Originally Posted by alluringreality
Far as I can tell, he's saying that windows with a black background are magic, but maybe there is actual measurement data somewhere to support the opinion.
There is none, the argument stems mainly from historical inertia without any metrology basis. I summarize here my findings in a little easier to understand format regarding why one shouldn't calibrate plasmas with any pattern than generates less than ~5% average relative luminance[ARL] (to use Poynton's terminology).
These graphs were generated using 1% windows on fixed level backgrounds to produce the series of luminance levels plotted. At each level a 20 point grey scale run was performed to calculate gamma and dE. The background stimulus levels used were 0%, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, and 50%. [240 total measurements plus stability checks]
The chromaticity shift is relative to 10% windows on a 22% background and I've plotted the worst of the levels (30%). Using this dE scale it's equivalent to ~2 JNDs. This is in agreement with previous findings by both Tom H. and I that chromaticity shifts are less of an issue than gamma instability. However, both average gamma and the 30% level shifts in particular are significant in my opinion. That along with the fact that 99% of anything you will ever view will exceed 5% average luminance there is a good argument for avoiding windows on black backgrounds. There is another subtle effect regarding color saturation that occurs when using standard windows. Because they measure lower for gamma, the display will be adjusted to darken those levels and this in turn pushes colors towards the gamut edge. Not by much but it is measurable, about 1.5 dE94 for the red channel on my display.
note also that peak white was stable to within 2% at ~140 cd/m^2 for all runs, so the general perception that ABL plays a roll in these variations is false. In fact ABL plays little or no role in most of the video images you will encounter. Broadcast video and movies have average relative luminance
predominantly in the range of the "grey world" assumption 15%-18%
or lower. Plasma ABL circuits typically cut-in above 25% ARL
, which makes perfect sense from an engineering design perspective.Edited by zoyd - 8/22/13 at 4:47pm