Basically Zoyd is using a 1% window for all the "APL" measurements, but instead of using a black background he's using the background to set average video level. There is a bit of change in his "APL" measurement series, but I would consider it rather minimal, especially since he's averaging the entire gamma run to one value. Between a pattern to measure black and a pattern to measure white, the average of the video levels on his patterns change by the window size of 1%, and a gamma-adjusted average level expected at the screen also only changes by 1%. Even on displays that are the most sensitive to changes in screen brightness, since Zoyd is averaging gamma to a single value, I would generally expect to see minimal difference in gamma measurements against a pattern that truly holds a constant screen brightness during the gamma measurement run.
To test that theory, I compared the "2% window" gamma graph against the "DB Ramp Dark" gamma graph in Chad B's PDF (http://www.avsforum.com/t/1446386/abl-effects-measured-for-comparison
). They are generally both very dark measurement series, as shown in their similarly high "Y Max fL" numbers. The "2% window" measurements have twice the variation in average video level and gamma-adjusted average level when compared to Zoyd's patterns, because the windows have twice the area. On the other hand the "DB Ramp Dark" has zero change in average video level or gamma-adjusted average level for the gamma measurement series. The "2% window" and "DB Ramp Dark" ramp graphs share a similar shape, and if the gamma measurements were each averaged to a single value there would be little difference between the "2% window" and "DB Ramp Dark" ramp gamma measurements. If Chad B had done a 1% window measurement, which is the measurement area size Zoyd is using, I would suggest there probably would have been even less variation against the "DB Ramp Dark" gamma, especially when each gamma graph was averaged to a single value. My main point here is to say that Zoyd's patterns likely measure gamma very close to using any type of measurement that holds a constant on-screen image - grayscale bars, AVS HD 709 APL patterns, Chad B's APL (http://www.avsforum.com/t/1445226/chad-bs-custom-test-patterns
I cannot say how exactly some publicly-available patterns like Chad B's APL (http://www.avsforum.com/t/1445226/chad-bs-custom-test-patterns
), "AVS S APL", or "AVS L APL" would relate to Zoyd's measurements, but I would suggest that their gamma measurements likely have some correlation to the measurements that Zoyd is taking. I get the impression that Zoyd thinks average video level is most relevant when it comes to plasma. My opinion is highly based on other display types, which can clearly vary light output while average video level remains constant, so I like to also look at ideal gamma-adjusted levels at the screen. From the data I've seen on plasma I get the impression that the information doesn't strictly tie average video levels to how the display operates, so I tend to think of patterns that only try to hold average video level constant as likely no better for gamma measurements than typical windows, even on plasma. Like I was basically saying in post #153, all "APL" patterns are not created equal, but patterns like the following probably tend to share some similarities for gamma measurements.
Publicly-available gray patterns for constant on-screen measurements:
AVS L APL - 36% average video level or 25% gamma-adjusted average level
Chad B's APL - 19% average video level or 13% gamma-adjusted average level
AVS S APL - 7% average video level or 5% gamma-adjusted average level
Zoyd's patterns that probably exhibit similarities to constant on-screen measurements:
40% APL - 40% average video level or 13% gamma-adjusted average level
27% APL - 27% average video level or 6% gamma-adjusted average level
22% APL - 22% average video level or 4% gamma-adjusted average level
Note: The levels listed here are all approximations, and 2.2 gamma was used for the gamma-adjusted approximation
My guess is that I suspect Zoyd's "22% APL" is probably darker than a lot of typical video content, but it would be interesting to at least see how the individual gamma measurements for his "22% APL" and "40% APL" patterns compare against Chad B's APL. The reason I would like to see a comparison of these three patterns is because the Chad B's APL has an average video level that isn't too different from Zoyd's "22% APL", while the gamma-adjusted average level for Chad B's APL is similar to Zoyd's "40% APL". I'm not sure if either average video level or gamma-adjusted average level can necessarily predict display performance, so I would guess gamma on Chad B's APL might fall somewhere between Zoyd's "22% APL" and "40% APL" patterns. My guesses have turned up to be completely wrong at various times in the past, but I would consider it interesting to see how gamma on Chad B's APL compares against Zoyd's "22% APL" and "40% APL" patterns on one of these two displays with the most posted information.Edited by alluringreality - 2/10/13 at 1:09pm