Repairing Elongated Stars

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STEVE333 United States of America
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Repairing Elongated Stars

#1

Post by STEVE333 »


I just completed a tutorial showing how to repair elongated stars using PixInsight. The repair is intended for elongated stars caused by poor Tracking/Guiding. For this case ALL of the stars in the image have the same elongation in the same direction.

The tutorial can be found at

https://pixinsight.com/forum/index.php? ... ars.18489/

A set of process icons can be downloaded to greatly simplify the task.

Hope it proves helpful.

Steve
Steve King: Light Pollution (Bortle 5)
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Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
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Re: Repairing Elongated Stars

#2

Post by jmfloater »


Nice work Steve. I saw this on PI website and will give it a go.
John

Imaging scope Stellavue SV80S on a Losmandy G11 mount. Roll off roof observatory.
Software: PixInsight, SGPro, Phd2.
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Re: Repairing Elongated Stars

#3

Post by STEVE333 »


Thanks John.

I'll be glad to answer any questions if you have any?

If you would, please let me know how it works for you.

Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
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Re: Repairing Elongated Stars

#4

Post by jmfloater »


My issues are not tracking but axial tilt in most cases, so I'll have to build specialized masks. I will let you know how it goes.

John
John

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Re: Repairing Elongated Stars

#5

Post by STEVE333 »


Thanks John - If you have the GAME script that would simplify your task. A Game mask to define the area you want to correct multiplied times a star_mask should do the trick. Just a thought.

Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
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Re: Repairing Elongated Stars

#6

Post by jmfloater »


You lost me on the multiply by the star mask. The Game mask I have used. Are you sizing the game mask to the star mask using pixel math?
John

Imaging scope Stellavue SV80S on a Losmandy G11 mount. Roll off roof observatory.
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Re: Repairing Elongated Stars

#7

Post by STEVE333 »


Sorry John. Let me try to be more clear.

1) Use GAME to make a mask to define the region where you want to repair stars.
2) Create a star_mask.
3) Open PixelMath and enter the expression shown in the picture below. However, use the name of your GAME-mask and your star-mask. Make sure Create new image is checked. I entered the name "Upper_Right" for the new mask that will be created assuming this mask would be used to repair the stars in the upper-right corner of the image. You can use any name. Once everything is entered just click on the square (Apply) button at the bottom of the PixelMath window. Your new mask with stars only in the area defined by the GAME mask will be created.

EXAMPLE.jpg

I hope this is a better explanation. Please let me know if this still isn't clear.

Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
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Re: Repairing Elongated Stars

#8

Post by jmfloater »


I thought that might be what you were saying I just wanted to be sure I understood.

Thanks!

John
John

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Re: Repairing Elongated Stars

#9

Post by jmfloater »


Steve, I have been using the Game script to produce what appears to be a good mask but when I combine the shifted image to the masked repaired image all stars are effected not just the ones I masked. The area I am trying to correct looks good though. It must be that my mask is not adequate. I will continue to tinker with it.

Quick question: What is the 6.28 multiplier doing in your shift formula?
John

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Re: Repairing Elongated Stars

#10

Post by jmfloater »


I think I have the answer Steve. If doing sections of the image, as in my case, skip the generate star mask step and create the star mask in the Game script only using one of the resampled repair or shift images for star extrapolation. I didn't need to multiply star masks. I will do more tests to confirm this.
John

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Re: Repairing Elongated Stars

#11

Post by STEVE333 »


jmfloater wrote: Tue May 10, 2022 12:13 am I think I have the answer Steve. If doing sections of the image, as in my case, skip the generate star mask step and create the star mask in the Game script only using one of the resampled repair or shift images for star extrapolation. I didn't need to multiply star masks. I will do more tests to confirm this.
If you are talking about the GAME "Star Mask" option don't think this will work John. I created a "Star Mask" using the GAME script. It creates a "Gradient" mask which is bright in the center and linearly decreases in brightness to black at the edges of the mask. The stars are all removed from the mask, so, it has black holes in it where the stars are located. If that's the mask you are talking about, the black holes are right where you want the mask to be white so that star repair can take place.

Maybe I didn't understand what you are going to do?

Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
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Re: Repairing Elongated Stars

#12

Post by jmfloater »


Yes, you are right about the Game script mask Steve. In my case I have elongation in all four corners of the image and I was trying to address each corner separately. When I create a general star mask and then generated a mask with Game and multiply the two, the resulting mask would not protect the stars outside of the Game mask. The Game mask by itself even with all of it's faults produced the best result, though less than ideal. There must be a way to generate a good mask. I'll continue to test it.
John

Imaging scope Stellavue SV80S on a Losmandy G11 mount. Roll off roof observatory.
Software: PixInsight, SGPro, Phd2.
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Re: Repairing Elongated Stars

#13

Post by STEVE333 »


jmfloater wrote: Tue May 10, 2022 1:09 am Yes, you are right about the Game script mask Steve. In my case I have elongation in all four corners of the image and I was trying to address each corner separately. When I create a general star mask and then generated a mask with Game and multiply the two, the resulting mask would not protect the stars outside of the Game mask. The Game mask by itself even with all of it's faults produced the best result, though less than ideal. There must be a way to generate a good mask. I'll continue to test it.

The GAME mask will be white for the region you select (for example, the top right corner) and black everywhere else. When you multiply it times the star mask it will select the stars in the selected region (top right corner) but will be black over the rest of the FOV. I think it will do exactly what you want.

By the way, you will only have to create one star mask. After correcting one corner of the image you can make a new GAME mask for the next corner and then multiply it times the original star mask and it will select the stars in the new corner. This procedure can be repeated as often as desired.

Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
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Re: Repairing Elongated Stars

#14

Post by jmfloater »


Thanks Steve, that was the result I was getting with the mask but the black part of the final mask wasn't masking the remaining stars well enough. The shifting effect modified the entire image. User error I'm sure. Thanks for the explanation. What is the 6.28 multipliers function in your shift expression?
John

Imaging scope Stellavue SV80S on a Losmandy G11 mount. Roll off roof observatory.
Software: PixInsight, SGPro, Phd2.
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Re: Repairing Elongated Stars

#15

Post by STEVE333 »


Yea - When I first tried the technique I didn't use the star mask. As you noticed it modified the entire image and lost some details. That's when I decided to use the star mask so that only the stars were modified.

6.28 = 2 * pi. The trig functions need the angles in radians not degrees.

Good luck.

Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
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Re: Repairing Elongated Stars

#16

Post by jmfloater »


Redoing my star mask and not using default settings. Large-Scale = 4; Smoothness = 5 helped. I also used the brightness mask in Game and selected an area about the size of a quadrant, eliminating the feathering of key areas. May not be the best way but it seems to work.

When I saw the 6.28 I thought you might be converting degrees to radians but wasn't sure. My reference book says to multiply by 0.01745 eliminating the divide by 360 I believe. Many ways to skin a cat so they say.

Thanks for the help Steve, and the useful procedure.

John
John

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Re: Repairing Elongated Stars

#17

Post by STEVE333 »


You're welcome John.

Have fun!

Steve
Steve King: Light Pollution (Bortle 5)
Telescope + Mount + Guiding: W.O. Star71-ii + iOptron CEM40 EC + Orion Magnificent Mini AutoGuider
Camera: ASI 1600MM Pro + EFW Filter Wheel + Chroma 3nm Siii, Ha, Oiii + ZWO LRGB Filters
Software: PHD2; APT; PixInsight ***** My AP website: www.steveking.pictures
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