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Bayer-like checkered pattern on mono subs

ZWO ASI1600MM CMOS Monochrome Artifacts Help Needed Troubleshooting
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André Moleiro avatar
André Moleiro avatar

Hi everyone. This started happening about a week ago: I have this checkered, debayer-like pattern all around my subs, even though I’m using the ASI1600MM, which is a monochromatic camera. The pattern is gone if I zoom in or out a little bit. It’s still bad enough to disrupt my workflow, since I like to analyze and select my subs before integration, and also because it’s very annoying needing to change zoom levels at every step of processing.

I have heard the feedback that this might be just an optical illusion, and the pattern is not there. However I didn’t have this issue a couple of days ago, and now I have. So I want to fix it regardless.

I recorded a little video with a demo of the issue, and how it affects my workflow. Any ideas what could be happening? Thanks in advance!

📷 weird_artifacts.jpgweird_artifacts.jpg

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Mikołaj Wadowski avatar
Mikołaj Wadowski avatar

Looks like Moiré patterns to me. I saw similar artifacts when dealing with more noisy subs and that's likely why you're only seeing it in some frames and not others - their SNR is lower.

They shouldn't be visible in the stacked result.

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John Hayes avatar
John Hayes avatar

Something has indeed changed in your camera. The pattern that you are seeing is a moire pattern between the pixels in your display and a high spatial frequency periodic error in your images. That’s why the patten is only visible at certain magnification values. I suspect that if you zoom in to where you can just start to see the pixels in the image, you’ll see a very faint checkerboard-like pattern. In the days of interlaced cameras, this short of error was called an “odd-even” error and if was the result of tiny gain differences in the amplifiers that handled the even and odd rows (and/or columns). I’m not sure why this might be happening in a CMOS camera but it may have to do with the way that the electronics in the camera handles the signal. I don’t know if this will work but you might try to add a small offset of say, 40 ADU, to see if that makes a difference. The problem may be caused by a small change in the bias level so adding an offset might make a difference. If that doesn’t help, you may have to go back to ZWO to see what they have to say.

There are ways to salvage your data. The Canon debanding tool in PI applied to both the columns and rows should fix it. Convolving with a very small kernel should also work but that will also very slightly blur the image. It shouldn’t be very hard to write a Pixel Math expression that would fix it as well.

John

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André Moleiro avatar
André Moleiro avatar

John Hayes · Oct 7, 2025, 03:44 PM

Something has indeed changed in your camera. The pattern that you are seeing is a moire pattern between the pixels in your display and a high spatial frequency periodic error in your images. That’s why the patten is only visible at certain magnification values. I suspect that if you zoom in to where you can just start to see the pixels in the image, you’ll see a very faint checkerboard-like pattern. In the days of interlaced cameras, this short of error was called an “odd-even” error and if was the result of tiny gain differences in the amplifiers that handled the even and odd rows (and/or columns). I’m not sure why this might be happening in a CMOS camera but it may have to do with the way that the electronics in the camera handles the signal. I don’t know if this will work but you might try to add a small offset of say, 40 ADU, to see if that makes a difference. The problem may be caused by a small change in the bias level so adding an offset might make a difference. If that doesn’t help, you may have to go back to ZWO to see what they have to say.

There are ways to salvage your data. The Canon debanding tool in PI applied to both the columns and rows should fix it. Convolving with a very small kernel should also work but that will also very slightly blur the image. It shouldn’t be very hard to write a Pixel Math expression that would fix it as well.

John

This is the most thoughtful and concise response I have seen to this problem anywhere. Now I have a clear course of action. Thank you, John!

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Ani Shastry avatar
Ani Shastry avatar

I had a similar but even more exacerbated issue, which turned out to be an issue with the components on the PCB on which the sensor is mounted on. I sent the camera back to ZWO and they had it fixed and shipped back within a few days. They never identified which specific component was the issue, but replaced the entire PCB and it has been flawless since.

My camera was under warranty so this was rather easy, but reach out to ZWO directly and see what they think.

Ani

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