CurtPalme.com Home Theater Forum

[lyd]

I had been tweaking my brightness setting and the low-end gamma boost on the moome card using a couple of patterns comprised of nothing but sub-blacks to very dark grays. Like 2 to 24 in rgb, I think it is. Everything was looking great, since I got the tip to change that registry setting in PDVD.

Today I threw up a pattern that had a similar range of low values across the horizontal center, maybe about 50% of the height of the screen, and also had high spreads across the top and bottom 25%, intended for checking white clipping.

Looking at this pattern, all my low detail was gone. Black all the way through. If I adjusted brightness and/or gamma correction using this higher APL pattern, when I went back to look at the previous one with only very dark values I was seeing grays all the way down to like 4 RGB.

Is there something I can do to improve the shadow detail at higher average picture levels without destroying my inky blacks at lower ones?

lyd

[garyfritz]

That's the weakness of CRTs, especially if you have an AC model. That's called the ANSI contrast ratio -- the maximum difference between full-on and full-off on the same screen. ANSI contrast is tested with a checkerboard pattern, generally 4x4. In theory the black areas should be totally black, but because of light diffusion in the optics, light from the bright areas spills out into the black areas. If those black areas are dark shadow detail, the light from the bright areas can totally swamp them. That's what you're seeing.

Gamma boosting can help this, by raising the brightness level of areas that are greater than 0IRE. But in general you have to choose between "total fade-to-black, can't see my hand in front of my face, but I can't see any shadow detail when there are bright areas on the screen" and "I can see all the shadow detail, but the higher brightness setting means I only fade to gray," or somewhere in between.

[perisoft]

You could make software that's the anti-iris - boost gamma during high brightness scenes, drop it back during low ones. Heh.

[lyd]

[perisoft]

[ecrabb]

Sort of. The CLEV stuff is just dynamic contrast. In low contrast scenes, it expands contrast to "punch" up the image. It would actually exacerbate the effect you're seeing... or, it would at least make the scenes that you don't have a problem with more like the scenes that you do have a problem with.

ANSI... or intra-scene contrast... Deep subject. It's also worth noting this effect (the net result) anyway can happen in both the projector and in your own eyes. In a fully light-controlled environment, during low APL scenes your pupils will be fully dilated and you'll be very sensitive to small changes in the shadows. But, during high APL scenes, your iris constricts the pupil, and shadow detail will be much more difficult (or impossible) to discern. Try looking into a window on the side of a white house on a sunny day.

Anyway, what Perisoft is talking about is dynamic gamma... You could dynamically adjust low-IRE gamma as APL increases to compensate for both the projection system's ANSI contrast AND the eye's light response. Sounds like fun, eh? There are (or have been) people screwing around with that - without a doubt. Applied very subtly, it could be an interesting effect. The net result - if not applied very subtly - would probably look somewhat "weird" or "artificial" - kind of like HDR (high dynamic range) photography - which is somewhat related.

SC

[perisoft]

[lyd]

[lyd]

[perisoft]

[MikeEby]

[jask]

I was thinking the same thing! I would guess that you will be able to set up a better image from the HTPC if you pull the Moome out of the chain and redo everything from a HD test pattern.

[lyd]

[MikeEby]