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Canon 600D walking noise


Elp

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Anyone know a good way of removing the following walking noise with a Canon 600D?

Image below was taken with an L-extreme filter out front (shouldn't make a difference), ISO 1600, 60s each, an hours data with all calibration files applied (dark, flat, dark flat, bias), I've also stacked without the darks and it's the same, stacked in DSS using Kappa Sigma 2_5. Imaging run had dithering applied 10 pixels every 10 frames.

I've never really had a good run with this camera due to this noise pattern, sometimes it looks more severe like thick pixel black rain has flooded the image.

 

194112149_Canon600Dwalkingnoise.thumb.jpg.bafff60fb8fcf0d74d8e2ad27a38c507.jpg

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I would say dither, but you already do that. Perhaps the amount and frequency of your dithers are not enough? Judging from the fact that there still is clear walking noise points to your current dithers being insufficient. 1 dither for every 10 minutes sounds a bit optimistic, maybe half that to no more than 5 minutes per dither but preferably maybe 3 minutes per dither.

For processing later if for some reason going back and shooting more is not possible (like this time of year) i dont know of any foolproof method. Attempting to denoise the pattern away turns the image into a painting, but desaturating the background could work OK. The pattern on my 550D is somewhat biased towards purple so selecting that colour in PS and desaturating can improve the image. Then select background and desaturate and it could salvage the mess, but if it was really bad its not going away.

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I'll try and increase the dither frequency, it's a bit of a pain due to using a dual camera setup but I find the dither doesn't really affect the camera which is imaging at the time of the dither. Hopefully tonight will be clear.

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I agree that the dithering frequency needs to increase. Every 10 frames is only 6 times in the hour which will not be enough to 'staitstically' remove the noise. You could adjust the clipping algorithm but you will probably start loosing detail.

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Hi

600d, so no dark frames of any description. Instead simply use a master bias or even easier -and just as effective - subtract a constant bias  value per pixel. For the 600d, 2048.

Don't forget to stack using a modern clipping algorithm -available in Siril- and take more frames of longer exposure.

+1 for the suggestions to dither.

Cheers and HTH

Edited by alacant
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3 hours ago, Elp said:

I'll try and increase the dither frequency, it's a bit of a pain due to using a dual camera setup but I find the dither doesn't really affect the camera which is imaging at the time of the dither. Hopefully tonight will be clear.

I'm not a DSLR imager but Tony Hallas suggests a minimum of 12 pixels for dither. If your dither really is happening it must affect the second scope. If you see no loss of resolution on the scope imaging during the dither then I suspect the dither can't be happening. Software can lie!

Olly

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Before I mess around with the latest data, I used the existing data and I followed the bias pre process screenshot within this thread from 19 June by @alacant:

 

However after completing the pre-process I get the following which is not right as the flat hasn't been applied correctly:

836286671_Sirilafterpreprocess.thumb.jpg.8bbfbe683107d15bfc62ec4b0bbe11c2.jpg

 

These are the pre process settings I used:

1868585990_Sirilpreprocesssettings.thumb.jpg.ab24e2fce127a9061e20323c5095b431.jpg

 

And this is the master flat used in the above settings (uploaded here as a JPG for reference to save on file size):

copy_Siril_FlatsStack_stacked.thumb.jpg.f000637e3d7ca64c8450c06a51972cce.jpg

 

So what's going on here?

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Btw, tried dithering 30 pixels every 5, seems to have helped a lot even with all calibration files (darks, flats, dark flats, bias) applied.

Due to the simple dual setup however I did lose around 40 minutes of subs due to the dithering.

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@alacant, I tried the above but the overblown flat problem still exists, I'd say it's actually brighter than before. I might abandon this data as the larger distance dither and increased frequency produced cleaner results.

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14 hours ago, Elp said:

below.

The flat frames are (way) over done. You're around 30000. Even un-stretched you can see detail therein.

On a 600d, aim for a value of no more than 2000. On an eos, Av will give you a good approximation to this; aim for an exposure of at least 2s.

For reference, I've included a flat frame from one of our 700ds with the exposure determined via Av.

HTH

ss_2.thumb.png.1032ff13416a518f8d507d9ea34140c5.png

 

ss_4.thumb.png.3ded4ffb6ff4d5eaf998eaf023cc7b8e.png

ss_5.thumb.png.0c249e992c06e3bd66f65a6bd63f7b38.png

 

Edited by alacant
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Thanks for taking a look, I'll have a look at that next time. It's odd though as I used the auto flat exposure setting in the asiair, I also did this on run 2 and 3 and 2 and 3 are fine. Run 1 is also applied fine if no pre processing is carried out on the flat prior to stacking.

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5 hours ago, Elp said:

Run 1 is also applied fine if no pre processing is carried out on the flat prior to stacking.

Assuming I have 'Run 1', not here it doesn't:

ss_7.thumb.png.aed1cf1358872258734d8a65db9aa70c.png

I think maybe the frames you posted had already been processed.

Cheers 

Edited by alacant
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If stacked with all calibration frames (flat, dark flat, bias and darks) I get this from DSS and displayed via histogram stretch view in Siril, I didn't provide you with all the master calibration files:

602729661_DSSstackedallcalibrationframesapplied-Sirilviewerhistogramstretch.thumb.jpg.e500e00f1a4d70ef25a42af00d6f1c48.jpg

I can still work with this after doing a background extraction. Also using a small dust and scratches application in PS reduces some of the streaks, I also have 4 hours total from run 2 and 3 to apply to this so will post it up once done.

Next time using this camera I'll have to take some flats via AV mode. Thanks for your help.

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Not sure if it will help the walking noise particularly but I think the recommended ISO for the 600D (I use this camera as well) is 800. I did also find that when I used DSS for stacking it was horrible for horizontal banding, switched to APP and the problem disappeared. Again, may or may not help with what you are seeing, but thought I would share as its the same camera being used.

Thanks
Ed

Edited by edarter
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