect
"reality".  So, if I *print* a known *source* and then
scan *that*, I can figure out how "wrong" my printer is.

Or, is the process so imperfect that the errors add up
REALLY FAST?
 
> > Lastly, can profiles be "convolved"?  E.g., if you scan something
> > on an unprofiled scanner, can you later convolve P(scanner) with
> > P(printer) at print time (i.e., redefine P(printer) as such)
> > to get the same result as if the image had been scanned on the
> > *profiled* scanner?
> 
> The end to end process requires calibration all along the,
> and devices
> capable of reproduction of the same colorspace as the
> original.

But, I don't see how that *should* be the case.  I.e., I would
imagine that each "profile" is just a "transform" of sorts that
maps an input image into an output image.  So, you should be able
to create a *composite* profile that goes through N steps.

E.g., you should be able to compare (visually with an appropriate
colorimeter) an image on your screen with a printed image and
develop a profile for "screen to printer" without dealing with
any of the intermediate steps (assuming you use the same
application, etc)

> > Are there any secret gotchas that differentiate
> printer profiles
> > from, e.g., monitor profiles?  (in how the color is
> conveyed to
> > the beholder)
> 
> Depends on the format used.  Printer and Monitor
> calibration profiles
> will be different just by the nature of the device,
> monitors being RGB
> and printers CMYK (sometimes plus a few).  ICC is a
> standard, but it tends to be irregularly implemented.

(sigh)  Thanks.  I guess I'll have to dig through some sources
and see what I can find about the profiles themselves.

--don