Adjusting Gamma Question

Stumbly wrote on 4/28/2003, 6:30 PM

When I adjust the gamma (brighter) of my letterboxed clips, the black crop gets brighter too-- ostensibly because the black of the crop is not truly at 0, but 7.5. What's the best way to tweak my gamma on a scene like this without affecting the crop? Is there a way to remove the setup, adjust the gamma, then add the setup back in? Or is there a better way, short of adding a masking layer? Thanks!
Mike

Comments

SonyDennis wrote on 4/29/2003, 2:57 PM

You've got the math right, but the terms wrong. 7.5 IRE setup is an analog issue, and does not need to be dealt with in the digital domain, except to compensate for captures that didn't properly remove setup.

What you're seeing is that fact that DV blacks are at 16, and these are being adjusted by the gamma adjustment, which is the correct thing for it to be doing.

While you could do some level offseting pre- and post-gamma to work around this, another solution would be to use pan/crop to re-clip your letterboxed footage so that the letterbox area is true black.

///d@