[argyllcms] Re: Wrong gamma / color rendition worse than before calibration
- From: "Thomas Bartosik" <tbartdev@xxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 07 Sep 2011 20:18:22 +0200
Well, that's bad news.
Though I cannot agree on the viewing angle sensitivity (I can barely see any
color shifting, even at close to 180°...) I think you're the one to know this
better...
My only question is this:
Is the screen only subjectively better without calibration or is the reduced
gamut a problem for argyll and the result is therefore bad?
I mean before calibrating and profiling I could at least differentiate more
color nuances than afterwards. This is somewhat strange. What IS better after
calibrating and profiling?
Even the worst display I have ever seen (also in a notebook, viewing angle of
maybe 60°, and the white level problems mentioned in my first post) got A LOT
better by calibrating it.
Or is seeing more brightness steps no improvement? I don't know, maybe it's too
subjective.
In an uncalibrated state, I get output from my printing company that's pretty
close to what I design. After calibration I am sure the output will differ a
lot more. I am questioning whether there are situations where not calibrating
might be better. Or is this a limitation in argyll?
I understand my display may not be as good as I thought it to be ;-( but
shouldn't calibrating at least improve it a little and not make it worse?
I have uploaded a HQ pass done in dispcalGUI (just tried it out: The graphs are
pretty neat!) to
http://rockbrew.com/argyll
What still makes me wonder is that no other LG panel in a thinkpad has that
strange strong low end bending of the gradation curves. They are all different
but more similar to one another that to mine.
I somewhere read the green gel used in the spyder2 display filter might give
wrong measurements over time. Can I completely rule out errors in my
colorimeter?
Thank you for your time and explanations!
Florian Höch wrote:
> Hi,
>
> if the profiles are any indication, then the color gamut of that screen
> is (a lot) smaller than sRGB (not uncommon for TN panels, especially in
> Laptops/Notebooks), leading to clipping.
> Same for black. Many Laptop/Notebook displays have a pretty poor black
> level (some monitor profilers cheat by scaling the black of the profile
> to absolute zero. Argyll does not do this).
> I wouldn't pay too much attention to those gamma test images, as TN
> panels are very viewing angle sensitive, and combined with the usually
> pretty 'bendy' calibration curves needed to make such a display behave,
> there isn't much useful information to discern from those images.
> In summary, I'm afraid your problems are not fixable via different
> calibration/profiling settings, as they seem like hardware limitations
> of the screen.
>
> Am 07.09.2011 13:18, schrieb Thomas Bartosik:
> > Hi list!
> >
> > I am somehow at a loss as to how to solve my gamma problems..
> >
> > 1) What I want to do:
> > Have a calibrated display for a) web work and primarily b) print work
> sent to a printing studio. They accept ISO coated CMYK PDFs.
> >
> > 2) What I have done:
> > I got a spyder2 for cheap, i know it's not the best, but I'd like you to
> comment on the issue and tell me whether the colorimeter's quality might
> be the problem.
> >
> > I used the colorimeter to calibrate/profile really bad and cheap
> displays (e.g. one notebook display that did not differentiate between
> 235,235,253
> white till 255,255,255 white, everything was white)
> > The calibrated/profiled results of these displays are very pleasing and
> now show nuances that were completely unseen before.
> >
> > Now my problem is my own display in a Thinkpad T61p. This is (an
> expensive) LG 1920x1200 display that has really good reviews in most articles
> I
> have read so far. In an uncalibrated/unprofiled state, colors look really
> good but a bit bluish and the brightness distibution is also very good
> (subjectively, to my eyes). i.e. I can differentiate 252,252,252 white from
> full
> white and also 3,3,3 black from full black. This has not been the case with
> nearly all other uncalibrated/unprofiled displays I have seen so far.
> >
> > I did several dispcal runs, and they more or less ended up in the same
> color rendition.
> > (I tried with -t 6504 and -gs and without both)
> >
> > Now the problem I face is this:
> > All dark nuances in pictures are too dark. And I think I can really say
> that in an absolute manner, it's not only a subjective thing.
> > The same goes for bright tones.
> >
> > If I look at
> > http://www.visibone.com/color/chart_847.gif
> > in a color managed app like gqview or gimp with the .icc profile loaded
> and applied, I cannot differentiate between FF66FF, FF33FF and FF00FF while
> I can do so unmanaged or with just dispwin loading the profile and the app
> not loading it. As far as I have read till now this huge difference
> between using a color managed desktop (i.e. loading the profile with dispwin
> or
> xcalib) and then applying the same profile again with a color managed app
> should not be that dramatic.
> > I suspect something's wrong with the measurements taken or the profile
> created.
> > Can anyone give advice as to in which direction I should look to solve
> this problem?
> >
> > As an interesting sidenote, I found a profile for a similar display ( A
> T61 LG panel, resolution could be different, I don't know more about this
> profile), and apart from its D50 whitepoint the effect of not seeing
> different magenta nuances is quite the same (at least FF66FF and FF33FF are
> indistiguishable). This profile was taken with a gretag macbeth device, I
> guess
> on windows.
> > I found an additional profile that's also for an LG in a Thinkpad, with
> the same effect on magenta.
> > This makes me believe my profiling data and measurement values seem to
> be probable at least. But why don't I see those magenta nuances?(the same is
> also valid for some green and blue areas...)
> >
> > All of the profiles and my cal and icc file are at
> > http://rockbrew.com/argyll
> > (The T61p-full-brightness... is mine)
> >
> > Do you see differences in these colors?
> > If I do the monitor test on
> > http://www.lagom.nl/lcd-test/
> > after having applied a profile, I can barely make out the lowest stripes
> in the contrast test. The gamma test seems more accurate than without
> being calibrated, but the area of blending in is a bit broader. The bars all
> blend it at around 2.2 which I never managed to do with just the nvidia
> controls, but the blue gamma is somewhere around 2.6, which puzzles me.
> > NB: This is when I test it in opera, i.e. the .icc profile is loaded by
> dispwin but not the browser!
> > If I download the contrast and gamma .png and look at them at zoom 1:1
> in gqview with the profile loaded, I get these gamma readings:
> > 48% | 25% | 10%
> > R G B W | G W | G W
> > 2.3 1.6 2.8 2.3 | 2.2 2.3 | 2.2 2.3
> >
> > The 1.6 at green is pretty extreme, and the 2.8 at blue as well (tho I
> cannot really say it is 2.8 for sure as 2.5 till 3.0 is nearly the same
> level to my eye)
> >
> > Without any calibration, the gamma and contrast test are perfectly OK,
> but could be a bit better (this is what I wanted the calibration/profiling
> to do for me!)
> >
> > If I tune the values in nvidia-settings for the lagom lcd test and dump
> the values with dispwin -s I get nvidia.cal (also at the webspace above).
> This is the (subjectively) best setting I have till now...
> >
> > Maybe I have to give different -g or even -G values? I do not understand
> -G at all and I think -g should best be set to the display's native gamma
> as it will result in the least banding artifacts and does not really matter
> as the color managed app should compensate for it anyway...
> >
> >
> >
> > I hope there's some advice you can give as I am somewhat clueless..
> >
> > Thanks in advance!
> >
> > th
> >
> > Here's a rundown of the calibration I've done.
> >
> > blackknight ~ # dispcal -yl -v -R
> > XRandR 1.2 is faulty - falling back to older extensions
> > Setting up the instrument
> > Instrument Type: ColorVision Spyder2
> > Serial Number: 00633553
> > Hardware version: 0x0307
> > Place instrument on test window.
> > Hit Esc or Q to give up, any other key to continue:
> > patch 3 of 3
> > Measuring VideoLUT table entry precision.
> > patch 6 of 6
> > patch 6 of 6
> > patch 9 of 9
> > patch 9 of 9
> > Uncalibrated response:
> > Black level = 0.40 cd/m^2
> > White level = 119.19 cd/m^2
> > Aprox. gamma = 2.29
> > Contrast ratio = 300:1
> > White chromaticity coordinates 0.3269, 0.3578
> > White Correlated Color Temperature = 5726K, DE 2K to locus = 12.5
> > White Correlated Daylight Temperature = 5726K, DE 2K to locus = 9.6
> > White Visual Color Temperature = 5366K, DE 2K to locus = 12.2
> > White Visual Daylight Temperature = 5475K, DE 2K to locus = 9.3
> > Effective LUT entry depth seems to be 10 bits
> > The instrument can be removed from the screen.
> >
> >
> > blackknight ~ # dispcal -m -yl -t 6504 -gs -v -O "Thinkpad T61p
> 1920x1200 LG full brightness Argyll-1.3.1 sRGB D65 Spyder2" -o
> /usr/share/color/icc/T61p-full-brightness-argyll-1.3.1-sRGB-D65XRandR 1.2 is
> faulty - falling
> back to older extensions
> > Setting up the instrument
> > Instrument Type: ColorVision Spyder2
> > Serial Number: 00633553
> > Hardware version: 0x0307
> > Place instrument on test window.
> > Hit Esc or Q to give up, any other key to continue:
> > Display type is LCD
> > Target white = 6504.000000 degrees kelvin Daylight spectrum
> > Target white brightness = native brightness
> > Target black brightness = native brightness
> > Target gamma = sRGB curve
> > Commencing device calibration
> > patch 6 of 6
> > Black = XYZ 0.35 0.35 0.40
> > Red = XYZ 44.06 26.35 3.27
> > Green = XYZ 33.71 59.85 10.98
> > Blue = XYZ 17.84 17.99 78.99
> > White = XYZ 95.06 103.78 92.64
> > patch 128 of 128
> > Initial native brightness target = 103.784294 cd/m^2
> > Had to scale brightness from 103.784294 to 81.568913 to fit within
> gamut,
> > corresponding to RGB 0.899985 0.837122 1.000000
> > Target white value is XYZ 77.528580 81.568913 88.828359
> > Adjusted target black XYZ 0.34 0.35 0.40, Lab 3.88 0.45 -0.30
> > Target black after min adjust: XYZ 0.342 0.351 0.399, Lab 3.883 0.447
> -0.304
> > Gamma curve input offset = 0.000000, output offset = 0.004299, power =
> 0.000000
> > Total Iteration 3, Final Samples = 64 Final Repeat threshold = 0.600000
> > Creating initial calibration curves...
> > Doing iteration 1 with 16 sample points and repeat threshold of 1.200000
> DE
> > patch 16 of 16
> > Brightness error = -0.462568 cd/m^2 (is 81.106344, should be 81.568913)
> > White point error = 0.625266 deltaE
> > Maximum neutral error (@ 0.895486) = 1.116106 deltaE
> > Average neutral error = 0.685531 deltaE
> > Number of measurements taken = 26
> > Computing update to calibration curves...
> > Doing iteration 2 with 32 sample points and repeat threshold of 0.848528
> DE
> > patch 32 of 32
> > Brightness error = -0.322559 cd/m^2 (is 81.246354, should be 81.568913)
> > White point error = 0.646947 deltaE
> > Maximum neutral error (@ 0.248961) = 0.841565 deltaE
> > Average neutral error = 0.534482 deltaE
> > Number of measurements taken = 49
> > Computing update to calibration curves...
> > Doing iteration 3 with 64 sample points and repeat threshold of 0.600000
> DE
> > patch 64 of 64
> > Brightness error = -0.351730 cd/m^2 (is 81.217183, should be 81.568913)
> > White point error = 0.201203 deltaE
> > Maximum neutral error (@ 0.100647) = 0.920412 deltaE
> > Average neutral error = 0.409086 deltaE
> > Failed to meet target 0.600000 delta E, got worst case 0.559542
> > Number of measurements taken = 159
> > The instrument can be removed from the screen.
> > Written calibration file
> '/usr/share/color/icc/T61p-full-brightness-argyll-1.3.1-sRGB-D65.cal'
> > Luminance XYZ = 0.000000 79.468347 0.000000
> > White point XYZ = 0.951621 1.000000 1.047750
> > Black point XYZ = 0.004093 0.004148 0.004938
> > Created fast shaper/matrix profile
> '/usr/share/color/icc/T61p-full-brightness-argyll-1.3.1-sRGB-D65.icc'
> >
> > blackknight ~ # dispcal -yl -v -r
> > XRandR 1.2 is faulty - falling back to older extensions
> > Setting up the instrument
> > Instrument Type: ColorVision Spyder2
> > Serial Number: 00633553
> > Hardware version: 0x0307
> > Place instrument on test window.
> > Hit Esc or Q to give up, any other key to continue:
> > patch 3 of 3
> > Current calibration response:
> > Black level = 0.41 cd/m^2
> > White level = 80.85 cd/m^2
> > Aprox. gamma = 2.20
> > Contrast ratio = 196:1
> > White chromaticity coordinates 0.3122, 0.3277
> > White Correlated Color Temperature = 6541K, DE 2K to locus = 4.0
> > White Correlated Daylight Temperature = 6542K, DE 2K to locus = 0.7
> > White Visual Color Temperature = 6395K, DE 2K to locus = 3.9
> > White Visual Daylight Temperature = 6566K, DE 2K to locus = 0.7
> > The instrument can be removed from the screen.
>
> --
> Florian Höch
>
>
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