Specify reference frame?

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Re: Specify reference frame?

by han.k » 04 Sep 2019, 19:06

The upload to Sourceforge was forgotten. Now it is uploaded. I also cleared default the image edges for the case there is no overlap between the blinked images. ASTAP v0.9.258


Re: Specify reference frame?

by szymon » 04 Sep 2019, 17:27

Awesome, that works perfectly -- thank you!

Re: Specify reference frame?

by szymon » 04 Sep 2019, 16:42

Very, cool, will test ASAP when I get off my work calls. Thanks!

Re: Specify reference frame?

by han.k » 04 Sep 2019, 15:45

Hello Simon,

Okay 2) implemented in version 0.9.257c. I call it a black spot filter. It is implemented at some other places in the program, so it was easy. You can download it now.

I could not read your rar file (damaged ?), but I could reproduce the effect with other files.

Tell me if it works for you.

Best regards, Han

Re: Specify reference frame?

by szymon » 04 Sep 2019, 15:15

Option 2 seems the most sensible to me, but of course I leave it up to you if you can implement such magic :-)

Re: Specify reference frame?

by han.k » 04 Sep 2019, 14:18

Now it is clear to me. By aligning (shift and rotate) the pixels you get pixels positions which are missed. Like trying to spreading 999 pixels in a line over 1000 positions. At one place there will be a hole or a black spot.

In ASTAP if images are stacked, it keeps a record of how many pixels land at a pixel position. The summation is later divided by the number of pixels added. So if you stack 10 images. Some pixels will get the summation of ten values, other 9 and a few 8 due to outliers. That is not a problem as long you keep a record of the number of pixels summed/stacked.

That doesn't happen with the new export. The images are not stacked yet.

There are three options:

1) Calculate on sub-pixel level.
2) Interpolate missing values and fill the black positions.
3) The program you use detects the black spots as outlier and fix the stack.

I assume 3) is not the case, so option 1) & 2) looks like the best options. For 1) I have to spread each pixel in ratio over about 4 pixel positions max. Option 2) is also possible. I assume with option 1) you loose resolution. A single pixel star could will be spread over 4 pixels if there is a 0.5 pixel shift in x and y.....

Re: Specify reference frame?

by han.k » 04 Sep 2019, 13:24

Hello Simon,

I will have a look


Re: Specify reference frame?

by szymon » 04 Sep 2019, 12:44

Hi Han,

So, it seems that this happens every time when exporting the aligned files, and it is reproducible. Here is an example for you to download and try out:

https://www.dropbox.com/s/winq6dsft5nie ... t.rar?dl=1

There are four stacks:

2019-08-27_03-59-10_CLS_19.70_300.00s_1@ 20xFD 20xF 4xD 12xCLS_stacked.fit
2019-08-27_03-51-44_Sii_19.60_300.00s_6@ 20xFD 20xF 4xD 6xSii_stacked.fit
2019-08-27_03-16-37_Ha_19.70_300.00s_12@ 20xFD 20xF 4xD 18xHa_stacked.fit
2019-08-27_01-58-58_Oiii_20.50_300.00s_6@ 20xFD 20xF 4xD 6xOiii_stacked.fit

I have also included the 'aligned' versions of the stacks. Here is how to reproduce the problem:

- Load the four images up into the blink window of the latest ASTAP for windows
- Run the blink once so that it aligns the images
- Look at the images as they blink through -- they are absolutely fine, no black lines
- Then click on "Export Aligned" - at least one of the exported images will have black lines

Every time I try this, with various sets of data, at least one of the files comes out with the black lines. In the example data, it's the CLS filter, which you can see by looking at the files.

Here is a screenshot of the Luminance stack (CLS filter) which has been aligned, but not exported:
cls_aligned.jpg (1.1 MiB) Viewed 5293 times
Here is a screenshot of the same stack after clicking the export aligned button:
cls_aligned_exported.jpg (1.09 MiB) Viewed 5293 times
I hope that helps :-)


Re: Specify reference frame?

by han.k » 01 Sep 2019, 17:44

Meridian flip should do no harm. If it happens again, please report.

Regards, Han

Re: Specify reference frame?

by szymon » 01 Sep 2019, 17:34

Ok, I think that this was due to one of my stacks being 'upside-down'. My Ha stack had a meridian flip in the middle, and while stacking was able to work just fine, it produced a stack that was 180 degrees to the Sii and Oiii stacks. This appears to be what caused the artifacts when aligning the three stacks. When I flipped the Ha stack 180 degrees in gimp and did 'export stacks' again, I got perfect stacks without alignment artifacts.