4 replies to this topic

[Lucian]

I have 10 images of the Trifid in H that I cannot register in PixInsight. They are very typical of nebula images I take all the time except for one thing. They aren't great. There are probably a few reasons for this. The object is between about 20 and 29 degrees above the horizon, and the turbulence was terrible. I also have some mystery tracking/guiding problems I am working through. The PHD logs say 1.77" RMS during the time I took these. So, bad, but I would think they would register. 

 

Images: https://drive.google...101?usp=sharing

 

Essentially, registration doesn't find any stars. And when I tweak the settings in Pixinsight StarAlignment, it can find stars but cannot find any pairs. I've explored many of the settings available. Interestingly, trying to stack in ASIStudio doesn't work either: triangle match failed. 

 

These images were shot in Bin1 with an ASI294mm. When I resample the images to Bin2 size, they register just fine.

 

Is there some typical problem that I am just not seeing? I'm including a link to the original Bin1 images to avoid any issues with bias, darks, and flats. I've tried with and without those with the same results. 

 

Any thoughts? Or are the images just unusable in the original Bin1 size? (I wouldn't normally care to keep these but I'm trying to understand why they won't register.)

 

Example output from the console with all StarAlignment defaults:

* Loading target file: /Volumes/Astro Drive/Trifid Nebula/2024-05-09 H/Light_M20_300.0s_Bin1_294MM_H_gain120_20240510-025219_0001.fit
Reading FITS image: 16-bit integers, 1 channel(s), 8288x5644 pixels: done
76 FITS keywords extracted
Structure map: 
Local maxima map: 
Detecting stars: done
9 stars found.
Minimum star size: 3 px
* Computing global linear transformation.
Matching stars: done
** 0 star pair matches found - need at least 3 matched stars.
* Previous attempt failed - this is try #2
* Reference image: limiting to 8 brightest stars.
* Target image: limiting to 8 brightest stars.
Matching stars: done
** 0 star pair matches found - need at least 3 matched stars.

*** Error: 
*** Error: Unable to find an initial linear transformation.

[Tapio]

I stacked your frames with AstroArt 8 with no problems.

But it's a blurry image with lots of hot pixels. Did you have apply dark frames?

 

And you really should use bin2 with that camera and that focal length.

Even with bin2 and 1654mm focal length your pixel scale is about 0.6" per pixel which is oversampled.

[michael8554]

I downloaded two of your Lights at random and loaded them into DSS.

 

On one only 12 stars were detected at a very low 3% Threshold.

 

And only 6 in the second.

 

So DSS refused to stack as "not enough stars"

[jdupton]

Lucian,

 

I have 10 images of the Trifid in H that I cannot register in PixInsight. They are very typical of nebula images I take all the time except for one thing. They aren't great. There are probably a few reasons for this. The object is between about 20 and 29 degrees above the horizon, and the turbulence was terrible. I also have some mystery tracking/guiding problems I am working through. The PHD logs say 1.77" RMS during the time I took these. So, bad, but I would think they would register. 

   Are you trying to register uncalibrated images?

 

   In looking at the process console log, I see a 16 bit raw FITs file is being input to StarAlignment. Normally, I would expect to see a file name like 

Light_M20_300.0s_Bin1_294MM_H_gain120_20240510-025219_0001_c.xisf

being loaded. The _c at the end is the naming convention PixInsight would use for a calibrated frame. Also, PI would normally save the calibrated result as an XISF file in 32 bit floating point format. Your issue may be from StarAlignment not being able to find the stars in the 16 bit uncalibrated state.

 

   If you have calibration frames for your images, run the image through ImageCalibration using at least a MasterDark frame and see if StarAlignment can pick out the stars following calibration. If you do not have calibration frames, StarAlignment can probably be coaxed into registering the raw FITs frames but you will need to play with the default star detection parameters.

 

 

John

Edited by jdupton, 19 May 2024 - 10:12 AM.

[Lucian]

Sorry for the confusion. First I tried processing with WBPP and a full set of calibration files: bias, darks, and flats. WBPP calibrated the images well but could not register them. So, I went back to the originals and tried registering those originals using StarAlignment thinking maybe something happened to the calibration images, but nothing worked. The images I posted were the originals because I was interested in whether anyone would see an obvious problem with the originals. Maybe I should have posted the calibrated images. But since neither the originals nor the calibrated images will register, I thought the problem was with the originals. 

 

Thanks for looking at these. I know they aren't good images. And maybe they are just not good enough to register them. This may be a multi-year target for me because its so low to the horizon that it will take me ages to get enough quality data. 

 

And yes, I should be shooting these in Bin2. The low angle doesn't allow for Bin1 resolution quality. 

 

I'll turn my efforts to figuring out why the tracking was 1.77" RMS. I suspect it was just a bad night + low angle. 

 

Thanks all