Strange pattern across my footage

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Drew Belanger

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Strange pattern across my footage

PostMon Jul 31, 2017 3:09 am

Hey guys, I was out earlier shooting what I thought was going to be some nice sunset footage, only to find a strange pattern across most of my shots when I got them into DaVinci. I was shooting Raw 3:1, 1600 ISO, 30 fps with a 180 degree shutter on a Canon 12-55 EF-S lens for the bulk of the evening and only found the pattern across those clips. I also noticed the pattern on the view finder while I was shooting but as its a pretty new camera (Ursa Mini Pro) I thought it was just the light hitting the monitor funny.

Based on the picture does anybody have any idea why this happened? Is the lens just garbage? Is this just something that happens when an image gets too dark? Is there a setting I'm missing somewhere? I'd like to know so that I can avoid recreating the conditions that resulted in these shots in the future.
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Gregg Guzman

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Re: Strange pattern across my footage

PostTue Aug 01, 2017 4:09 am

I believe it's just a side effect of how davinci displays the footage. You can pretty much reduce this in davinci by adjusting the settings below. If you export your footage the grid will go away with or without changing these settings.

Project settings > Master Settings > video monitoring: bilinear.

Good luck!
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Dmitry Shijan

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Re: Strange pattern across my footage

PostTue Aug 01, 2017 10:22 am

This is long story. Read this viewtopic.php?f=2&t=51936

Summary:
1. Wrong debayering of second green pixel produces semy-invisible fixed pixel grid which is partially hidden under the sensor noise. As a result at some zoom or scale levels in various players and apps this invisible grid may produce highly visible cross-hatch moire-like pattern.
2. Depending of image contrast, added sharpen and noise reduction amount, and player scaling method this pattern may be visible or not visible at all.
3. In BMMCC which is limited to 1920x1080 resolution this makes sensor Noise and FPN more visible (it behaves like some kind of shadow noise and FPN sharpening, adds additional digital artifacts to noise texture) and this limits the amount of visually usable shadow details.
4. People noticed this effect in BMPCC and BMPC cameras. In BMPCC it is harder to see because it is slightly noisier than BMMCC and pixel pattern more hidden under the noise.
5. This effect depends of camera firmware version.
6. This problem can be fixed with fix in CornerFix app https://sites.google.com/site/cornerfix/using-cornerfix/maze-patterns-1 with applying a BayerGreenSplit500.cpf settings. This fix works only in ACR. All other RAW processing apps ignores it.
7. BM support team answer: "this is currently under investigation by our Development team"
8. BM team RMA few cameras but results are random and not perfect.
9. As a temporary solution for this problem shifting image position by setting X Y position to 0.5 works very well (note that in Resolve this works only with RAW footage, but in Adobe apps it works with both ProRes and RAW footage)
UPDATE: In Resolve, simply use the "pan/tilt" setting in the Color Tab (same values of 0.5 each), instead of "xy position" in the inspector. Should work for ProRes-Footage as well
All my custom made accessories for BMMCC/BMMSC now available here https://lavky.com/radioproektor/
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Drew Belanger

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Re: Strange pattern across my footage

PostFri Aug 04, 2017 10:26 pm

Thanks to both of you guys for your responses, I'm new to the community and it was great to see that people here are so helpful. There have been two different versions of the pattern, one black and one greenish/blue. The black I can get to go away by changing my X and Y to .5 each so thank you to Gregg for that suggestion.

As for the green grid like pattern, I have had no success in combating it. While it is true that it doesn't get delivered with the export is is annoying while trying to edit. Thank you Dmitry for your detailed response, it was much appreciated. I did try to change the pan and tilt values to .5 but that didn't seem to fix the problem. I can live with it as long as it doesn't permanently stain the footage, it's just one of things that you wish you didn't have to deal with. I shot some more footage today stopped down a bit and I can't really see either in the footage so I guess it's just something that is evident at higher ISO's.

Thanks again guys!
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Gregg Guzman

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Re: Strange pattern across my footage

PostSat Aug 05, 2017 4:34 am

Hey man, just want to make sure you saw my suggestion. It had nothing to do with changing your X and Y to .5.

I suggested you change your Video Monitoring setting from Linear to Bilinear.
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Earl R. Thurston

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Re: Strange pattern across my footage

PostSat Aug 05, 2017 3:30 pm

Gregg Guzman wrote:Hey man, just want to make sure you saw my suggestion. It had nothing to do with changing your X and Y to .5. I suggested you change your Video Monitoring setting from Linear to Bilinear.

Indeed, but that won't actually fix the debayering problem he's having. Changing the monitoring setting only hides the moiré side effect in Resolve, whereas adding the 0.5 pixel offset effectively removes the underlying debayering error in the final output.

To quote DEVO, "If you cannot see it, you think it's not there. It doesn't work that way."

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