GH4 V-LOG L noise reduction and color accuracy

Hi Brandon, I made a few tests myself and came to the conclusion that good internal V-Log footage should be shot 3 stops above zero. It leaves a bit of zebra when set on zebra 1. This is the best option to lessen the noise but keep some nice highlights. Do you think the Assassin would improve the noise of the sensor? Im considering it but i'm afraid it will make a difference in banding and artifacts.

I think the Assassin would definitely improve the quality of the encoding, it's not going to make noise go away. If anything, it'll be noisier. But there shouldn't be this magenta-shaded-breakdown on solid gray/brown colors.
 
What about when you film in HD at 200mbs? Has anyone tried that with V-LOG L yet? Does it handle the compression better? Sure, you lose 4K when you do that...

It's somewhat unrelated, but my experience of the 200mbps mode was actually a lower bit rate recording than the 100mbps mode, and certainly lower quality... Might test it again, could have been a previous firmware bug or something exclusive to my camera.

The 100mbps HD mode would definitely be a higher bit rate and like you said might be worth testing. I might have a go now.

I just tested this again and the "200mbps mode" gave me a file at 37mbps, and the "100mbps mode" gave me 87mbps. So stay away from the 200mbps mode. it looks like s*%t.
 
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Anyone have samples of the blocky magenta shadows to post?

Here it is at 8 bit, captured internally.

ZxXNGVL.jpg


And here it is at 10 bit, captured externally.

ayUDZT4.jpg


These are 1:1 extractions from the 4k frame.
 
I'm finding things clean up a lot if you put 18% gray at 55 to 62 IRE. Noise gets cleaner in both internal and 10bit output. I think pushing the exposure is the best solution to clean things up. Highlights around 80 IRE also looks good.

18% gray at 40 IRE was a mess.
 
I had finally time to play around with V-log and came to report the same issue. I don´t have YAGH, but the footage breaks apart easily. And yes always the same blotchy magenta and green.
I tried with all the exposures (over-exposure step by step until the max and under-exposure step by step until max and it was always present.)
 
I've had that magenta/green issue before using Natural and other default profiles. Has nothing to do with V-Log.

Correct, V-LOG L just exacerbates the compression problems the other profiles hide a bit better. It's one big Atomos Ninja Assassin advertisement! Haha.

Today I'm going to test filming in HD at 200mbs compression and see if it handles the V-LOG L any better. Probably not because it's still 8-bit, but it's half the pixels with double the bitrate - can't hurt! It'd be sad to lose 4K to shoot with V-LOG L but I'm gonna give it a shot...
 
Honestly it would be great if GH4 had one more firmware update that allowed you to import a LUT onto the V-LOG L profile and make that a custom profile. I mean you wouldn't have a super flat image, but you'd still have massive control over what the picture looks like, and the look would be applied before compression. Basically - I WANT FILMCONVERT IN MY CAMERA! Haha.
 
You mean like Canon had 6 years ago? Yeah, that would be nice. :)

Reading all the tech info above.... not sure where to set ZEBRA to expose but not exceed the sensor? Blow outs? Where to set ZEBRA for VLOG?
 
You mean like Canon had 6 years ago? Yeah, that would be nice. :)

Reading all the tech info above.... not sure where to set ZEBRA to expose but not exceed the sensor? Blow outs? Where to set ZEBRA for VLOG?

Right! I forgot about that. Man, if you could have some kind of computer interface to take the V-LOG L base and add LUTs to it, save it on an SD card and import it as a custom picture profile, I'd have an SD card for every film stock from FilmConvert!

As far as zebras - I've found the best thing to do is 50% Zebras for skin tones (caucasian skin should be zebra'ing at 50% for correct exposure) and 75% for overexposure indication.
 
Here's me not even trying to make this color blocking happen. Graded these to get them to match as close as possible for brightness and contrast.

First in V-log(0,0)--
by1.jpg


Then CineV (-1,-5,-5,-3,0), Shadow+3, idynamic low--
by2.jpg


Look at the window on the lower left.

V-log--
by1a.jpg


CineV--
by2a.jpg


As you can see, under the same normal circumstances, V-log creates this color blocking where other profiles do not. Also, I'm noting a slight green tint on Vlog footage, where my CineV settings color looks dead accurate. I used the stock daylight WB setting on both shots.
 
Look at the cabinet. It's supposed to be cream coloured, not blotchy magenta and green.

block1.jpg
Thanks for the frame grab, it's a good example of the pitfalls of sacrificing tonal range for the sake of increased dynamic range. The problem with the white cabinets is that the encoder has to apply the selected color temperature to a smooth monochromatic gradient, using 8-bit YUV components. It winds up dithering the gradient across the midpoint of the green-magenta axis, because it doesn't have deep enough hue granularity to render the gradient in pure tones and has no idea that the cabinet is "supposed to be white". This is also the cause of blotchy magenta casts in shadow areas - the encoder lacks the bit-depth needed to render subtle shades of near-gray gradients accurately enough to avoid color casts. The most natural-looking fix is to use secondaries in post to turn down the saturation in troublesome areas.
 
Here's me not even trying to make this color blocking happen. Graded these to get them to match as close as possible for brightness and contrast.

First in V-log(0,0)--
by1.jpg


Then CineV (-1,-5,-5,-3,0), Shadow+3, idynamic low--
by2.jpg


Look at the window on the lower left.

V-log--
by1a.jpg


CineV--
by2a.jpg


As you can see, under the same normal circumstances, V-log creates this color blocking where other profiles do not. Also, I'm noting a slight green tint on Vlog footage, where my CineV settings color looks dead accurate. I used the stock daylight WB setting on both shots.

I'm seeing magenta on the second picture in the same spot, albeit less of it.
 
it's your grading procedure. V-log needs to be interpreted properly or you will introduce this artifacting. The Varicam LUT does not do a very good job, neither do any of the BMD LUTs, Cineon is too dense. Try "S-log to linear" and correct for the greencast, and then match there's a good chance you won't see this. Or wait for me to release my custom conversion LUTs, but I'm not having this problem at all, unless I try to grade by hand or use the other LUTs
 
so apart from the magenta and green blocks, what do you guys think about the overall noise in the shadows and blacks? I filmed a skateboarder at the skatepark, high contrast sunny skies, he was wearing black pants... the noise on the pants is really bad (and I tried diff exposures) total showstopper for me. Using software maybe, but the noise is too heavy and will suck the life out of the footage
 
it's your grading procedure. V-log needs to be interpreted properly or you will introduce this artifacting. The Varicam LUT does not do a very good job, neither do any of the BMD LUTs, Cineon is too dense. Try "S-log to linear" and correct for the greencast, and then match there's a good chance you won't see this. Or wait for me to release my custom conversion LUTs, but I'm not having this problem at all, unless I try to grade by hand or use the other LUTs


Can you show some examples ?
 
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