Posts by przemhb

    I was wondering if PA246Q User Mode is still buggy, so I decided to test it by myself. As you may be interested in results and there are some questions regarding them I present results below.

    The test was performed with the monitor connected via DP to Radeon HD6600. Resolution was set to 1920x1200 and colour depth to 32bpp.
    Argyll CMS 1.3.4 and dispcalGUI were used. Huey Pro colorimeter along with correction matrix for the LM240WU4-SLB1 panel (derived by using ccmxmake utility from Argyll suite, Color Munki Design spectrophotometer and NEC SV241 monitor with the mentioned panel).

    Applied CCMX correction matrix:
    0.84308 -0.012484 0.028477
    0.023148 0.83371 -3.9284e-003
    -0.013409 0.025818 0.94938

    Tested PA246Q was produced in mid-April ("ISO week 14" according to EDID info).

    Calibration target was: sRGB, whitepoint 6500K, whitelevel 140cd/m2, native black point, ambient light level 136.6lux, profile type XYZ LUT + matrix.

    At first User Mode was selected and hardware calibration was performed. Contrast was left at it's default value (80), and brightness and RGB gains were adjusted to reach desired whitepoint and white level.

    Target Br 140.00, x 0.3128 , y 0.3291
    Current Br 140.37, x 0.3130-, y 0.3286+ DE 0.5 R- G++ B-

    Black = XYZ 0.19 0.20 0.29
    Red = XYZ 95.17 43.74 1.55
    Green = XYZ 20.26 65.53 8.72
    Blue = XYZ 27.68 10.18 146.95
    White = XYZ 131.36 138.14 150.93

    Sum = XYZ 1.042 1.060 0.8984 (normalized)

    Normalized sum of RY+GY+BY is close to 1 - 1.06. Normalized sum of RZ+GZ+BZ isn't close - 0.8984. Is it OK - I'm not sure.

    After calibration profiling was performed and profile quality was checked. Verification has shown average dE*76=0.61 and maximum dE*76=2.81 for verify_extended.ti1 (take a look at attached: verify_2011-09-05_18-10.html). For verify.ti1 it has shown 0.3 and 0.86 (take a look at attached: verify_2011-09-05_18-08.html).

    On one hand normalized sum of RZ+GZ+BZ is not close to 1, and on the other profile verification shows that the monitor's characteristics was captured correctly as if the user mode worked fine...

    Next colour accuracy was verified against sRGB IEC61966-2.1 simulation profile. Results were bit surprising - average dE*76=1.82 and maximum dE*76=10.9 (take a look at: verify_2011-09-05_18-13.html)! Why maximum dE*76 was so big?

    Then the monitor was calibrated and profiled from the Standard Mode. In the mode only white level could have been set to desired value.

    Target 140.00
    Current 141.52 -

    Black = XYZ 0.19 0.20 0.30
    Red = XYZ 83.84 38.07 1.38
    Green = XYZ 28.81 93.11 12.19
    Blue = XYZ 26.85 9.65 142.82
    White = XYZ 139.41 140.63 155.97

    Sum = XYZ 1.045 1.057 0.8985

    After calibration profiling was performed and profile quality was verified. Verification has shown average dE*76=0.60 and maximum dE*76=2.80 for verify_extended.ti1 (take a look at attached: verify_2011-09-05_19-03.html).
    Once again normalized sum of RZ+GZ+BZ is not close to 1, but profile verification shows that the monitor's characteristics was captured correctly.
    Next colour accuracy was verified against sRGB IEC61966-2.1 simulation profile. Results were even more surprising - average dE*76=1.84 and maximum dE*76 as high as 6.36 (take a look at: verify_2011-09-05_19-05.html)! Why maximum dE*76 was so big? calibration and profiling from Standard Mode was successful, and this one was not. Something seems to went wrong. But what?

    Is it the case of the panel chromacity spectrum discreepency between two different LM240WU4-SLB1 units causing CCMX correction matrix being inadequate for the particular panel used in the PA246Q tested?

    Revealed errors couldn't be results of some colours falling out of a gamut as all sRGB colours fall inside of the panel gamut.

    For more detailed results and log files look here .


    I have a few questions concerning Asus PA246Q banding mentioned in review. Here they are:

    1. You wrote: "In some colour spaces, however, faint banding is visible – also in the AdobeRGB image mode", but didn't mention any other colour space affected by banding. Could you tell me which colour spaces are affected by banding (apart from the mentioned AdobeRGB)? Did you mean sRGB at the point?

    2. You wrote: "After calibration and profiling of the Asus PA246Q from the standard image mode [...] Colour gradients demonstrate only very fine banding". Could you tell me what was effective bit depth of the Gainward GTX 560 LUT (for example Argyll is able to give such an information)? You have used DVI; was it 8-bit per colour or 10-bit per colour - could you tell that?

    3. Do you think that using DisplayPort 10 bit/colour connection and a graphic card with 10-bit effective bit depth resolution could eliminate the banding?

    4. Have Asus responded somehow to the User mode non-linearility flaw? Could it be fixed with a firmware update?

    Suppose I would compute correction matrices for some standard sRGB gamut sources like CRT and LCD and for a WCG-CCFL for my Huey Pro colorimeter (against good spectrometer like i1Photo Pro or ColorMunki Photo) and then I have used them accordingly during profilation of a monitor, esspecially WCG-CCFL one. Would it lead to consistent and good results?

    Are you going to check newer revisions of a Dell U2410 for the Custom Mode problem? I am wondering which monitor to choose - HP LP2475w or Dell U2410 for photo edition tasks.

    As far as I know U2410 has 8-bit+A-FRC panel LM240WU4-SLB1, 12-bit non-programmable LUT and accepts 10-bit input, and LP2475w has 8-bit panel without A-FRC - LM240WU4-SLA1, 10-bit LUT and 8-bit input (correct me if I'm wrong).
    In theory then U2410 should be able to produce finer gradations, and more precise colours in sRGB mode, but on the other hand malfunction of Custom Mode will force to use 10-bit (Radeon X1300) VCGT LUT. Which choice would you preffer?

    In a meantime I have noted that in Dell U2410 review you have stated:
    Currently, no software we know of officially supports the integration of individual correction matrices.

    Currently Argyll CMS supports correction matrices, and there are some correction matrices available for some colorimeter and wide gamut LCDs. Take a look here for more detailed information.

    So Tftcentral in fact shows how close profilation target was achieved - this is the way one should interpret their "calibration reports"; deltaE in fact is only difference between profilation target colour chromacity and the colour actual chromacity, is that right?
    In other words they should compare against sRGB or AdobeRGB (defined colour space) after profilation, as they do compare before calibration and profilation, right?

    My main point of interest regarding the monitor is whether it is the best under 600e wide-gamut choice for photo edition. According to your old review (comparison of calibration to sRGB with sRGB standard) it cannot achieve low dE for colours of sRGB target (after calibration and profilation to sRGB). Do you sustain that or do you think that a test according to your new procedure would show it is in fact capable to be calibrated and profiled so to achieve dE<2 for colours?

    As to the right probe - I understand you mean that most of the used probes has spectral sensitivity characteristics chosen for XYZ coordinates of the most popular sRGB colour space and so they are not precise for colours outside sRGB colour space, is that right?
    What if one would prepare a correction matrix for such a colorimeter - would it become capable of accurate measurements in, for example, AdobeRGB?
    (I do not know German language so I only guess that is what you may describing in the article you gave a link to).

    I would be very interested in a review of colorimeters. How accurate they are in sRGB space, how do they perform in AdobeRGB, maybe you could derive correction matrices for AdobeRGB, etc.
    I think you have got a good background for this task - I think of your own software and reference class colorimeter - UDACT.
    What do you think of the idea?

    If you compare Prad's HP LP2475w review with Tftcentral review you would notice that for exactly the same starting point of calibration (compare deltaE for uncalibrated 6500K mode, User Mode and sRGB mode from the two sources) after calibration to sRGB Tftcentral achieved excellent deltaE of 0.3 (max. 0.5) whilst Prad's sRGB calibration resulted in average deltaE of 3.7 and huge errors of 10 for green and cyan.

    There is clearly something wrong with the part of the Prad's review. Could someone explain it sensibly?

    I think it could be a good idea to update the part of the review.