Barry Goyette
 lvl.4
Flight distance : 14928 ft
United States
Offline
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Patrick -- Like almost all Log Gammas, D-LOG does show some noise in the shadow areas. I wouldn't call it excessive noise. I'd say its less noisy than most log gammas I've worked with from Canon, Sony and previous DJI versions of D=Log. By Design, LOG gammas are designed to give maximum dynamic range and flexibility in post by foregoing the tone compression that happens in the shadow and highlight areas of a typical rec709 linear gamma. Two factors are at work here: one is the LOG encoding itself which assigns relatively equal amounts of encoding values to each stop of dynamic range...and the second is by essentially "underexposing" the sensor to allow for maximum DR in the Highlights. DJI has determined, rightly, that ISO 500 is the best trade off between DR and noise. As Log gammas go...D-Log is pretty good, although DJI's lack of documentation, LUTs and propensity for changing it whenever they feel like it are slightly problematic.
The problem with the noise being "excessive" thus, falls to the user. If you're not used to LOG exposure, it's pretty common for people to expose "normally" and then complain about the noise in the image. Log exposures do best when the exposure is increased to the point where the brightest highlights are nearly clipping, often referred to as exposing to the right,( the reasoning behind it in LOG gammas is slightly different that why is is done conventionally with linear gammas, but the result is largely similar). Because of how LOG gammas are encoded, there is generally no penalty for exposing this way, and so, your goal is to use that extended DR to maximize exposure to the sensor (something difficult to do with linear gammas because of the compression mentioned earlier).
Your exposure in Log should generally look 1-2 stops brighter than normal, and when you process the image in post, as you mentioned, you pull everything down, including "crushing" that shadow detail which will eliminate or minimize the noise you are seeing. I recently did a test of a 3 stop exposure ramp with D-log where the darkest exposure had typical D-Log noise in the shadows, and the brightest simply had no noise at all....this was on a relatively challenging backlit scene with trees against a sky and dark shadows in the foreground. D-log had enough range to handle this with a 3 stop increase in exposure, and produce exceptionally clean results. The more dynamic range the scene has, the less you'll be able to ramp the exposure, but you should, generally increase it until important highlights are just below clipping. There are times when you'll have to compromise...for instance when the sun is in the shot...as 13 stops of DR won't let you see the sunspots and have clean shadows at the same time.
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lvl.3
Administrator
well said, barry!