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#1 Christopher Wedding

Christopher Wedding
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Posted 10 June 2006 - 10:09 PM

So I've tried to search around and I didn't find any concrete answer to what I was looking for in regards to gamma. Really, I'm gearing up to shoot some day for night stuff with the camera and I'm just trying to figure out what the best setting to go with this would be. Any suggestions would be mucho appreciated.

Also, more importantly, how does raising or lowering the gamma work exactly....right now it's at .45 if I raise it does that create more contrast or less, or what does it do exactly since I'm not clear on this?

Thanks for any help.

Chris
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#2 Christopher Wedding

Christopher Wedding
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Posted 11 June 2006 - 10:43 AM

Tough crowd....

OK, how about the part about whether a higher number gamma is more or less contrasty?

Chris
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#3 Michael Nash

Michael Nash
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Posted 11 June 2006 - 03:49 PM

Your post has barely been up for 12hrs, over a Saturday night. Give us a break! :P

Changing the Master Gamma on a video camera doesn't really change the contrast. What it does is make the midtones brighter or darker relative to the highlights and shadows. A gamma of .45 is considered "normal," .35 will yield brighter midtones and .50 will be darker.

"Gamma" and "contrast" aren't the same thing, although they're related. Contrast is the difference between light and dark values in the tonal range; gamma refers to the distribution of those values throughout the contrast range. Since video cameras have a kind of "lopsided" or uneven distribution of values (the highlight curve is steep and the shadow curve is flatter), sometimes you can use gamma and exposure to sort of "straighten out," or at least smooth out, that response curve. Raising the gamma up to .35 and underexposing a little can help you keep highlight values from getting away from you so quickly. But the trade-off is lower contrast through the midtones, and a somewhat more "pastel" looking image. You can fine tune the transition into shadows by raising or lowering the black stretch.

The pre-programmed "gamma mode" settings on the SDX (Filmlike 1 & 2) adjust the black stretch, master gamma, and knee functions for an overall gamma curve change. These seem to leave the level of midtones relatively constant, but do change the overall "contrast" characteristic of the image. With patience and a waveform monitor you can dial in your own custom curve that can perform as well or better than the pre-programmed ones, or you can modify the presets up to a point (Filmlike 2 defeats control over the knee, for example).

I'm not sure what settings would be best for "day for night," although I suppose the safest thing is to try to get as much detail in camera as possible. Protect the highlights and shadows equally for the most control in post. Just offhand I'd be inclined to keep whites from clipping at all costs, and expect to have to raise mids and shadows to compensate for the lower exposure. I'd look into lowering the knee point and slope as well. But the easiest way to learn it is to just get the camera and play with it. You'll see immediately the effect of changing the master gamma.

The SDX menus are almost identical to the Varicam, which are covered well here:

http://www.jkor.com/...ricampaint.html
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