Thanks for your detailed answer Peter. I will try to be as exact as possible in my reply.
Peter Karp schrieb:
iColor Display was tuned to give a visual good gray balance. Especially for the hardware calibrated Quato displays, which is the "main task" for iCD, it does a good job. You have not specified which blackpoint setting you have choosen for the iColor Display calibration. There is one setting to calibrate to the native blackpoint (meaning as dark as possible) or you can choose to calibrate to a specific blackpoint luminance with "neutral black".
The latter is the setting I use, neutral black with a target value of 0.0 cd/m^2. I think what it does then is try to achieve a black luminosity as low as possible without sacrificing neutral rendering. The results are quite good. The black point is measured to be about 0.11 cd/m^2, which is virtually no different to the black point luminosity without any calibration.
This setting will use the specified blackpoint and will try to match the blackpoints color temperature as close as possible to the whitepoint. This is similar to choose the "blending" in Argyll. But as Graeme said this is a trade off between a low black point and a more or less neutral color temperature in the shadows. In my experience a totally corrected black point is not needed and will result in a too high black point. "Too high" means here you will loose contrast. You won't see 1000K higher color temperature in the 0/0/0 black, when a little above (for non-zero RGB values) you will get close to the white point color temperature. You could upload or e-mail the generated profiles and other data files. That might be helpful to find the reason for your observations.
I will put links and descriptions to the various created profiles at the end of this message. I just took some readings with spotread using a canvas in Photoshop as a "patch". I will explain my procedure shortly: First, I filled the canvas with pure white and took a reading then to be used as the white point reference (Shift + a). Then, I filled the canvas with black and gradualy increased the luminosity in LAB space in steps of 10. The readings (Button a) are as follows (temperature values CCT):
000: 7838K 001: 5340K 002: 5570K 003: 6264K 004: 6391K 005: 6533K 010: 6257K 020: 6389K 030: 6396K 040: 6495K 050: 6420K 060: 6455K 080: 6513K 100: 6475KI have to say that readings below a L value of 5 were quite inconsistent. For example, the black point (L=a=b=0) was measured as
#1 XYZ: 0.091332 0.107938 0.132846 (08952K) #2 XYZ: 0.091332 0.091332 0.141149 (10218K) #3 XYZ: 0.099635 0.107938 0.132846 (07896K)These are three successive measurements. Of course, there are just very slight variations in the XYZ values but these result in huge differences in color temperature.
The calibration matrix used should not make a difference. Your Eizo uses a "sRGB"-panel type and iColor Display uses the LCD readings from the SDK. In this case no special calibration matrix is used, but the default X-Rite factory one for LCDs. I assume that Argyll also uses the LCD values and neither the raw measuremet data nor the CRT values. So the instrument readings should be similar.
That would also be my impression. Regarding the UGRA-Test you wrote:
It has some relevance but not in this regard you're trying to understand. It's a closed loop test and therefore the device will not tell you "absolute" truth you are looking for here. The test is useful to some extent, but because you normally won't know if your colorimeter the use is limted.
This is also what I thought, the test being a loop. Of course you can only proof that the profile created corresponds to the readings taken before and to what extend it is accurate in creating the gamut description.
I tried the download, but it didn't work (any longer?). On a related note: One idea I had and always wondered why nobody seemed to realize (at least AFAIK) is the option to specify for a so called software calibration (via vcgt) if the calibration curves should be smoothed, thus giving smoother gradients sacrificing a little bit of the profile accuracy.
Here is the link to the updated (and fixed) dispcal.exe: http://www.argyllcms.com/dispcal_win32.zip
After I created a profile, I normaly check out the results by browsing to two different locations on the web. The first one [1] renders a test image in which numbers are displayed with different neutral RGB values. Profiles generated with iColor produce results where all numbers are visible and none of them seems to have any color cast to the naked eye.You have to be extremly careful what you check with such a test picture. Does it use "raw" values or are ICC profiles used for the test picture and the monitor? Second you need to know that if you look if certain steps will be visible in a ramp is highly dependent on the ambient _and_ the gradation you used for the calibration. There's not a single "best" gradation.
The images I use have no embedded profile and are only interpreted through the installed monitor profile. I think Photoshop does not do any space conversions except for the one into the monitor space. As I understand it, this is the way I am able to see if a profile created shows any unwanted behaviour visible to the naked eye. Of course, this is a very limited test and not objective at all.
My settings for observer and ambient are the default ones used by Argyll. I ave yet to see a profile created with Argyll or iColor Display that would not show all numbers, so there has been no problem as of now.
Profiles created with Argyll also reveal every number, but there is a slight greenish or reddish hue on numbers on the dark area from 4 downwards.That's the interesting point here. Without having compared both solutions I guess the reason is the "resolution" (means number of measurements) in the shadow range which is used as the basis for the calibration (vcgt) curves.
I normally set the quality to high when using Argyll to calibrate the display which would only allow for a deviation of 0.6dE to the target value. I don't know how efficient Argyll does the job, but looking at the number of measurements taken alone should give Argyll an advantage in accuracy over iColor.
The second image I open is to see how many visible bands in a supposedly smooth gradient appear. Here, both programs produce profiles that show bandingWhich you will always have when you have a "software" calibration opposed to a hardware calibrated display. That's because of the limited 8Bit/channels resolution for the vcgt "calibration". You have an 8Bit/channels input signal, do some corrections in 8Bit/channels for the output. Then you will loose some levels due the inevitable roundoff errors. Smoothing the calibration curves should improve this to some extent. For example the default vcgt-curves for Apple displays (default ICC profile for Powerbook for example) are smoothed and produce a decent smooth gradient IMO. I don't know if Argyll supports such a smoothing. But you could do this "by hand": read out the vcgt curves (xcalib or X-Rites CalibrationTester might be helpful but I think in the Argyll files you also can see the calibration curves), import the values to Excel or somewhere else, smooth the function (or better said values representing the transfer function) and create a new profile including the smoothed calibration.
I understand that software calibration will always result in banding. But there are differences in various profiles created and I merely check if banding grows out of acceptable boundaries. I did and do not expect Argyll or iColor to create profiles without any banding at all. I know this is impossible with the current 8-Bit limitation and could only be done using hardware calibration (which Argyll does not support at all, as far as I know). I wonder if there are any plans in the industry to broaden the connection between graphic cards and displays to at least 10 or better yet 12 Bit per Channel. I sure hope so for the future.
Thanks for your time, I hope I could resolve any misunderstandings. Steffen Attached are links to the profiles and a quick explanation for each:[1] http://www.evilstiefel.de/pics/argyll/20080904_Eizo_Native_LinearVCGT.icm This is a profile created by Argyll skipping the dispcal utility and just profiling my screen using targen to create 2000 test patches, reading them in with dispread and using colprof to create the profile.
[2] http://www.evilstiefel.de/pics/argyll/20080909_Eizo_ProPhotoRGB.icmThis profile was created using iColor Display in reference mode using the recommendations for the ProPhotoRGB color space (6500K, Gamma 2.2)
[3] http://www.evilstiefel.de/pics/argyll/20080910_Eizo_22_Native.icmThe profile currently in use. I created it with Argyll, set to native white point (which is around 6480K) and a Gamma of 2.2. Creating a profile with a Gamma of 2.4 resulted in annoying gradient results in applications that don't support color management (of course this was just a matter of personal taste, but nevertheless). The new parameter A in dispcal was set to 3 and this time I chose 1000 test patches to be read in (with virtually no difference in accuracy to 2000 patches).
