Ted, I totally agree. But if you think that verification of the pattern generator is important than you will surely also agree that a manual measurement of the exact same series of patterns should give the exact same result as the automatic measurement? Being able to do reliable, repeatable measurement is as essential as verifying the accuracy of the pattern generator vs the actual source used, if you ask me.
As Dominic points out correctly, I simply cannot reproduce the same gamma result when using the greyscale auto run vs doing the exact same but then by pressing the measure button for each pattern with my own hands, whatever I try. This is problematic.
Because the manual mode briefly (half a second, I am quick
) shows the chromecast homescreen (a dimmed photo) between every measurement patch and the auto mode jumps directly from patch to patch, one would suspect it has something to do with local heating of the test spot.
As you know with an OLED (at least an LG OLED) the output gets brighter the longer you leave a bright patch on the screen, it is not constant in time. When you do an auto-greyscale run, there is always a grey patch visible without any pause in between, which of course causes the panel to heat more and more during the course of the measurement. Even those 60 seconds of measurement time for a 20-point greyscale is enough to distort the result a bit because the last, brightest patches will be the ones that will deviate the most due to the heat that has been building up. After the panel cools a bit and you repeat say the 100% measurement it will be a bit lower. The more it cools the lower it gets.
However, there seems to be more to it than just heating of the panel, because as you can see even in the low regions (5%-30%) there is clearly a difference in the gamma graph. As much as I do not want to believe that HCFR is the source of the problem, if the first 5% grey measurements are already different using the manual vs auto method, the tv has no way of "knowing" if the mode is manual or auto since it is only the first measurement...
So I am stil torn between HCFR and the tv for the cause of this. Anyway, the distinct and repetitive stepping pattern does show that there is something not reacting very linear, either in HCFR or in the tv.
I am not sure how to get to the cause of this problem. I am now even planning to let HCFR do an auto run and then measure each patch simultaneously with a second meter and a diffent program to verify if the patch itself is off or just the value reported by HCFR. Or do an "auto" HCFR run and force a different image between every test patch: increasing the latency of the measurement to a high value would give me enough time switch to a different source between every measurement, thus refreshing the image in between patches.
(By the way, I have run a lot of tests already and compared and verified the results of my pc, the chromecast and using your and some other (GCD) test pattern disk with the internal player and also a Blu-ray player connected via HDMI3. The greyscale results using these sources are very close, so close even that I could suffice using the same settings for these sources.)