Originally Posted by H Stevens
There doesn't appear to be any consistency between calibration disc. If you take a gamma reading with the Chromapure disc, AVSHD and then GCD you will get three different results. Also, the results are different among window sizes and of course normal vs. APL.
Basically you're measuring how your display responds differently depending on the displayed image. If you were to use an LCD-based display with a fixed backlight, you would find that DVE and AVS HD 709 are in complete agreement within the limits of the meter and the stability of the backlight. In such a situation with a contact meter, the expectation is that it doesn't matter if you measure a field, a window of various sizes, or an APL series, because the patterns all contain the same digital information in the measurement area.
And the most puzzling is that none of the results from any of the disc will be close to the setting you selected in the user menu which is why, I assume, that calibrators set the gamma to 2.4 in the display when they want an end result of 2.2.
Again you're talking about the display, rather than the calibration pattern.
Also, in the past week or so, there has been an effort by some members, to create a set of patterns with a smaller window size, so that they can get an accurate reading with their plasma panels.
It's been discussed before, and personally I haven't seen data that suggests choosing a particular size window increases the correlation among various displays. If anyone had provided a data-backed argument I was willing to consider changing the window size, but I never saw anyone working on data that concentrated to show if a particular size window actually tended to bring various displays more into agreement. I don't see how it would, but I also don't care to concentrate on plasma or CRT displays.
Why isn't there a standard? Or is there one?
My cynical side says there's no standard because it might not be good for business if people really started concentrating on just how much observable display to display variation there can be after "calibration". My practical side says that as long as there are various displays that operate somewhat differently, the sort of accuracy people think they're achieving may not really be possible.
Shouldn't all of this have been ironed out along time ago or is it that most are using pattern generators and have not come across these issues?
Pattern generators have to conform to the same 8-bit world that they attempt to calibrate. From an end-user perspective they can't achieve anything that couldn't also be done with video.