nome cognome wrote:
Spewctraview II is not a masterpiece, in fact if I run "dispcal -v -yl -t6500 -g2.2 -qu calibrazione" (after the hardware calibration performed with spectraview II) and I choose "2) White point (Color temperature, R,G,B, Gain/Contrast)" I get DE 2.7 which is not so good (I'm sure that Spectraview II performs hardware calibration, I used X-Ryte Calibration (LUT) Tester to see if the video card LUT was linear). Target Br 133.11, x 0.3128, y 0.3291 Current Br 133.09, x 0.3074, y 0.3246 DE 2.7 R++ G+ B-
Some monitor specific calibration systems use custom instrument calibration matrixes to achieve better accuracy from a colorimeter that it's default generic calibration, so the above discrepancy may actually reflect the inaccuracy of the generic instrument calibration matrix that Argyll has to use, rather than any deficiency in Spectraview.
So I decided to perform also a software calibration (my video card is an Ati Radeon HD 3870 which has a 10bit LUT). I typed "dispcal -v -yl -t6500 -g2.2 -qu calibrazione" again and I pressed 7 to continue on to calibration. I did a little test to see if if I have obtained benefits by adding Argyll software calibration: 1) Only hardware calibration + Argyll profiling targen -v -d3 -f200 -A.5 -c"LCD3090WQXi 88100898YB.icc" monitor_140_m_1 LCD3090WQXi 88100898YB.icc is the profile created with Spectraview II. dispwin -c dispread -v -yl monitor_140_1 colprof -v -qm -ni -no -np -as monitor_140_1 targen -v -w -d3 -e 1 -g 32 -f 320 -r check_monitor_140_1 I created a new test chart to avoid the use of the same patches used for profiling. dispread -v -yl check_monitor_140_1 profcheck -v -k -w check_monitor_140_1.ti3 monitor_140_1.icm > profcheck_monitor_140_1.log Profile check complete, errors(CIEDE2000): max. = 1.926604, avg. = 0.308265, RMS = 0.380178 With only the hardware calibration (which has DE 2.7) the average error is 0.3. 2) Hardware calibration + Argyll software calibration + Argyll profiling dispcal -v -yl -t6500 -g2.2 -qu calibrazione targen -v -d3 -f200 -A.5 -c"LCD3090WQXi 88100898YB.icc" monitor_140_2 dispread -v -yl -kcalibrazione_140.cal monitor_140_2 colprof -v -D"monitor_140_2" -qm -ni -no -np -as monitor_140_2 targen -v -w -d3 -e 1 -g 32 -f 320 -r check_monitor_140_2 dispread -v -yl -kcalibrazione_140.cal check_monitor_140_2 profcheck -v -k -w check_monitor_140_2.ti3 monitor_140_2.icm > profcheck_monitor_140_2.log Profile check complete, errors(CIEDE2000): max. = 1.972252, avg. = 0.802361, RMS = 0.838653 With hardware calibration (which has DE 2.7) + Argyll software calibration (Ultra quality) the average error is 0.8!
A couple of comments: 200 points is a small number for profiling, although it may be sufficient for a shaper/matrix profile. It's probably too small a number for verification checks though. 1000 would be better. I'm not sure why you are referring to the DE 2.7, which is the hardware calibration white point delta E, since the profiles will represent the behaviour of the device as it is, and hence are not affected by any absolute white point inaccuracy's. The shaper or gamma/matrix profiles have a deficiency in not perfectly fitting non-zero black device responses, and so the shaper/matrix profile fit may be influenced by the presence of hardware calibration. Without access to the device in order to look at all the details, it's hard to explain exactly why certain combination work as they do, but generally any DE under 1 is reasonable good. If higher fit accuracy was desired, I'd be using a LUT based profile (maybe using XYZ PCS) with a larger number of test patches (1000+), rather than a shaper/matrix profile.
Is this what should I expect? DE 2.7 is not a good result, so I thought that I would have gained color accuracy calibrating with Argyll before profiling.
Calibration mainly has benefits for non-color managed applications, such as windowing systems etc., and in making sure that basic parameters such as white point and brightness of decorative surround elements do not throw off color perception when viewing images using color managed applications. In the case of badly behaving devices calibration may make for better fitting profiles (particularly if matrix profiles are used), but if the display is already well behaved, then using two calibrations (one in the display and one on the display card) may add little advantage, or simply throw more randomness into the situation. Graeme Gill.