Strange artefact - help needed!

[almcl]

I have been having a problem with a rather strange artefact on my subs.

While I don't think it's a StarTools issue, I am hoping that someone may be able to suggest a cause and possible ways of using ST to to defeat it.

The attached image is from my Astro modded Canon T5i with CLS clip filter and contains 5 x 180 second subs, 20 flats and 20 offset bias frames, stacked in DSS using average combining and with all other options (as far as possible) set to off. In ST it is binned 35%, auto developed with an ROI on the nebula and wiped with Temp Autodev set to 'yes'. The resulting screen grab is attached. But I have seen this effect on other images on different targets.

screen grab of artefact

SCREEN SHOT4.jpg (371.25 KiB) Viewed 10045 times

Is this the mother and father of amp glows (the image hasn't been cropped) or something else entirely?

And which function in the wipe module would best counter it?

Comments gratefully received.

[Cheman]

First thing I would try is to crop a bit off each edge. You say the image has not been cropped, could be result of stacking artifacts. Worth a try. And/or try increasing the dark anomaly filter
Che

[ChrisLX200]

Yes, definitely stacking artifacts, when you do a stretch after a wipe they cause this result. Do an 'Autostretch' first so you can see the dark edges then crop inside of them (well inside of them). Then you do a stretch again (choose re-do global stretch).

ChrisH

[Rowland]

If it is a stacking artefact, it is in an unfortunate location. How closely aligned were the subs?

[almcl]

The subs don't vary by more than 5 px (in 5184) between any of the five frames and StArt only crops X1 3 px , Y1 1px and Y2 7px.

The bad news is that even when StArt has done its work, then Bin, Autodev and Wipe have finished, the result is just the same. I can avoid it by setting an ROI on the centre of the nebula, but am still not entirely sure that stacking is the root of the problem.

Is Wipe intended for sequential use or , if the first result is unacceptable, is it a case of cancel and use a different alogorithm?

[Cheman]

try cropping manually

You can wipe in any mode, then keep or discard, then another wipe.

Want to link us to your stacked image and let us try?
Che

[almcl]

That would be great, Che, yes please!

here's a link to the stack of 5 lights, 20 flats and 20 bias frames
https://www.dropbox.com/s/g4lh3trge2wtt ... 1.fts?dl=0

The seeing wasn't great so I am not expecting miracles but any improvements or suggestions would be welcome.

[Cheman]

cropped.jpg (326.06 KiB) Viewed 10006 times

All I did was bin, manually crop the image, wipe using defaults,develop, color, stop tracking(denoise)
probably was a stacking artifact.
Now just get more light frames and you will have a very nice image(with more processing of course)

Hope this helps
Che

StarTools 1.4.297
Thu Aug 06 08:31:03 2015
-----------------------------------------------------------
File loaded [C:\Users\Che\Desktop\Autosave001.fts].
---
--- Bin
Parameter [Scale] set to [(scale/noise reduction 35.38%)/(798.89%)/(+3.00 bits)]
--- Crop
Parameter [X1] set to [45 pixels]
Parameter [Y1] set to [47 pixels]
Parameter [X2] set to [1796 pixels (-46)]
Parameter [Y2] set to [1182 pixels (-47)]
--- Wipe
Parameter [Mode] set to [Correct Color & Brightness]
Parameter [UNKNOWN] set to [Yes]
Parameter [Precision] set to [256 x 256 pixels]
Parameter [Dark Anomaly Filter] set to [1 pixels]
Parameter [Drop Off Point] set to [100 %]
Parameter [Corner Aggressiveness] set to [100 %]
Parameter [Aggressiveness] set to [75 %]
--- Develop
Parameter [White Calibration] set to [Use Stars]
Parameter [Gamma] set to [1.00]
Parameter [Skyglow] set to [0 %]
Parameter [Digital Development] set to [81.17 %]
Parameter [Blue Luminance Contrib.] set to [100 %]
Parameter [Green Luminance Contrib.] set to [100 %]
Parameter [Red Luminance Contrib.] set to [100 %]
Parameter [Dark Anomaly Headroom] set to [5 %]
Parameter [Dark Anomaly Filter] set to [Off]
--- Color
Parameter [Cap Green] set to [No]
Parameter [Bias Slider Mode] set to [Sliders Reduce Color Bias]
Parameter [Style] set to [Scientific (Color Constancy)]
Parameter [LRGB Method Emulation] set to [Straight CIELab Luminance Retention]
Parameter [Dark Saturation] set to [2.00]
Parameter [Bright Saturation] set to [Full]
Parameter [Saturation Amount] set to [200 %]
Parameter [Blue Bias Reduce] set to [2.61]
Parameter [Green Bias Reduce] set to [1.57]
Parameter [Red Bias Reduce] set to [2.98]
Parameter [Mask Fuzz] set to [1.0 pixels]
--- Develop
Parameter [White Calibration] set to [Use Stars]
Parameter [Gamma] set to [1.00]
Parameter [Skyglow] set to [0 %]
Parameter [Digital Development] set to [80.43 %]
Parameter [Blue Luminance Contrib.] set to [100 %]
Parameter [Green Luminance Contrib.] set to [100 %]
Parameter [Red Luminance Contrib.] set to [100 %]
Parameter [Dark Anomaly Headroom] set to [5 %]
Parameter [Dark Anomaly Filter] set to [Off]
--- Wavelet De-Noise
Parameter [Scale 1] set to [90 %]
Parameter [Scale 2] set to [90 %]
Parameter [Scale 3] set to [90 %]
Parameter [Scale 4] set to [90 %]
Parameter [Scale 5] set to [0 %]
Parameter [Mask Fuzz] set to [1.0 pixels]
Parameter [Scale Correlation] set to [3]
Parameter [Color Detail Loss] set to [12 %]
Parameter [Brightness Detail Loss] set to [12 %]
Parameter [Grain Size] set to [4.5 pixels]
Parameter [Read Noise Compensation] set to [Off]
Parameter [Smoothness] set to [75 %]
File saved [C:\Users\Che\Desktop\cropped.jpg].

[almcl]

That's brilliant, Che. Many thanks. I'll have a good look at the work flow and, as you say, get some more lights.

[Cheman]

I took a closer look at your image. It looks like you have a bit of a tracking problem (assuming RA is left & right on the image) Each star has a dimmer "companion" just to it's left.
I am thinking it's tracking, not a stacking issue. Were you guiding? did the mount get bumped? Windy? I saw this in some of my early images, and it was a guiding/tracking issue.
If its in Dec, then it might be a backlash issue. Take a look and see if its in each sub frame or only one or some.
Che

Edit: It looks to me like left/right is Dec in this image. I would suspect dec backlash.