[argyllcms] Re: Wrong gamma / color rendition worse than before calibration
- From: "Thomas Bartosik" <tbartdev@xxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 08 Sep 2011 16:50:46 +0200
Graeme Gill wrote:
> It seems that by changing the white point from something near the native white
> to 6.5K you have reduced the brightness using the LUTs. That will loose you
> contrast
> ratio and steps. You could avoid this by using the native white point,
> or at least a white point closer to the native white point.
> Graeme Gill.
Tried that as I suspected it last night. I also set the gamma to the measured
one of the uncalibrated display: 2.29; no improvement...
Regarding Florian's comments:
Florian Höch wrote:
> Am 07.09.2011 20:18, schrieb Thomas Bartosik:
> > 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°...)
>
> A good viewing angle might indicate a PVA or even IPS type panel, but
> those are seen rarely in mobile computers. A brief search for the T61p
> panel specs didn't turn up much, so I concluded (maybe wrongly) it's a
> TN panel.
>
> > I think you're the one to know this better...
>
> Not necessarily, as I don't have a T61p :)
I also did a lot of research and only found out it's a LG-Philips
LP154WU1(TL)(B1), but found no spec sheet for it...
>
> > 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?
>
> Probably the former (my attempt at explanation below).
>
> > I mean before calibrating and profiling I could at least differentiate
> more color nuances than afterwards. This is somewhat strange.
>
> Not strange at all: Without the profile, the gamut of everything that is
> viewed on screen is squashed down to the comparably small gamut of it,
> leaving nuances intact, but at the expense of saturation.
>
> > What IS better after calibrating and profiling?
>
> All colors that are in-gamut will (or should) match better after
> profiling.
>
> To get some numbers how the screen copes with e.g. sRGB source material,
> you could use dispcalGUI's profile check feature:
> First, select the profile you want to test under "Settings".
> Then choose "Verify profile" from the "Tools" menu.
> In the file dialog, select "sRGB.icm" as simulation profile.
> In the next dialog, select one of the "verify" testcharts.
> Finally, you'll be asked to choose a name and location to save the
> report under.
> After the measurements, you'll get a graphical report with the color
> patches, expected vs. measured values, Delta E numbers and bar graphs.
> It'll probably be quite red (ie. bad) because of the screen's small
> gamut though.
I'll definitely try that. But isn't verifying a screen that's been
calibrated/profiled with a possibly erratic colorimeter with the same
colorimeter only going to give the same (bad) results?
I think it all boils down to this:
How I can trust in the calibrated/profiled look of the display? I think I could
only cross-check with another colorimeter and the probability of the result
being correcty should be higher if the two measurements do not differ too much.
>
> > 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?
>
> Are we only talking about calibration (tone curve and white point
> adjustment), or also in conjunction with the profile (and software that
> actually uses the profile)?
Both. My desktop looks ugly after loading the .icc profile and if i put the icc
profile to use in a color managed app it gets even 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.
>
> Those depend on the tone curve that is chosen upon calibration. Judging
> from looking at the calibration curves, I'd assume the native response
> of the screen is maybe closer to 1.9ish than 2.2 in the lower end
> towards black (but it's obviously only a wild guess on my part).
The spyder 2 measures an uncalibrated 2.29 overall gamma.. Should I try with
1.9?
>
> > 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?
>
> The filters in most colorimeters degrade over time, so it can't be
> completely ruled out.
Another fact that does not make things easier ;-)
Maybe we can come to some standard so we can compare things?
I've just profiled a DELL 2405FPW, which - according to tests here:
http://www.tftcentral.co.uk/reviews/spyder2express.htm
(when using the LaCie hardware) has more or less sRGB gamut.
Guess what? The result is also disappointing. But reading the article
referenced strongly gives me the feeling that the spyder2 is to blame.
The .icc and .cal files are at
rockbrew.com/argyll
again.
Compare them to the ones posted at
http://www.tftcentral.co.uk/articles/icc_profiles.htm
and they are largely different again.
so either all my displays are bad or my spyder is bad.
My nvidia-settings tell me I should use 6bit dithering for my t61p panel so I
guess you're right - it's a TN.
Any directions on what to do now - is the spyder really to blame? Am I doing
something wrong?
Can this be the filter/should I try to calibrate a CRT without the filter (or
would I even get a new filter for the spyder?)
Guess I'll soon be buying a new colorimeter - preferably one that's
future-proof i.e. WCG and LED backlight capable. Any suggestions? Should be
cheap but give acceptable results - i.e. FAR better than the spyder...
Or I'll save on the colorimeter and get a Lenovo W notebook...
>
> > 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
> >>
> >>
> >
>
> --
> Florian Höch
>
>
--
NEU: FreePhone - 0ct/min Handyspartarif mit Geld-zurück-Garantie!
Jetzt informieren: http://www.gmx.net/de/go/freephone
Other related posts:
