I bit on the new BM 6K...

scorsesefan

Well-known member
Like the title says I purchased the new BM 6K FF and there's been a handful of problems from the start (fan noise, battery level glitch, lens incompatibility issues) but the most troubling is FPN/banding in the footage. Now to be honest I've been in Sony/slog3 land for a long time, so I may be handling RAW wrong, but I think there's a legit issue with this camera. I've linked to a few braw files I've shot, so any input is appreciated. Thanks

https://go.wetransfer.com/t-C7h7kdhdz3 sunrise. You can see the banding in the lower third of the frame over the wall

bm noise exposure bump copy.jpg

8:1 https://go.wetransfer.com/t-RP3fVYhW2q

Q0 https://go.wetransfer.com/t-TvlX8uCXUq
 
Resolve doesn't see them. I think these files are not supported in my version so my update to 18.6.2 is underway. Then I can open them and read the metadata, see what's going on. Early speculation would be that ISO was raised in lieu of increasing exposure. Exposure methodology can be different than SLog3. Hold the phone, don't panic yet.
 
Using Resolve I see a ton of noise in the shadows and a moving band of Chroma Noise on the roller shutter across the road. NR removes most of the noise but not that chroma band. It also moves a bit like a scan line. You will probably get better insight on this over at the Davinci forum.
 
Using Resolve I see a ton of noise in the shadows and a moving band of Chroma Noise on the roller shutter across the road. NR removes most of the noise but not that chroma band. It also moves a bit like a scan line. You will probably get better insight on this over at the Davinci forum.

It's the chroma band that I'm worried about. The band on the wall, correct? I posted on the Blackmagic Design forum where it's being discussed.
 
I see a vertical rolling chroma band that is most apparant to me on the shutter (garage door?) across the road. It is very noticeable and looks like some scan line artifact.
 
I see a vertical rolling chroma band that is most apparant to me on the shutter (garage door?) across the road. It is very noticeable and looks like some scan line artifact.

Thanks. Need to pixel peep that in resolve.
 
Here is where I see the rolling chroma noise.
 

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This is what I see:

This is how you exposed the BRAW files linked, 400 ISO F9 and used the BMD extended video lut, but when you play it back without the lut you see it in film which amped up the noise. That's not how you exposed for it. The FPN looks more like light smear from the window, but these artifacts are not visible if it was played back the way you shot it. The BRAW looks very clean to my trained eye. You should view it how you shot it. I can't comment on the other still photos because you didn't link to the BRAW files.
 

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This is what I see:

This is how you exposed the BRAW files linked, 400 ISO F9 and used the BMD extended video lut, but when you play it back without the lut you see it in film which amped up the noise. That's not how you exposed for it. The FPN looks more like light smear from the window, but these artifacts are not visible if it was played back the way you shot it. The BRAW looks very clean to my trained eye. You should view it how you shot it. I can't comment on the other still photos because you didn't link to the BRAW files.

Thanks for the input, Tom. I haven't worked with RAW footage in some time, but I don't believe there should be banding when viewing the files without a LUT applied. Were you able to access the first file shot outside? The banding is very evident along the wall in the foreground.
 
I'm getting ready to look at it now. Off the bat, it looks starved for light, shot at 800 ISO and F10. I need a few minutes with it.
 
This is the same thing. Pictured below is how you exposed it for. It's dark. F10. 800 ISO doesn't do you any favors when it just fools you into seeing more light than there is. The iris could have been opened 2-4 stops more open and still not be clipped. You exposed with the BMD Film to Extended video lut, but view it in Film, so it's flat, the darks are boosted, the highlights dimmed, maybe more understandable to say you viewed and exposed the scene in 709 but developed it in log. Imagine if you had the lens iris opened at F2.8- 4.0 what it would have done to the picture I've shown below, clean and natural color. ISO is not your friend in dark scenes, light is. If the 6K has the dual stepped ISO, that's different, there would be a case to be made for setting ISO to the 2nd level because gain is actually added, but with BRAW until that step is reached, changing ISO does not change gain, it just changes the look so that you'll see it differently and expose differently. Higher ISO (in BRAW) is actually about extending latitude into the highlights by causing you stop down because it looks too bright, exactly the opposite of what we need here in the darkness of dawn.

That said, it is NOT to say the artifacts you saw are not there as they assuredly are but you have a choice to not emphasize them by underexposing a scene and pushing it back in post, and that's what's happening. Look as closely as you can at the screen grab below for those artifacts. They are still there, properly buried at the noise floor where they are not objectionable. And if you want the scene tones that coexist in that noise floor range to be seen, open the iris or add more light. You had plenty in reserve, shooting at F10 you were stopped down. You had 2-4 stops unused in the highlights available before you would have even had to worry about clipping in the sky. The potential I see within even these underexposed images is great to me, the noise is low, colors natural, it's clean. There's noise. It exists, and it resides in the floor. You don't want to push into the visible zone.
 

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This is a 500% crop of how you exposed the scene. 500%!! When I watched the scene rolling at 24 fps I could see some moire artifacts in the rollup door, but they looked nicely controlled to me, a definite improvement attributable to the OLPF. But I don't see a banded area, not when shown at the exposure the clip was shot at. Pushed could be a different story but it hasn't jumped out at me. But looking at the scene at 24 fps 1:1 pixel mapped (I can see the whole image because my display is 8K) I do see moire artifacts on the rollup door. You can't get rid of all moire artifacts even with an OLPF.
 

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This is the same thing. Pictured below is how you exposed it for. It's dark. F10. 800 ISO doesn't do you any favors when it just fools you into seeing more light than there is. The iris could have been opened 2-4 stops more open and still not be clipped. You exposed with the BMD Film to Extended video lut, but view it in Film, so it's flat, the darks are boosted, the highlights dimmed, maybe more understandable to say you viewed and exposed the scene in 709 but developed it in log. Imagine if you had the lens iris opened at F2.8- 4.0 what it would have done to the picture I've shown below, clean and natural color. ISO is not your friend in dark scenes, light is. If the 6K has the dual stepped ISO, that's different, there would be a case to be made for setting ISO to the 2nd level because gain is actually added, but with BRAW until that step is reached, changing ISO does not change gain, it just changes the look so that you'll see it differently and expose differently. Higher ISO (in BRAW) is actually about extending latitude into the highlights by causing you stop down because it looks too bright, exactly the opposite of what we need here in the darkness of dawn.

That said, it is NOT to say the artifacts you saw are not there as they assuredly are but you have a choice to not emphasize them by underexposing a scene and pushing it back in post, and that's what's happening. Look as closely as you can at the screen grab below for those artifacts. They are still there, properly buried at the noise floor where they are not objectionable. And if you want the scene tones that coexist in that noise floor range to be seen, open the iris or add more light. You had plenty in reserve, shooting at F10 you were stopped down. You had 2-4 stops unused in the highlights available before you would have even had to worry about clipping in the sky. The potential I see within even these underexposed images is great to me, the noise is low, colors natural, it's clean. There's noise. It exists, and it resides in the floor. You don't want to push into the visible zone.

Thanks for the detailed analysis, Tom. I was exposing for the sunrise, which was pretty bright. I probably had more latitude then I thought. The BM 6K does have a dual base ISO of 400 and 3200... My main concern is the banding. It just shouldn't be there. I get that there will be noise and I'm OK with that. but burying banding under a LUT is not ideal. I have an fx6, too and I know it's apples and oranges comparing the two, but I've never seen any banding at all in slog even under some of the worst scenarios.
 
Apart from the price (and given you have an FX6), can I ask what the appeal of the BM 6K Pro is?
 
Apart from the price (and given you have an FX6), can I ask what the appeal of the BM 6K Pro is?

I actually bought the new 6K FF (the Pro is the prior model). The appeal is the image which is as close as you can get to an Alexa for about 1/10 the price. I figured I'd use it for slower work, but the QC on this camera is comically bad.
 
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