We need a lab test to determine the SNR in the last couple stops in HLG shadow area. It looks like HLG makes better use of the available bits than F-Log since F-Log has a much higher black level.
According to LUTcalc, HLG maps 18% grey to 22IRE while F-log maps it at 46IRE.
From what I have seen you don't gain any latitude switching from one to the other on the camera side (as opposed to the monitoring side), what you gain is increased color gamut in HLG. This means that the chroma values will be more present, it also means that when you hit the noise floor, HLG could appear to have more noise because the chroma noise will always appear more present than the standard log noise. So the S/R ratio might be the same, but in the HLG image it will appear more elevated after grading. However, if used properly, the increased color gamut can also help divert the viewers attention away from the noise in the shadows by shifting their focus to the added vibrancy in the highlights. So there is a part of this that is a perceptual difference, not just measured by SNR. The issue currently is that until more cameras implement 12 bit color space, they really are not taking the most advantage of HLG, so for the moment HLG and FLOG appear very close to each other.
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