Author Topic: alignment method  (Read 699 times)

Offline iagica

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alignment method
« on: 2019 December 08 01:39:29 »
I would like to know the difference between the 2-D Surface Spline and the new Thin Plate Splines which has replaced the first; i am having problem to align image with different scales from 200 to 800 mm (and more...) of focal lenght but i have the feeling that the old method was working better with these type of frames which require distortion correction; have i a bad feeling? can you give me the best parameters to align images with different scales? Thanks.

Carmine

Offline Juan Conejero

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Re: alignment method
« Reply #1 on: 2019 December 08 02:37:04 »
Hi Carmine,

Just the contrary, the new distortion correction algorithm implemented in recent versions of the StarAlignment tool is much more capable and accurate than previous versions. The local distortion correction algorithm aims at achieving centipixel registration accuracy. However, it is also more demanding of good star shapes to perform precise PSF measurements, and this may cause problems under less than ideal focusing conditions.

"2-D surface spline" and "thin plate spline" are more or less equivalent terms to describe the registration device used by StarAlignment when distortion correction is enabled (thin plate splines is used more frequently).

If you upload the images that are giving you problems, I'd be glad to take a look to try to help you.
Juan Conejero
PixInsight Development Team
http://pixinsight.com/

Offline iagica

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Re: alignment method
« Reply #2 on: 2019 December 08 09:06:08 »

Offline iagica

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Re: alignment method
« Reply #3 on: 2019 December 08 09:08:11 »
here the second image....

Offline Juan Conejero

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Re: alignment method
« Reply #4 on: 2019 December 08 10:58:26 »
You have uploaded JPEG images. We can't help you with these. We need the unstretched frames in XISF or FITS format.
Juan Conejero
PixInsight Development Team
http://pixinsight.com/

Offline iagica

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Re: alignment method
« Reply #5 on: 2019 December 09 10:05:33 »
sorry...why? i want to align .tif files and not .fts or .xisf files....

Offline Juan Conejero

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Re: alignment method
« Reply #6 on: 2019 December 09 12:09:30 »
Three important reasons:

- JPEG images have compression artifacts that prevent any useful analysis.

- JPEG images are 8-bit integer images. Severely truncated star profiles are far from ideal to diagnose image registration issues.

- Our image registration algorithms, and very especially our distortion correction algorithms, have been conceived and designed to work with linear data. Anyway, if you really want to work with already stretched data (which is strongly discouraged), please upload the TIFF files in 16-bit integer format at least.
Juan Conejero
PixInsight Development Team
http://pixinsight.com/

Offline iagica

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Re: alignment method
« Reply #7 on: 2019 December 10 09:10:55 »
https://1drv.ms/u/s!ArHSjmg7VTfBh0tPqLYfIQ2wqXva?e=udtscD

this is the link to my onedrive.... the file are too big for your forum.