Originally Posted by PlasmaPZ80U
regarding the bit about plasmas, is the difference due to ABL and the effect it has on gamma readings?
The gamma measurements from the PDF at http://www.avsforum.com/t/1446386/abl-effects-measured-for-comparison
support the idea that LCD-based displays with a fixed backlight or iris can measure somewhat differently from plasma displays. Generally LCD-based displays using a fixed backlight are expected to measure gamma with little variation, regardless of the measurement pattern, so with LCD the typical expectation is that a tiny window or a full field will return a nearly-identical gamma graph. On the other hand plasma can have more variation in the resulting gamma graph depending on the displayed images, as shown in the linked PDF. In the link Light Illusion suggests that studio monitors measure more like LCD with a fixed backlight, but personally I don't have any experience with studio monitors to say how well they avoid some of the measurement differences found on consumer displays.
To keep things simple, I'm going to somewhat arbitrarily pick two graphs from the PDF and compare the gamma measurements. I'll select one window measurement run, because windows are the most common historical reference when it comes to discussing gamma measurements. I'll also select a constant on-screen measurement, because grayscale bar patterns have also been around for a long time, and because a constant image reflects the basic purpose of gamma as summarized in http://www.poynton.com/PDFs/GammaFAQ.pdf
question 5. A lot of people seem enamored with using small windows on plasma so I'll choose the 5% window gamma measurement, and for another pattern that's also generally darker than typical video content I'll select the AVS S APL measurement. The 5% window and AVS S APL also happen to have Y Max fL numbers that are somewhat close on the given display.
The general trend in the PDF is that the 5% window gamma measures lower than the AVS S APL gamma. I would suggest that, on the given plasma, the gamma you observe on-screen (AVS S APL measurement) likely tends to be higher than the gamma represented using a 5% window measurement. If you were to measure both the 5% window and AVS S APL patterns on an LCD with a fixed backlight, you would instead expect to get only one gamma graph with either pattern. So with the given plasma you can generally expect the on-screen gamma to be higher than the window measurement, but with the LCD the expectation is for the on-screen gamma to match the window measurement. From this premise let's say you measure both the given plasma and a fixed-backlight LCD using 5% windows, and you "calibrate" both displays so that they each precisely give a 2.2 gamma measurement. I would suggest that the measurements in the linked PDF suggest that if you view these two "calibrated" displays side by side on a somewhat dark scene the on-screen gamma for the plasma would probably tend to be higher than on the LCD. You could instead "calibrate" both displays to the same gamma using the AVS S APL pattern, and they might come closer to looking more similar in regards to gamma on a dark scene, but the other measurements in the PDF suggest the two displays would still have performance differences.