stacked image artifact

David O'Hara

for the last couple months, when I've stacked my images, I've been getting this horizontal banding pattern in my images (see attached). I tried taking new darks earlier this month, and have used flats/dark flats for the integrated image. Any idea why this is happening? It's been almost impossible to eliminate it in post-processing without severely impacting the detail, dimmer features, and contrast of the image. 

Thank you,

Dave

BlockHead

Oooh... not good.

This looks electrical.

FIrst thing to do do is eliminate any variables. You should attach your USB cable (or whatever it is) directly to the camera and take some images. Do not run through the mount or near any other devices. 

If you still have the issue... change cables.

If you still have the issue... call camera manufacturer. 

This is what I would likely do. 

-the Blockhead

David O'Hara

okay sounds good! At some point I started powering the camera through my mount so hopefully that's the issue. usually I plan all my acquisition through the ASIair. Is that something you would avoid with this test? I'll do this test on the next clear night and take it from there. Thanks, as always for your help!

Dave

David O'Hara

I have a little update: I swapped my cables and plugged directly into my camera while imaging. took my subs and things looked good- no banding pattern visible. I stacked everything with darks, flats, dark flats and the banding pattern came back. I thought this was weird, but thought maybe whatever noise was actually in the subs was amplified when stacked, so tried stacking my lights without calibration frames and the banding wasn't there. lights stacked with darks, no banding. lights stacked with flats, no banding. It only seems to appear when im calibrating with both my darks and my flats. I take my flats with the spike-a flat panel so when I turn up the brightness and shorten exposure time of the flat, the banding noise seems to improve, but only to a certain extent. With all this in mind, is there something else that might be going on, or is it possible the calibration frames just "bring out" the inherent electrical issue? I've attached a few stacked images to show the differences. Thanks again,

Dave

BlockHead

David,

The issue in the last frame shown here is not the same as what you started with. The last frame has walking noise because you did not dither your exposures. I would put money on it. :)

Also, your point concerning not seeing the issue when *not* calibrating images is a misunderstanding. 

The brighter (uncalibrated) images have an extra signal that just overwhelms the faint noise you are looking for. I go to great lengths to demonstrate this in my useful pixel math video:

https://www.adamblockstudios.com/articles/useful-pixel-math-another-introduction

Please review it... I would enjoy knowing if my demonstration makes sense with respect to my answer here. 

So from my point of view- you did solve one problem based on your images (no horizontal banding) and now have a much more common issue of dithering. Am I correct on this point?

-the Blockhead

David O'Hara

you're spot on! no dithering haha

your video was also very helpful in understanding why the image looked "worse" after calibrating. I actually had wondered the same thing in the past about DBE. 

I'll try dithering on the next clear night and see how things turn out! Hoping for a clear night before the spring 

:))

Thanks again!

Dave