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As I have posted in other threads, I am currently playing with the gamma tables on my Davis projector.


One thing I noticed is that it starts outputting light at just 1% IRE. If I watch a movie with a black background, that's at 7.5% IRE, and the blanked background from yxy is 0% IRE, and it's clear that they're different.


So, my plan was to compress the gamma ramp, by moving the 1% IRE point to 7.5% IRE. I would compress the light output values up until (I picked out of a hat) 20% IRE. So, if the output value went from 1 at 1% IRE to (say) 500 at 20% IRE, I changed it to go from 1 at 7.5% IRE to 500 at 20% IRE. So, in the 7.5 - 20 IRE range, it will start blacker (actually black), but have a steeper slope.


Anyway, I tried this, and watched the Matrix, and the dark scene in the beginning, I could see tons of video noise! I guess I was seeing lots of shadow detail - in fact more than what was actually there in the data signal!


Does anyone have any comments? Instead of doing the modification up to 20% IRE, I could do it over a wider range, say to 50% IRE, or even up to 100% IRE, and then the slope difference would be much less.


I *do* want my projector outputting nothing at 7.5% IRE, right? (I'm assuming my DVD is not in any kind of 0% IRE mode where it remaps 7.5% IRE to 0% IRE.)


Mike



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I can't comment on the IRE settings, but FWIW I've noticed that the opening sequence with Trinity has quite a bit of noise is the dark backgrounds. Particularly right at the beginning of chapter two. It's obvious on my (uncalibated) G15, and it's even pretty noticable on my (calibrated) 19" monitor.


So this particular case may actually be an issue with the source material, though non-ideally set gamma tables could certainly exacerbate it.
 
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