Wipe producing strange results

Questions and answers about problems with the software, modules or functionality.

Wipe producing strange results

Postby Jeremy.j » Wed Jul 01, 2020 8:00 pm

Hello,

I am new to this forum and wanted to know if anyone could be of assistance. I am not sure if I am posting in the right section either.

I purchased startools as it looked like a very interesting program but I am having issues when suing the wipe. Whenever I do it on most of the stacked images I get a white block around the image. I have a funny feeling it is the camera at fault as I found on my flats a moving dot. I have attached 2 samples of what happens when I wipe and a sample of the flats with the moving dot. The camera I am using is a ASI 533MC pro. I have cleaned all the glass in line from the sensor to the scope. I have also contacted ZWO about the issue. The problem is I cannot really process further unless I crop out all the white, leaving me with not much to work with.

White ring in startools when wiping
ZWO533 issue 2.png
ZWO533 issue 2.png (476.48 KiB) Viewed 387 times


ZWO533 issue.jpg
ZWO533 issue.jpg (229.69 KiB) Viewed 387 times



example of the flats
Screenshot of multiple flats small.jpg
Screenshot of multiple flats small.jpg (510.21 KiB) Viewed 387 times


Any help would greatly be appreciated.

Jeremy
Jeremy.j
 
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Re: Wipe producing strange results

Postby admin » Thu Jul 02, 2020 10:52 pm

Hi Jeremy,

This behavior bears all the hallmarks of stacking artifacts being present in your dataset. A slight Crop should fix the issue.
You can observe the same sort of behavior explained in the documentation of the Wipe module;

Preparing data for the Wipe module
Image
^ Leaving stacking artifacts in will cause Wipe to interpret the anomalous data as true background, causing it to back off near the location of the artifacts.

It is of the utmost importance that Wipe is given the best artefact-free, linear data you can muster.

Because Wipe tries to find the true (darkest) background level, any pixel reading that is mistakenly darker than the true background in your image (for example due to dead pixels on the CCD, or a dust speck on the sensor) will cause Wipe to acquire wrong readings for the background. When this happens, Wipe can be seen to "back off" around the area where the anomalous data was detected, resulting in localised patches where gradient (or light pollution) remnants remain. These can often look like halos. Often dark anomalous data can be found at the very centre of such a halo or remnant.

Image
^ Halo around a simulated dust speck dark anomaly.

The reason Wipe backs off is that Wipe (as is the case with most modules in StarTools) refuses to clip your data. Instead Wipe allocates the dynamic range that the dark anomaly needs to display its 'features'. Of course, we don't care about the 'features' of an anomaly and would be happy for Wipe to clip the anomaly if it means the rest of the image will look correct.

Image
^ Masking out the dust speck in order to make Wipe ignore that location.

Fortunately, there are various ways to help Wipe avoid anomalous data;
  • A 'Dark anomaly filter' parameter can be set to filter out smaller dark anomalies, such as dead pixels or small clusters of dead pixels, before passing on the image to Wipe for analysis.
  • Larger dark anomalies (such as dust specks on the sensor) can be excluded from analysis by, simply by creating a mask that excludes that particular area (for example by "drawing" a "gap" in the mask using the Lassoo tool in the Mask editor).
  • Stacking artefacts can be cropped using the Crop module.

Image
^ The result of making Wipe ignore the anomalous data. No halo-like remnant is left.

Bright anomalies (such as satellite trails or hot pixels) do not affect Wipe.

I hope this helps. Any trouble, do let us know!
Ivo Jager
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Re: Wipe producing strange results

Postby Jeremy.j » Thu Jul 16, 2020 2:50 am

Good day,

Thank you so much for the informative answer. Excuse the delay in replying. I will try using the mask tool on some of the images I have. I will probably have to go to back to the drawing board with my raw data and re-capture. I am currently in discussion with ZWO as I do not think that it is a piece of dust as it appears to move around the image, especially visible in the flats as per one of the pictures I posted. I am hoping though that it is a bit of dust as that means a simple clean will solve the issue.

Regards
Jeremy
Jeremy.j
 
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Re: Wipe producing strange results

Postby admin » Thu Jul 16, 2020 3:32 am

Excellent - let us know how you go!
Clear skies!
Ivo Jager
StarTools creator and astronomy enthusiast
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