Dark Frame causing major artifact

[okiestars (Art Trail)]

Hello everyone!

I am experimenting with my image processing, and have attempted my first image with a dark frame. I am using most of the process outlined in Mike Salway's article from IIS (Thanks Mike!), with the exception of splitting the RGB's because I am not ready to purchase Astra Image for combining them.
What I have accomplished by adding my dark frame is to obliterate my image with what I would describe as a 'heavy weave' artifact (see attached images).
The good image was processed with 1000 bmps, no Dark or Ref frames. The bad image was processed with no Ref frame, but with a dark frame created with Registax from 30 frames of dark video (corrector plate cover installed). I am using a Celestri=on NexImage camera.

Has anyone ever seen this before?

Thanks!

Art

[irwjager (Ivo)]

Hi Art,

Would you be able to post the dark frame itself?
Maybe there's something strange happening there...

Cheers,

Ivo

[Bassnut (Fred)]

Well, for a start, the 1st image is verticaly flipped compared to the 2nd, whys that?.I assume the light and dark had the same orientation?. Looks like the dark wasnt debayered?.

[okiestars (Art Trail)]

I forgot to flip the first image, post processing, is all.
I have attached 2 pics of the dark frame. The first is the processed dark, from 30 frames of an avi. The second is the first frame from that same avi. I tried to process from the single frame, as well, but got a similar result. I believe that there is just too much random, extrinsic noise with this cheaper USB camera for a dark frame to deal with. While I am saving for a better camera, I will try to diminish the noise with a cable shield or toroid. Will post the results for any other NexImage users suffering from noise.

[irwjager (Ivo)]

Originally Posted by okiestars

I forgot to flip the first image, post processing, is all.
I have attached 2 pics of the dark frame. The first is the processed dark, from 30 frames of an avi. The second is the first frame from that same avi. I tried to process from the single frame, as well, but got a similar result. I believe that there is just too much random, extrinsic noise with this cheaper USB camera for a dark frame to deal with. While I am saving for a better camera, I will try to diminish the noise with a cable shield or toroid. Will post the results for any other NexImage users suffering from noise.

Hi Art,

You final dark frame definitely look weird - it's exhibiting the same sort of 'fabric' pattern the corrected image is showing.

How do you create your final dark frame? You're not stacking it by conventional means are you?
To create a dark frame from an AVI, you should average all the frames (stacking typically does not do that by default, though, I think, some stacking programs will let you chose to average all frames).

I will try to diminish the noise with a cable shield or toroid. Will post the results for any other NexImage users suffering from noise.

I'm afraid that's not going to do much; the cable simply transmits digital data (e.g. 1s and 0s). If noise were affecting it, your USB camera would not be recognized to begin with or it would lose connection.
The noise is caused (and digitized) in the camera itself, unfortunately no amount of analog noise supression measures is going to fix that...

Let us know how you get on!

Best,

[okiestars (Art Trail)]

Ivo,

Yes, I did stack dark frame conventionally! I will read up on dark frame creation and try again.

Thanks for the light bulb!

Art

[okiestars (Art Trail)]

Well, I used just one frame of my darkframe AVI converted into a BMP, and used it as a raw darkframe (in Registax) and this eliminated the artifact, as well as the non-random horizontal lines that I have been experiencing. I also decided to throw a $2.99 ferrite core over the cable and this did remove some of the random noise that I would experience from moving the USB cable around. I still have some diagonal lines (random) that occur, but have been exploring the NexImage Yahoo group and found a post that suggested that too much compression may be causing these lines. I will experiment with my exposure and frame rate settings to see if I can alleviate this.

[multiweb (Marc)]

Top of my head this looks like a bayer matrix pattern. My be the dark contained the bayer and the light was debayered or vice-versa.

[mswhin63 (Malcolm)]

I think the dark frame is noise that is variable. So i think this means you will not get a consistent noise spot to subtract.

This is typical noise i find mostly on CCD security cameras some earthing issue or shielding issue.

[mswhin63 (Malcolm)]

Originally Posted by okiestars

Well, I used just one frame of my darkframe AVI converted into a BMP, and used it as a raw darkframe (in Registax) and this eliminated the artifact, as well as the non-random horizontal lines that I have been experiencing. I also decided to throw a $2.99 ferrite core over the cable and this did remove some of the random noise that I would experience from moving the USB cable around. I still have some diagonal lines (random) that occur, but have been exploring the NexImage Yahoo group and found a post that suggested that too much compression may be causing these lines. I will experiment with my exposure and frame rate settings to see if I can alleviate this.

The ferrite core can help depending on where the interference is being picked up. Good luck with that.