GH4 gh4: highlights / shadows CURVE display accurate?

W

wwjd

Well-known member
Looking at the little graph in HIGHLIGHTS/SHADOWS settings, is shows little "curves"... one would ASSUME that is the actual shape of the curve: like shadow pinned at dark, bumping the low-mid, and pinned at center (center exposure?), but is that what it really does? IE the highlights seem to ROLL OFF nicely in the curve. It seems to help fake up DR, like many other tricks, just wondering if it is a linear deal or curved like they show?

How could one test that?
 
wwjd said:
Looking at the little graph in HIGHLIGHTS/SHADOWS settings, is shows little "curves"... one would ASSUME that is the actual shape of the curve: like shadow pinned at dark, bumping the low-mid, and pinned at center (center exposure?), but is that what it really does? IE the highlights seem to ROLL OFF nicely in the curve. It seems to help fake up DR, like many other tricks, just wondering if it is a linear deal or curved like they show?

How could one test that?
Click to expand...
I think the curve display is only an illustration, not tied to any real math...BUT...the adjustments are definitely applied as a curve of some sort. This is easily verified by shooting a chart with grey steps and measuring the non-linear response.

To stray into the area of personal opinion: I did a lot (way too much) testing of the Normal, Portrait, Natural and Cine-D profiles. Due to the nature of how the GH4 renders color, and how h264 compression works, using the highlight/shadow curves allows you to quickly make a nasty picture...especially in Cine-D, and especially in the "saved" highlights. (Really noticeable in skin tones.) I did find that a gentle s-curve, maybe +/- 2 ,could work nicely with some of the more full-bodied profiles like Portrait or Natural.
 
Roger. I'd read that from you and others also, and I never breach the +/- 2 mark.

Did you ever crank the HIGHLIGHTS down to -5 though? I've stretched some range with that but havent fully tested noise etc on it yet. I get ramping up the darks gets ugly, but think dropping the highs MIGHT be okay in some circumstances
 
wwjd said:
Roger. I'd read that from you and others also, and I never breach the +/- 2 mark.

Did you ever crank the HIGHLIGHTS down to -5 though? I've stretched some range with that but havent fully tested noise etc on it yet. I get ramping up the darks gets ugly, but think dropping the highs MIGHT be okay in some circumstances
Click to expand...
What you are likely to end-up with is yucky grey highlights, with no increase in headroom.

It looks like the cam adjusts the luminance without adjusting the color, but I think that's not exactly what's going on. I think it's a more complicated weakness in the processing. Because of the fast debayering algorithm, for instance...but that's just guessing on my part.
 
A lot of those controls were designed solely to help match to other cameras and never intended to help dial in looks. Plenty of people have attempted to push the GH4 in ways it just wasn't intended to do and the results are 100% never desirable. If you want true flat then use V-log and a cheap external recorder. Even a $295 Atomos Ninja that only records HD is a solid solution with the GH4 unless you absolutely need to deliver at 4k.
 
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