FS7: Compression Artifacts in Gradients

What LUT are you referring to? LUTs can have an exposure compensation (-1) built into them... but I didn't use a LUT in that screen grab of Resolve that I posted. I simply added a curve.
If you used a Sony LUT in the viewfinder - and had the camera set to 1000EI, then this would have had you open up another stop.

Add some blur to the background will get you out of jail too.
 
egproductions said:
Your going to hate me for this answer but I throw up color bars and do a rough brightness calibration of the monitor under current lighting conditions. I then pretty much judge exposure by eye. I'm almost always within 1/4 stop of my expsoure using this method. In this case, All I had to do was throw on the sony Slog3 lut and my exposure was good right off that bat (all I did was make adjustments to saturation, a little contrast and crushing the blacks a little.)
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I don't hate you at all, in fact I often expose by using a modified 709A Out and setting my exposure from there though I use a waveform at that point. I'll probably be criticized for that.

But I still don't understand what you did. Are you talking about your initial camera exposure or post?
I'm asking about the original slog in camera exposure but then you wouldn't have access to to sat , contrast or Blacks so i don't get the answer. Also which Sony Slog3 LUT as there are a bunch of them.

lenny
 
If you look at the gamma curve for Slog3 it sort of rolls up steeper and steeper until around 25IRE where it keeps going. What that means is that the curve is more compressed at the bottom ie less luminance levels per stop.
When I looked at the DPX the grey background was somewhere between 30-42IRE which to me seems to suggest that exposing hotter would not have helped with the banding. Maybe to some extent it would have helped with noise but I had no problem with noise in the background. As I said, looks like normal banding. The exposure looks good to me, on a low DR scene like this Im not sure if it matters so much as long as your in the upper (less compressed) part of the curve.

I have seen this banding in some of my 4K material on white walls etc but its usually very minor. Im thinking about testing this in a studio (if I have the time) to see if exposure, codec (prores?), resolution has an effect on this.
 
markfpv said:
What LUT are you referring to? LUTs can have an exposure compensation (-1) built into them... but I didn't use a LUT in that screen grab of Resolve that I posted. I simply added a curve.
If you used a Sony LUT in the viewfinder - and had the camera set to 1000EI, then this would have had you open up another stop.

Add some blur to the background will get you out of jail too.
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I meant the lut I applied in post was the Sony LC-709. I applied it and the footage looked great right away (except for the problem at hand). In camera I used the 709 preview lut and since I was rated at 1000 EI I figured I was overexposing by 1 stop. Wit that in mind, does the sont LC-709 have a -1 compensation built into it? I figured it does based on not needed to adjust anything.

I set the expsoure by eye (using the calibrated monitor) on set.
 
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SamEd said:
I would like to know how the DPX was made. It's from Adobe Premiere? I have a feeling the false contouring might have been baked in at that stage.
As a VFX artist I've often had to fix things like this. The BG is very blur-able. Adding some grain will dither it to the display better on 8 bit displays.
If you're in trouble with your clients over this let me know and I can try to help you out. I hope it's not hours of footage...
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Thank you for those that are concerned about getting into trouble or needing a quick fix. My client doesn't know the difference, this is really just something that has been bothering me. I already know a few methods for fixing it in post, however, I haven't even bothered since it's not worth my time in most cases.
 
moldcad said:
Guys - no scopes needed. This is exactly what I'm getting, too - but somehow when I posted my findings, everyone denied anything abnormal :/...

And I don't buy the explanation that the codec is "optimized for fine details, and gets lost in large, flat, semi-monochromatic areas" - just like the OP, I'm getting severe macroblocking in the sky - true - but not clear sky... Some objects must be present to initiate this artefacting; usually clouds, sometimes a tree's contrasty silhouette against the sky.

I'm not bashing the FS7 - great camera - but we really need XAVC-480 !!! Please, Sony :)
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Scopes allow us to see what's going on. In this case it appears there is a healthy negative to work with, so now we begin investigating the workflow.
One step at a time, moldcad.
 
Was it asked whether the OP had noise reduction on ? There's a post on FS7 Sony community forum where someone tested Slog3 XAVC-I and found he had banding when using NR and none with it off. I seem to remember Alister Chapman warning of this also in Slog.
 
It's worth checking out but i'm not convinced that it is defintly the issue since i feel like i had this issue in the past before noise reduction firmware update was available. I could be wrong though. The NR was on high.

Even though I grade slog footage, throwing on a lumetri effect is a lot less GPU intensive than NR in post. I rarley have the patience to wait for NR to encode.
 
Quoted from http://www.xdcam-user.com/2015/10/if-shooting-in-low-light-dont-use-log/

"This is when it’s time to abandon log and go back to a conventional gamma curve. You don’t need log when the scene only has a limited dynamic range. If you use Rec-709, which has a 6 stop range (without any knee) instead of log, at the same ISO, then now instead of recording using only 35% of the available data you will be using almost 85% of the available data and that’s going to give you much more real picture information to work with in post production. You will get a much better end result by not using log.

If you need a bit more than a 6 stop range then there are plenty of other gamma curves to choose from that sit between 709 and log. Gamma curves such as Sony’s cinegammas or hypergammas which have dynamic ranges between 10 and 11 stops.

So remember, when you don’t need a 14 stop recording range, then consider using an alternate gamma curve. It’s not just in low light but also in other controlled lighting situations such as green screen work."
 
Hmm. Having NR on high might have an impact since its such a heavy effect.
If it was on low or medium I don't think (without knowing) it would impact banding.

But I can confirm that I´ve had very similar banding problems in 4K XAVC-I CINE-EI SLOG3 SGAMUT3.CINE with NR turned OFF.
 
Just wanted to followup on this thread. I did some more tests in the same situation as the original shoot. NR off v.s on doesn't make any difference. I rated the camera to around 750 EI. The color blocking in the background is now much better, however, the XVAC is still having trouble with banding with find gradients. This might just be an 8bit/10bit issue v.s codec though.
 
Here's an example when the camera is rated for about 640EI. All is right in the world again:

Here is the DPX file (ungraded) if anyone wants to play around
Shot on the FS7, 640IE, metabones speedbooster, Canon 135 F2 @ f3.5(post speedboosted)
flapjacksample1.jpg


Honestly though, if I wanted the cleanest looking interview, with the best colors and least compression I could just film it using my 5D IV in MJPEG mode. This however, is more than good enough for 99% of the work I do.
 
LennyLevy said:
Was that shotin Slog3 and if so was the LUT in post or applied in camera? just saying 640EI is kinda vague.
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Yes slog3...Lut applied in post. I've been applying luts in post throughout this whole thread. You can check back to see my approach and also the DPX file shows it's in LOG.
 
I honestly couldn't tell you. There is only 1 light source hitting both his face and hand so you would think it would be consistent. Perhaps his hands were just clammy or there was some spill/bounceback from the carpet. He does look more tanned than the other people I interviewed, perhaps he just got back from a vacation? I welcome any guesses.
 
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