[argyllcms] Re: Any guidelines for creating scanner profiles with Argyll?

  • From: "C" <ml-argyllcms712@xxxxxxxxxx>
  • To: "C." <ml-argyllcms712@xxxxxxxxxx>
  • Date: Tue, 25 Dec 2007 23:35:45 -0800

I'm interpreting your message to mean that you want to profile
the scanner device's response for calibration of the scanner itself.

As far as I know, typically there's no commonly easy way to generate
a sufficiently accurate "print it yourself" test chart suitable for this
purpose.  Certainly one could use targen to create a good RGB test patch
chart with known colors, however your ability to accurately print those
RGB spot colors is only as good as your printer's ability to create
precisely accurate colors.   Certainly a common color calibrated
printer will generate "reasonably" accurate color patches, but still
there's bound to be some inaccuracy and I assume that the magnitude
of those inaccuracies would be greater than the magnitude of error
one might wish to achieve in one's scanner calibration.

Of course if you have an extremely accurate printer that can generate
good spot colors then perhaps it's worthwhile to try to profile a scanner
using an "ad hoc" open-loop printed target.

Read the following and note the reference to an IT8 reference chart
> When no special argument is given scanin is assumed to be scanning an input 
device characterization chart
> (ie. an IT8.7/2 chart), for the purpose of creating a .ti3 data file 
containing the CIE test values and the corresponding
> RGB scanner values. The .ti3 file can then be used for creating an input 
profile using profile.
> The file arguments are: The TIFF file that is to be processed, the image 
recognition template file, the CIE reference
> value definitions for the test chart (sometimes labeled a ".q60" file), and 
an optional name for the image recognition
> diagnostic output. The resulting .ti3 file will have the same base name as 
the input TIFF file.

It is my understanding that one would usually just buy an IT8.7/2 target which 
been printed by a reasonably good printer, but furthermore that printout is then
profiled with an accurate colorimeter so that that specific IT8 chart
(or its identically made production run lot, perhaps) is accompanied by a 
digital data file
of the precise optically determined RGB and/or LAB color values that were
actually printed on that chart.

Then one may calibrate a scanner using that IT8 chart
and its accompanying data file with the ArgyllCMS scanin program as above.

I've seen several sites (which I may only presume to be reputable) commending
the relative value  and quality of the coloraid.de's (by Wolf Faust)
commercially produced IT8 test charts intended  for scanner and possibly camera 
q.v. the comparisons given here for what they're worth:

I have no direct experience or past business relationship with any IT8 chart 
though I'm planning to order a reflective chart probably from coloraid
soon to calibrate my own scanner / camera.

I've seen other pre-manufactured IT8 charts offered for sale indirectly from 
Kodak through
places like Adorama / B&H, et. al.

I've also seen that packages like Profile Prism include a calibrated IT8 chart.

And also that some outfit called LaserSoft apparently sells them too:

Given a sufficiently accurate reflective colorimeter there's no reason
one couldn't use targen print your own IT8 style chart and then validate
its actual profile yourself, though most of the instruments that can do that 
are much more expensive than just buying the certified IT8 target is likely to
be if you have no recurring need for such an instrument for uses other than
scanner calibration.   Though if you did have such an instrument you could
use it to profile a printer (and possibly other devices) or check printed spot 
e.g. to achieve a printer profile that's reportedly better than a common scanner
derived printer profile is likely to be (even if you use a well 
but common sort of scanner).

N.B. that IT8 targets and their production considerations differ depending on 
one is generating a film (transmissive) target or a printed reflective target.

Roger Breton wrote:
I'm not sure which targen options to use since this is a RGB 'device' but
it's not a 'Print' RGB or CMY device. Is it 'Video RGB'? For sure it isn't
Also, when looking at profile options, I fail to find an option to not
create the B2A tables since an input profile only has A2B tables.

Kindest regards,

Roger Breton

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