FS7: Severe Banding in S&Q mode 180FPS

[benjaminreece]

Guys,

Maybe this is an issue that has been discussed, if so point me in the right direction.

Over last weekend I shot for a bit in Henderson Beach, FL. CINE EI, 1080FPS

While the footage was in flat preview, I could not see any banding, but as soon as I dropped the Impulz Slog3 FujiColor 200_FC (VS, & FPE it also shows up) LUT on it, I'm seeing major banding in the sky.

Check out the 1080P version, you can clearly see it on the opening shot (as well as others) .

UPDATE #1, I've found the root of the issue is that the S&Q XAVC is much much more brittle than the 4K 10Bit XAVC- this video has been updated with a more subtle LUT from Filmconvert. Basically I had to dial back the curve and color settings so as not to crush the codec. This is a big reason why you might look at this camera as a 60P camera, with 180 only for specialty applications (unless recording RAW out

UPDATE #2, Ok, I may be totally wrong- playing around with this in Resolve and I'm seeing no banding issues and I'm pushing and pulling all over the place. Stay tuned.

UPDATE #3, Definitely seems to be an issue with premiere and secondary corrections as simple as a Luma curve. When I apply a luma curve and a LUT I easily trip into massive banding. With just a lut and no secondary corrections, its much better but you can see the banding. With resolve, I can do multiple curve adjustments, secondary and tertiary and not run into banding with LUT on or off. So, for now, seems I'm going to have to round-trip color to Resolve unless someone can help me figure this out in Premiere.

The video was exposed well, and from what I understood the color should be 10bit XAVC, a world class codec, so not understanding why I'm seeing banding? What good is a log codec when I go to pull in that information via LUT or Luma curve and the XAVC codec choose to over compress the sky?



Below is the raw footage exported with no correction in 1080 ProRes HQ so you can duplicate the problem yourself if you wish.

https://vimeo.com/128514697/download?t=1432232485&v=370335738&

(1.48GB)

Is there something I'm doing wrong or is there a workaround?

 

[FrameFarmMedia]

I think the impulz luts are the issue. Does it still band with the Sony official luts?

 

[benjaminreece]

I think the impulz luts are the issue. Does it still band with the Sony official luts?

I stand corrected. I think you are right, it is the LUTs I think. When using a simple LUMA curve + fast color corrector I can get alot farther with much much less banding.

Do the FilmCovert luts have this same issue?

Thanks!

 

[Ben Scott]

Not had filmconvert introduce any additional banding

 

[benjaminreece]

Ok, so it actually does seem to be the codec- when I pull the exposure down 2 stops with fast color corrector (to compensate the exposure on this shot which was higher than the others)....

I get major banding. Again, the sky was not clipped, its there, just in the "highlights".

Is this just a limitation of the codec? If this were Redcode, I would expect to see beautiful highlights coming back into play as I pulled the exposure/luma curve down

Here is a closer look:

 

[Ben Scott]

It most certainly is not redcode

 

[benjaminreece]

Another example of banding, this time with FILMCONVERT for FS7

No LUT/untouched

W/ Filmconvert LUT, nothing else touched.

The Settings:

 

[benjaminreece]

It most certainly is not redcode

Nope. Its XAVC, a mostly un-charted country, so let me know if you've seen this issue before, have some thoughts, or if you just know this is not REDCODE.


It seems that the LUTs programmed into Filmconvert/Impulz are tuned to max out the range out of the 10bit XAVC, but when you pull down a LUMA curve, or adjust exposure before the LUTs or after, you run the risk of clipping out color information.

So, it seems if one wants to use LUTs, you have to be careful. I'm thinking for simple projects/fast turn around, the LUMA curve + other premiere native coloring tools are probably my preferred as the color matrix on CineEI mode looks great to my eye and I won't run into these nasty clipping issues.

Curious if anyone has any other insight.

Thanks!

 

[benjaminreece]

Ok, I've definitely narrowed it down to being an issue with the latest version of premiere CC. Be warned, you get to pull your image around ALOT more in davinci then premiere, for what reason, I'm not sure yet.

Anyone have any ideas? Definitely something to do with their lumetri processing engine.....

 

[Liam Hall]

I'm not seeing banding with Lumetri. What do you have your render and playback settings set to?

 

[benjaminreece]

I'm not seeing banding with Lumetri. What do you have your render and playback settings set to?

Here. All that's on this clip is a Impulz FujiColor 200 LUT & a Luma curve (slight). In premiere, banding, in resolve, none. Same settings.

Notice that clip? It has a slight luma curve bringing in the highlights on the clip itself, then a lut on top of it.

Thats what I get, all that banding.. When I turn off the luma curve, the banding smoothes big time but is still there slightly. Where as in resolve I can pull the Luma curve all around and use the LUT.

So, in summary guys, the LUTs are not the problem, I can use in Resolve fine, and it looks great. (as you can see in the updated video above)

 

[Nate Weaver]

This would probably be the precision with which Premiere/Lumetri applies the LUT.

LUTs or their application can be limited to 17x17x17, 33x33x33, or 64x64x64. You can give Premiere a 64x64x64 LUT (Impulz LUTs are 64 cubes), and it could be tossing out 2 out of 3 entries in the LUT and interpolating the rest, effectively making it a 17x17x17 LUT. The type of banding this makes looks a little different than 8bit luma banding. It's more like banding between transition from one color to a very close neighbor. In the Impulz LUTs you'll see it from cyan in the shadows to warm midtones, among other transitions.

This would be processing power or code limitation issue. A lot of live-LUT application hardware, such as the Smallhd DP7, and Blackmagic HDLink, to my knowledge, are 17x17x17 because it's less processor intensive. In Premiere's case, they just need to update the Lumetri code, it's old school.

Most of the time, LUTs are not modifying the image so heavily that 17x17x17 becomes an issue.

Impulz has a LOT of color transforms going on in each LUT, and throwing away 2/3rds of the modification it's supposed to be doing and interpolating between the remaining transforms...well, you saw the result. Not good. Ok for preview, not good for final output.

 

[stokstad]

So is Lumetri doing this only for preview or for render output also?

 

[Nate Weaver]

So is Lumetri doing this only for preview or for render output also?

It appears for final output. I said that last thing about "ok for preview" because it's a shortcut some monitors with 3D LUT support are taking, but it's a different story if software is doing it and you learn the hard way.

 

[benjaminreece]

This would probably be the precision with which Premiere/Lumetri applies the LUT.

LUTs or their application can be limited to 17x17x17, 33x33x33, or 64x64x64. You can give Premiere a 64x64x64 LUT (Impulz LUTs are 64 cubes), and it could be tossing out 2 out of 3 entries in the LUT and interpolating the rest, effectively making it a 17x17x17 LUT. The type of banding this makes looks a little different than 8bit luma banding. It's more like banding between transition from one color to a very close neighbor. In the Impulz LUTs you'll see it from cyan in the shadows to warm midtones, among other transitions.

This would be processing power or code limitation issue. A lot of live-LUT application hardware, such as the Smallhd DP7, and Blackmagic HDLink, to my knowledge, are 17x17x17 because it's less processor intensive. In Premiere's case, they just need to update the Lumetri code, it's old school.

Most of the time, LUTs are not modifying the image so heavily that 17x17x17 becomes an issue.

Impulz has a LOT of color transforms going on in each LUT, and throwing away 2/3rds of the modification it's supposed to be doing and interpolating between the remaining transforms...well, you saw the result. Not good. Ok for preview, not good for final output.

Given further research this is still the best explanation I found. So, I'm going with this.

Dont use premiere to grade your footage, even if just straight LUTS/film convert.

I would love to hear what filmconvert reps or premiere support would say of this. Seems to be an issue if they are trying to sell all their new color features in CC.