[argyllcms] Re: Looping back a target

  • From: Bob Coss <bobcoss@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 14 Sep 2011 13:55:53 -0400


I believe you are approaching this incorrectly.  If what you want to do is
get good scans from your scanner, you need to purchase or borrow an IT8 or
equivalent target so you can create the profile for your scanner.  See
http://www.argyllcms.com/doc/Scenarios.html#PS1 for descriptions of the
various targets and their corresponding data files.   I've heard that some
software and hardware come with targets.

It seemed to me that you were creating your own target, and then attempting
to scan in the target.   If you are going to create your own target, you
would need to have a spectrometer that you could use to read your patches to
build the profile.

Once you have a target and the corresponding data file to work with, you
need to follow the instructions for profiling your scanner.  Make sure you
find instructions on how to get the best "raw" scan from the software you
are using.

Usually, the retail scanners like the HP's software use a pretty generic
profile that works reasonably well out of the box.   But to get the best
match from your scanner to your computer, you are going to have to calibrate
your monitor using a hardware device like those listed in the argyll
compatible device list, and profile your scanner.

Later, you might want to get a spectrometer that can be used to create
printer profiles for your printer.    If you don't want to invest in a
spectrometer that can read printer targets, you could always use an online
service or find someone to create printer profiles for you.

Good luck,


On Mon, Sep 12, 2011 at 6:08 PM, Joe Moore <jpvlsmv@xxxxxxxxx> wrote:

> I am new to color management, so please bear with me if I'm asking
> dumb questions.  I have noticed that pictures scanned in from my
> scanner (HP Scanjet 5590) end up with radically different colors when
> displayed on screen, than they do on paper.  I assume that I can
> characterize the scanner, then use that information to remap the
> scanned images into something that looks right on screen.  I'm not
> looking for something incredibly precise, just to have flesh-toned
> skin.  The Autocorrect settings in the scanner software, well, don't.
> I've created a test target with targen and printtarg to a TIFF file.
> But before I took this into the physical world, I wanted to see how
> the rest of the image processing would go.  My overall plan is to take
> the target down to my local photo print place and get something that's
> "close enough" to what's on the screen that I'm satisfied.
> targen -v -d 2 target4
> printtarg -i SS -v -a .4 -t 300 -p 4x6 -s -m 10 target4
> scanin -dipn -v1 target4.tif target4.cht target4.ti2 diag.tif
> The target I've created (through the various steps) can be found at
> http://content.iegrec.org/target4.zip
> When I feed the target.tif back into colprof, however (which I think
> should create a null ICC profile, i.e. one that makes no changes to
> the color space, however looking at the curves in the ICC Profile
> Inspector, they are not flat at all.
> Looking at the TI3 file, the deviations are very small (<10^-13).  But
> colprof -v has a very interesting idea of what "White" is in this
> case:
> target4>colprof -v target4
> No of test patches = 836
> Estimating white point
> Picked white patch 283 with XYZ = 0.907340 0.982510 0.858160, Lab =
> 99.319739 -7.096156 -3.825529
> Picked black patch 5 with XYZ = 0.010000 0.010000 0.010000, Lab =
> 8.991442 1.317040 -2.855386
> Approximate White point XYZ = 0.907340 0.982510 0.858160, Lab =
> 99.319739 -7.096156 -3.825529
> As you can see from the RGB values it picked, it is nowhere near a
> pure color (the choice of black is a lot closer to black).  Guessing
> from the lines in target4.TI3, it's looking at patch V06 which is RGB
> FFFFe1 not FFFFFF.
> Am I missing something in this process?  Is it a futile quest to try
> to get a 1:1 ICC profile out?  Why is colprof not going with the true
> white patch at R10, R11, Q19, or R12?
> Thanks,
> --Joe

Hay que aprender algo nuevo todos los días

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