What Gamma Curve Should I Use

R

rszebras

Well-known member
I'm having some difficulty controlling highlights without underexposing the rest of the image. The situation is this: I'm capturing in an area with overhead fluorescent and halogen lights. I'm not having a problem with any color cast. The problem I'm having is that the lighting is not consistent. So if I expose for highlights in the darker portion of the stage, when they move to the brighter area it's a difference of at least 20 to 30 IRE depending on the skin tone of the person and whether it's a woman with makeup -- GLARE and blown out highlights! The option of constantly changing the iris is not really an option.

So right now I'm using bpress gamma with the cine-like matrix. I tried adjusting the knee to low to reign in the bright areas but the other parts were underexposed when the speaker moved to those areas. So I think I need to switch to a different gamma curve. What is the best gamma for these situations? I want to expose the highlights of the skin at 60 IRE or so in the areas that are not directly under the lights but not face blown out highlights when they move five feet and are under one of the overhead lights. What gamma is recommended for this situation?
 
B.Press is probably the totally wrong gamma curve for that situation. You'd be much better off (I would think) with Cine-D. B.Press compresses the dynamic range and crushes the blacks, but cine-D stretches the dynamic range out a bit.


I would also think that you should explore DRS. DRS is not my favorite thing to do, because it can make the image noisy, but it's pretty much designed to cope with the situations you're experiencing. If you can run some tests on non-vital footage, experiment with DRS at all three levels, and view the footage back ON A BIGSCREEN TV, and see what you think. Depending on the camera you're using and the level of DRS, the effects can be mild or substantial, and the increase in noise could be minimal or massive. Maybe you'll find a happy medium you can live with that will solve your problem. Good luck!
 
Best gamma correction is to add some fill light to the darker arear so your exposure doesn't change so much. Even bouncing some fill from an overhead light off a sheet of foamcore might make enough difference.
If they are moving from shadow to light within one shot, why not expose so you don't blow highlights in the bright area and let the scene values fall a bit darker in the shadows anyway? This would look more natural and can add dramatic context to the scene.
Another option would be use a low contrast optical filter and split the difference on exposure settings.
Exercise more control over how the light affects your exposure rather than trying to correct only with camera settings.
 
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