Originally Posted by Mark Petersen
Boosting the RGB offsets above 0 is what kills on/off because it raises the black level significantly. Reducing lumen output a little will affect contrast much less so. How much less has to be determined.
I think they are independent from each other but lowering contrast does end up effectively doing the same thing as lowering lumens. This is what I found:
Setting the black level floor (via the RGB offset adjustments) and the peak white (via the RGB gains) determines the full dynamic range (and therefore contrast). The brightness and contrast adjustments just set where video level 16 and 235 fall within that range. So lets say the black level is elevated (via RGB offsets), lowering the brightness adjustment will have no affect on the black level and lowering it will simply crush blacks. Lowering the contrast adjustment will lower where 235 hits as far as lumen dynamic range so it affectively does the same thing to full whites as reducing the RGB gains, but not by the same mechanism.
If reduced lumen output does work out to be the way to go to get the CMS to track, it's worth playing around with both the contrast and RGB gains to see which may yield the best results.
It's a given that at the end of the chain there are three panels that have to do with 8 bit dynamic range (at best) to modulate the light output.
Within this available range the grascale and cms adjustments must operate without clipping the maximum inputted video level.
The white balance adjustment (grayscale) to get D6500 limits the dynamic range for blue and green due to weaker red from UHP lamp.
The $6000 question is are the CMS matrix calculations applied before or after the gray scale calculation in the projectors hardware/software implementation.
If CMS is applied after the white balance adjustments then the adjustment ranges in the cms for green and blue get reduced significantly.
(I guess roughly buy the same ratio of the lamps red to green light output ratio! 20..30%)
Example: grayscale may require green gain to be reduced by 30%
Gray scale is a relative adjustment while to move the green around in the gamut requires an absolute adjustment.
The cms adjustment range for green suffers because the green stimilus it has to work with is reduced by 30%
For blue it is the same but since blue is closer to the desired location in the gamut it is less of a problem.
This would be a major design flaw.
I think if this is the case the best way to proceed is to white balance the image with a red color filter to get the most dynamic range for green or blue (depending on which color is strongest). I suspect blue is a bit weaker than green so the trick is to balance blue and red with the color filter and get green in line with the gain control.
This should minimize the impact on lumens output and improve the black level.
(Minimizing the hit on the contrast ratio)
With the overal whiteness setting (contrast) it must be possible to adjust for the maximum light output before the panels max out.
Its widely accepted that accurate gray scale is are the expense of max lumens. (For UHP lamps with weaker reds that is.)
It seems that in a similar fashion accurate colors will be at the expense of the contrast ratio.