[argyllcms] Re: Difficulty profiling new iMac

  • From: Andreas Baitis <abaitis@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 14 Sep 2007 15:35:06 +1000

This may or may not account for your lack of success with your Apple. If there 
is any truth in the Macbook complaint, maybe Apple have done the same with 
the Imac???

See here:

http://blogs.business2.com/apple/2007/05/behind_the_appl.html

http://www.apple.com/imac/specs.html



On Friday 14 September 2007 14:46, Ben Goren wrote:
> I  sent   this  about   45  minutes  ago   and  it   still  hasn't
> appeared. Here it is  again, but without the  attachments; you can
> find them at:
>
>      http://trumpetpower.com/pub/argyll/
>
> So, late last  week I broke the  piggy bank to get  myself a shiny
> new  24" iMac. I'm  quite happy  with  the computer,  but I'll  be
> damned if I can't seem to make a decent profile for the display!
>
> First,  a bit  of  explanation. I've tried  all  sorts of  things,
> including  tweaking  every knob  I'm  aware  of in  Argyll,  using
> different test images, different  (ICC-aware) applications to view
> the  test  images, etc. What  follows  is  simply an  illustrative
> sample.
>
> For  the easiest-to-use  test image  to illustrate  my troubles  I
> created in Photoshop  a Lab file the same pixel  dimensions as the
> display and used  the gradient tool to fill from  L=0, a=0, b=0 to
> L=100, a=100,  b=100. (I get the  same results in  RGB, grayscale,
> etc., and the  problems are visible in everything  from other test
> images to movies in VLC.)
>
> No matter  what I do,  the dark shadows,  from about L=2  to L=16,
> have  a greenish,  maybe slightly  blue, cast  to them. (Sometimes
> they're  yellowish instead  of  bluish.) The worst  is usually  at
> about L=6. The exact area and peak have varied with the particular
> profile.
>
> However, if I select a color  space profile -- such as AdobeRGB or
> sRGB -- in the Displays Preferences,  the entire gray ramp is very
> neutral and even.
>
> Here's the most recent attempt, complete with files:
>
> First, I check the native response of the display with dispcal. It
> tells me:
>
> $ dispcal -v -y l -R
>
> [. . .]
>
> Uncalibrated response:
> Black level = 0.35 cd/m^2
> White level = 266.20 cd/m^2
> Aprox. gamma = 2.19
> Contrast ratio = 759:1
> White chromaticity coordinates 0.3128, 0.3281
> White    Correlated Color Temperature = 6507K, DE to locus =  3.9
> White Correlated Daylight Temperature = 6507K, DE to locus =  0.8
> White        Visual Color Temperature = 6367K, DE to locus =  3.8
> White     Visual Daylight Temperature = 6535K, DE to locus =  0.8
> The instrument can be removed from the screen.
>
> That's close  enough to  gamma =  2.2 and  temperature =  D65 that
> that's what I'll use for everything from here on out.
>
> Next, I use dispcal to create the .cal file:
>
> $ dispcal -v -y l -g 2.2 -e -H iMac\ 2007-09-13
>
> [. . .]
>
> Commencing device calibration
> patch 6 of 6
> Black = XYZ   0.41   0.39   0.74
> Red   = XYZ 119.42  63.48   3.16
> Green = XYZ  87.68 179.75  24.81
> Blue  = XYZ  49.90  25.60 268.25
> White = XYZ 255.43 267.28 293.63
> patch 64 of 64
> Initial native brightness target = 267.277738 cd/m^2
> Target white value is XYZ 255.431672 267.277738 293.627647
> Target black point = 0.415598 0.392467 0.713159
> Current gamma curve offset = 0.068389, Gamma curve power = 2.432115
> Total Iteration 3, Final Samples = 64 Final Repeat threshold = 0.800000
> Creating initial calibration curves...
> Doing iteration 1 with 16 sample points and repeat threshold of
> 3.200000 DE
> patch 16 of 16
> Brightness error = 0.000000 cd/m^2
> White point error = 0.000000 deltaE
> Maximum neutral error (@ 0.157165) = 1.594979 deltaE
> Average neutral error = 0.687945 deltaE
> Computing update to calibration curves...
> Doing iteration 2 with 32 sample points and repeat threshold of
> 1.600000 DE
> patch 32 of 32
> Brightness error = 0.000000 cd/m^2
> White point error = 0.000000 deltaE
> Maximum neutral error (@ 0.077741) = 0.915395 deltaE
> Average neutral error = 0.305202 deltaE
> Computing update to calibration curves...
> Doing iteration 3 with 64 sample points and repeat threshold of
> 0.800000 DE
> patch 64 of 64
> Brightness error = 0.000000 cd/m^2
> White point error = 0.000000 deltaE
> Maximum neutral error (@ 0.007987) = 0.758240 deltaE
> Average neutral error = 0.249896 deltaE
> Computing update to calibration curves...
> Doing verify pass with 100 sample points
> patch 100 of 100
> Verification results:
> Brightness error = 0.000000 cd/m^2
> White point error = 0.000000 deltaE
> Maximum neutral error (@ 0.000000) = 1.585869 deltaE
> Average neutral error = 0.341614 deltaE
> The instrument can be removed from the screen.
>
> Here's the .cal file:
>
>
> Next, I  create a  small test  chart to  use to  pre-condition the
> ``real'' one later:
>
> $ targen -v -d 3 -f 50 iMac\ 2007-09-13\ small
>
> Then, I read it:
>
> $ dispread -v -y l -k iMac\ 2007-09-13.cal -s -H iMac\ 2007-09-13\ small
>
> The .ti3 file:
>
>
> And, of course, create the profile:
>
> $ profile -v -A Apple -M iMac -D "iMac 2007-09-13 small" -C
> "Copyright (c) 2007 by Ben Goren" -i D65 -o Shaw iMac\ 2007-09-13\ small
> No of test patches = 50
> Estimating white point
> Approximate White point XYZ = 2.416478 2.608524 2.769155, Lab =
> 143.682114 -9.120046 -24.150496
> Creating optimised per channel curves
> About to optimise temporary matrix
> ...................
> About to optimise input curves and matrix
> ...................
> About to optimise output curves and matrix........................
> About to optimise input curves and matrix again.
> About to optimise input, matrix and output together...............
> About to adjust a and b output curves for white point
> Creating fast inverse input lookups
> Compensate scattered data for input curves
> Compensate scattered data for output curve
> Create clut from scattered data
> ******************************************************************
> Find white & black points
> White point XYZ = 2.431605 2.622663 2.770560, Lab = 143.970110
> -8.947177 -23.704592
> Black point XYZ = 0.004504 0.004745 0.007474, Lab = 4.286515
> -0.288699 -6.717227
> Fixup clut for white point
> Check White point XYZ = 2.431605 2.622664 2.770560, Lab = 143.970113
> -8.947177 -23.704592
> Done A to B table creation
> Creating B to A tables100%
> Done B to A tables
> profile check complete, peak err = 4.885327, avg err = 1.800126
> Exectution time = 11.130000 seconds
>
> Here's that profile:
>
>
> I then feed that to targen for the ``real'' profile:
>
> $ targen -v -d 3 -f 1000 -c iMac\ 2007-09-13\ small.icc iMac\ 2007-09-13
>
> Here's the resulting .ti1 file:
>
>
> Reading the chart:
>
> $ dispread -v -y l -k iMac\ 2007-09-13.cal -s -H iMac\ 2007-09-13
>
> Creates this .ti3 file:
>
>
> Now,  at this  point...it really  doesn't matter  what I  do. If I
> create a shaper profile:
>
> $ profile -v -A Apple -M iMac -D "iMac 2007-09-13" -C "Copyright (c)
> 2007 by Ben Goren" -a s -i D65 -o Shaw iMac\ 2007-09-13
>
> then  ``pure''  black  is  really   a  dark  green,  and  all  the
> single-digit LAB values show a green to yellow color cast.
>
> A LUT profile doesn't show as  much of a color cast, but ``black''
> still is  noticeably lighter than  it should be, there's  not much
> variation  up to  about  L=5 --  at which  point  there's a  sharp
> transition to a lighter yellowish-greenish cast that gets yellower
> up to about L=15, when it becomes more neutral up to about L=20.
>
> The worst  part about this  is that, the more  I do, the  worse it
> gets.  This latest LUT profile is  actually one of the better ones
> of the lot.  A tens-of-thousands of patches profile I did (letting
> it  run overnight)  was  unusable, and  adding  in thousands  more
> neutral  patches  (in device  space,  reading  them, and  manually
> adding them  back into  the original .ti3  file) only  made slight
> improvements. If I use -q u,  it's a bit smoother (there's banding
> in  all  the  profiles,  including  the  color  spaces  ones  like
> sRGB), and  the exact location  and hue  of the color  casts might
> change...but nothing  has made it  go away. A shaper  profile from
> 4000 patches  I did  this afternoon  is so far  off it's  not even
> funny,  and the  LUT version  was worse  than this  1000-patch one
> here. I've even  used displin from  the start instead  of dispcal,
> again with no luck.
>
> Help!
>
> Cheers,
>
> b&

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