Agressive vertical stripes?

[timbytheriver]

Been having trouble recently getting rid of vertical stripes (see image). Have tried using the options in MLV App and MLVFS to no avail.



Any ideas how to clean up?

Many thanks!

5D3, same on: a1ex 4K_snd, Danne 4K_snd builds.

[ilia3101]

Looks like fixed pattern noise to me, plus significant underexposure. Try using a darkframe (create one with the same settings, shutterspeed and iso)

[timbytheriver]

@Ilia3101 Thanks. Do I just take a still with the lens cap on? Never used this… (it's an underexposed area of a ETTR shot – with the shadows raised; you just can't see the correct highlights!

[ilia3101]

Yeah just use the lens cap, and be in the dark if possible.

Could take a few pictures and average them too.

Is this in video or photo?

If it's video then take a short dark video instead of a still.

[timbytheriver]

Righto. It's video. Will have a go. Thanks!

[timbytheriver]

[Forum searched] Am I correct in thinking mlv-dump is the only way to tackle dark-frame subtraction on an mlv file?

Think I've found an option in MLV App. 

[ilia3101]

I still haven't ever done dark frame, curious to see how well it works.

[timbytheriver]

@Ilia3101 So far I've followed the instructions 33m in on this useful video for MLV App – but the results haven't been too good so far… will persevere. If anyone knows any important tips – please share!

Cheers!

[Danne]

Could you upload a sample of that file?

[ilia3101]

Was it shot in crop mode? maybe the crop window was in a different place, not sure how to help with that. Please uplpoad a file if possible.

[timbytheriver]

Here's a sample. It's ETTR but the shadows are dark! Not crop mode I think. Took so many tests recently can't remember! 

https://drive.google.com/open?id=1YYuJOJERQVGy_u9xAybg1fkxaFcmBanX

[Danne]

Darkest file of the year . Think it´s a lost cause. Thanks for sharing.

[timbytheriver]

Do I get a prize? 

But seriously. It is intentionally a low-key ratio stress-test. I'd expect uniform noise in the underexposed areas – but the smearing and banding seem odd to me.

I took some night exposures at ISO6400 yesterday. I show grabs of the grade done in MLVApp – and the corresponding frame with Dark Strength at 0. The noise is uniform, and expected – but without any worrying vertical banding or smearing.










I guess I'm just chasing the holy grail of consistency. Any ideas?

Many thanks.

[histor]

Banding is always there. At iso 6400 its simply hidden under aggressive amplifier noise. There was a great experiment to correct it in camera.

From my photo experience banding is partly corrected with bias and dark frames and finally goes away after applying flats.
There are special tools for that like Superbias and Canon Banding Correction scripts in PixInsight.
Video case is a bit more complex as we don’t have optical black areas in the frame.

[timbytheriver]

Thanks @histor for the info. The Superbias page is particularly impressive. That sensor calibration looks like it has great potential – would be awesome to get it working in mlv! Or even in MLVApp! @masc

PS The ticked answer linked is an interesting read about banding noise that confirms @histor's comment. https://photo.stackexchange.com/questions/41874/what-causes-banding-noise-in-cmos-sensors