A7s and 8bit banding

S

Shirozina

Well-known member
First post here and hope this doesn't sound like a rant.....
It was a bit of a shock coming from the creamy smooth and malleable 10bit BMPCC files to find that blue and grey skies fall apart so easily on the A7s. Even shooting Cine profiles so you don't have to expand the tones in grading doesn't help much and infact the noise when shooting SLOG2 at 3200 or even 6400 helps over the smoother low ISO 's available in the Cine profiles. I didn't see this issue get mentioned when I did my research and lots were saying banding is not an issue due to the high bitrate files but I never saw banding as severe as this even with my 5D2 / Cinestyle or GH3. I wanted full frame to shoot architecture with my Canon shift lenses alongside my stills on the A7r but this idea is now looking unworkable. Besides adding noise in post, shooting high ISO or painting in skies in AE has anyone found any other practical workarounds? I'm thinking that maybe exposing +2 EV in SLOG2 may not be a be a good idea in situations where there are smooth gradients as noise IS necessary to control banding. Any possible advantage to shooting with 4k with the Shogun in this respect. What are the chances the A7sII will have 10bit - my thinking is that they wouldn't even if they could as it would eat a chunk out of their high end movie cameras.
 
Welcome to the club. Actually, there are a lot of us who think s-log2 is bad-to-unusable on the A7s.

The implementation of s-log2 in the A7s shares some bad characteristics with CineStyle. But the s-log2 in A7s has a couple of more issues compared to CineStyle: more DR and not using the top end of the coding range. Well, at least the A7s has a better codec. In any case, CineStyle had the excuse of being specifically designed to match curve with film scan workflows. I don't know what the excuse for the s-log2 implementation in the A7s is. Probably Sony didn't care enough to bother designing a specific curve for the photo cameras.

I am not too keen on noisy source footage. Source noise may help preserve detail (needs testing in this particular case), but the codec seems to be pumping data out at a constant bitrate, so not sure if you gain detail. And if you need to mask banding it might be better to add noise/grain in post.

Overexposing s-log2 2 stops is pointless. You lose all the highlights latitude advatange over Cine. Imo, the best approach with the A7s is to shoot Cine4 and expose properly. I've measured Cine4 clipping at +4 1/3 stops above midgrey; you can also see 4 stops quoted around, a variation in measuring methodology most likely. Underexposing up to 1/2 stop is also usable and brings DR up approximately equal to s-log2 overexposed 1 stop. In order to get the maximum out of this you need to flatten the low end of the curve and also lower black level down to -15 to expand the coding range.

The benefit of shooting this way is you get a relatively flat curve but with approx. full coding range used - no waste as with s-log2; plus, the slight whites compression above knee with Cine4 actually improves mid range density.
 
Thanks cpc. I'll have a go with Cine 4 ( and get to use custom WB!) - any links to a full settings list for this profile?
 
For $2500, a manufacturer has to choose their battles wisely. These things are DIRT CHEAP for what you get.
 
Shirozina said:
Thanks cpc. I'll have a go with Cine 4 ( and get to use custom WB!) - any links to a full settings list for this profile?
Click to expand...

Gamma: Cine4
Black Level: -15
Black Gamma Range: Wide
Black Gamma Level: +7
Detail Level: -7

You can use a Color Mode that you like. Cinema, Pro and Movie are all fine, with subtle (and no so subtle) differences. If you are going to use luts or grading tools that compress the color space, you may want to skip Movie as it is the most compressed of the three already. Also play with Color Phase to move skin from yellow to magenta. FWIW, I have my camera set to Color Mode Pro and Color Depth Red +4. (You may want to pull Color Phase to -1 in this case as skin may be very slightly on the pink side.) In any case, the color settings depend on your preferences.
Detail is unrelated to the curve, but having it all the way down may help with artifacts that people around here like to call "highlights aliasing" (they have nothing to do with aliasing though).

Edit:
Note that these settings are meant for grading.
In terms of max quality nothing beats shooting with end result tone curve in camera. Play with the Creative Styles (enabled by setting Picture Profile to off), they have good (and contrast adjustable) curves. Also, you can use the DRO option to flatten the low-to-mid range of the creative styles, should you wish.
 
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I only really see noise in slog2 in 4k in under-exposed areas, not a ton throughout the image, and the noise that is there seems pretty natural when playing back at full speed (sure when you pause you can nitpick). i use neatvideo already for denoising footage (the red dragon and bm4k see noise at even 800 iso), so if i see something noticeable from my a7s i'll apply around 30% denoise or so.
if cine4 works for you, great! a lot of people like it and i hope it solves your problems.
as for banding... it's not been significant, though i remember when shooting on my 5D i'd just add a small amount of blur to the sky to fix it.
here is a screen grab i did from a shoot this weekend. other than using the lut's i shot with and adjusting contrast, it's pretty much straight out of camera (ie. no debanding):

FD_07.jpg

i suppose if you zoom in a bit on the sky you might see some small gradation banding, though when moving i think you'd be hard pressed to notice it at all.
(the uploaded version is a bit compressed, some larger jpges on my site from that shoot can be found here if you want a better look)
 
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yeah her skin was severely underexposed, so i'm not super surprised there isn't a ton of detail, would cine4 be better for that in your opinion?
in my experience, film handles it somewhat similarly, and that typically gets scanned in with a lot of bits :) we usually fix it by windowing the face, pumping up the brightness and often adding a bit of warmth. (unless of course you want it to be underexposed)
 
Well, you can safely overexpose film 2 stops and still have plenty of highlights latitude which isn't the case here. :)
But yes, skin looks a bit better with the modified Cine4 above.
 
Yes, but well exposed and slightly overexposed skin looks significantly better than underexposed/shady skin in slog2 anyways, so that's not that much of an advantage. I am mostly looking for decent looking skin in shadows though; in good light and at +1 I can probably live with s-log2. Unfortunately chins, noses and eye sockets occasionally throw shadows. ;)
Don't expect wonders from the flattened Cine4. It may use all the coding space, and it may have somewhat steeper mids, but it is still 8-bit 4:2:0 compressed. Downscaling from 4k should be better; all my tests are with the in-camera codec.
 
i've admittedly only used cine4 once with less than stellar results (but once isn't enough to determine anything), and ive since really just based my whole workflow around slog2, with i'd argue... pretty good results. maybe i'll put some time in to testing some scenarios in 4k with slog2 and cine4.
 
Picture style turned off and portrait style with everything turned down to -3 also seems to be an option. 10bit would make all this unneccerary............
 
Outputting to an Odyssey at 8bit 422 and I don't get any issues with banding on skies and flatly lit walls.
YMMV, but it's been consistent for me.
 
* About the shot from last page, with the highlight and the face in the shadow: yes, Cine4 would make that face look a lot better, but the highlight would look a lot worse (it clips to white two or three stops sooner than slog2, and gets extra space in the shadows). In total, I measured cine4 to have one stop less DR than slog2 (macgregor measured them to be identical, we are probably using a different definition of what's "usable").

* About the OP: I have never had any issues with banding with my a7S+slog2, but I haven't been looking for them either. In any case, I don't overexpose that much, precisely because the highlight rolloff is pretty bad: before going white, colors become ultra-saturated and show extreme banding. Test different levels of exposure and choose the one you prefer. I routinely overexpose by one stop, but always keeping the histogram at hand to see if a lower exposure is needed.

I shot this on the a7S+slog2 (internal), with a lot of saturation in camera and adding a lot more of it in post, and I believe the sky looks wonderful. I didn't do any debanding, and I didn't add grain. I did add some denoiser for the trickiest shots (where I underexposed a lot on the talent to keep alive a much brighter background).
https://www.youtube.com/watch?v=Lb7PH0Ayvp0&index=5&list=PLXfQ_R9rAMS5K0qx8OOqpL-n_uRULcjB5
 
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DPStewart said:
Except of course for the 4 Blackmagic camera models that are under $2500 and all do 10-bit ProRes HQ as well as RAW. :Drogar-Shock(DBG):
Click to expand...

I should have known someone would make me regret being more specific. Is it really 4 models now? Pocket, cinema 2.5k... which other new is sub 2500? I should have qualified my response better, yes. In Sony dslr/mirrorless world, it won't be for some time. In fact I doubt we see it from any major company for a couple years (not counting gh4 as it requires external recorder).
 
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