Rami Mustakim
Well-known member
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- Jan 10, 2008
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There's noise that seems to come from black shading problems, and then there is the basic noise related to exposure. Assuming you have done the black shading correctly, then it should be easy to test the camera to find an ISO setting & noise level that you can live with.
I think there are two areas that burn people -- one is overall underexposure and the other is lifting or brightening the blacks in post in an attempt to find detail in there, in other words, not using the right amount of fill light in order to keep your black level set normally for the expected noise level at that ISO setting. Because if you've tested the camera and found that the overall noise level, when viewing the image with the intended gamma for the contrast you want, is good at, let's say 800 ISO, it shouldn't matter if the actor steps in front of a black curtain or turns off the lights in the room within the shot, etc. It would only get bad if your exposure was too low and you tried to brighten the image in post, or the shadows were too dark and you tried to lift them in post. In either case, you are defacto rating the camera at a higher ISO, at least for the shadows, and thus getting noise.
Since the opposite is true, that darkening the overall image or shadows will reduce noise, then one solution is to give the image a decent exposure as long as you aren't clipping your highlights. Or use a bit more fill in the shadows and then lower the black level in post to compensate. Or use a lower ISO setting.
If you shoot some tests, have a black reference in the frame or try putting the lens cap over the lens at the end of the take, you can't get much blacker than that.
Also keep in mind that since visibility of noise in the shadows is related to black level, you should view your tests both in log gamma in order to see everything in the shadows, knowing that the noise in the blacks will be the most obvious, and then also in the final display gamma so that you see the black level and noise that can be seen in the shadows for the final image. Because I think some people are expecting completely noiseless images even when viewing log, which is not realistic -- I mean, you could get that with a lot of exposure and clips highlights, but then what's the point, you've got an unattractive image that happens to be noise-free.
From shooting film and relying on a light meter, I found that one has to "know oneself" in terms of exposure tendencies. I think after years of color-correcting your work, you tend to find out if you err (and everyone errs) on the side of more or less exposure. Knowing this, you can counteract your tendency -- for example, if you tend to make mistakes by underexposing, you probably should work at a lower ISO to begin with. If you tend to err on the side of clipping highlights, you might try working at a higher ISO. If you tend to not use enough fill light, you might try a display LUT that crushes your blacks a little, forcing you to add more fill to compensate (as long as you are aware you are hiding the noise more on the monitor by doing that.) Or you might want to get into the habit of toggling between a display LUT and seeing raw/log.