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Exposing skin tones on V-log L profile

clyde villegas

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In both, I'm referring to filming with a Panasonic GH5 on V-Log L


1. Why do we need correct exposure for a particular log? Do colors shift when using wrong IRE? Or is it more for retaining details, not colors?


2. I've seen someone on Youtube (can't remember exactly who) saying that to get proper exposure on V-logL, your subject should be at 42 IRE. Using an 18% gray card, he adjusted the exposure until it's roughly 42 IRE. So i thought to myself that I can adjust exposure even when the subject/actor hasn't arrived on the set yet. I'll hold an 18% gray card on where his face would be and put it at 42 IRE on my waveform (or false color monitor).


However, I've read somewhere that IRE is different for different skin tones, like 55 for caucasians.


So, should I just expose my grey card to 42 IRE of just wait for the actor to arrive and expose for his skin tone? Which one is correct? Thanks advance! God bless.

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Colors don't shift when shooting LOG, unless you clip or expose one color beyond the range of the recording. For example, if you clip the blue channel highlights, but not the red or green channels, your highlights will shift to yellow.


As for other color shifts involving LOG recording, it's not in the recording itself, but in the transform from LOG, to let's say, REC709 by the use of a LUT. A LUT works by "if the recorded color at this pixel is "x", transform to "y". So, it's I guess possible that you might see some shifts as your exposure moves out of the range expected by the LUT.


But this can be fixed by adjusting the "exposure" of the LOG image before conversion by the LUT. This is done by "offset" in color correction. "Offset" simply adds or subtracts the same value from each recorded photosite. Using this function you can bring the image exposure back into the range that the LUT was designed for.


And, in fact, this is the proper way to use a LOG conversion LUT in color correction. There should be an exposure/contrast adjustment before the LUT conversion, and usually, some color correction performed after the LUT conversion to your output color space (REC709 or P3 etc).


There is no "proper" exposure for skin tones. That's part of the art of cinematography itself.


As for YouTube video tutorials... There's a lot of misinformation out there. If you own the camera, design your own tests and use the free version of Davinci Resolve to check the results. But, yes, you'll need to learn a bit of the software to do this and it will take some time.


There is a lot to learn here technically, and unfortunately, I don't know of a comprehensive book that teaches all of this. So, you will end up "googling" quite a bit and bumping into a bit of misinformation. Personally, I began by first learning Photoshop (took about a year!), and applied that knowledge to digital cinema cameras. It also helps a lot to have a professional color chart for testing purposes. Good luck!!!!

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