Author Topic: Star size Issue in HA versus OIII  (Read 1665 times)

Offline jerryyyyy

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Star size Issue in HA versus OIII
« on: 2017 March 05 07:59:02 »
I have been processing my data on Thor’s Helmet (30h) and the $%$!! stars in HA are bigger than those in O-III I have tried deconvoluting the HA and not the O-III and various star shrinking tricks.  This is very tricky since there is not a huge difference between the two images.  When you subtract them in PI you will see both the rings generated around stars for having too big HA, but also what I have will become the red edge around the Helmet where there is a bigger HA signal than O-III. 

Maybe this is less of a problem with Astrodon filters than Baaders… $$ upgrade for me. 

Insights appreciated. 
Takahashi 180ED
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Offline aworonow

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Re: Star size Issue in HA versus OIII
« Reply #1 on: 2017 March 05 12:33:55 »
You could try making a star mask in Ha, inverting it, and using the morphological transformation=erosion to shrink the stars.
Alex

Offline msmythers

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Re: Star size Issue in HA versus OIII
« Reply #2 on: 2017 March 05 14:06:51 »
Hi jerryyyyy

Could you upload to dropbox or some other site a linear cropped section of the Ha and O-III images with an offending star?


Mike

Offline jerryyyyy

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Re: Star size Issue in HA versus OIII
« Reply #3 on: 2017 March 05 18:29:43 »
Hi jerryyyyy

Could you upload to dropbox or some other site a linear cropped section of the Ha and O-III images with an offending star?


Mike

Thanks, will send a OneDrive link to you in a PM.  I think you'll see the problem.  These files were drizzled and cropped because of some problems with the horizon.  I'll put the original smaller images in too. 
Takahashi 180ED
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PixInsight Maxim DL 6 CCDComander TheSkyX FocusMax

Offline jerryyyyy

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Re: Star size Issue in HA versus OIII
« Reply #4 on: 2017 March 05 18:33:02 »
You could try making a star mask in Ha, inverting it, and using the morphological transformation=erosion to shrink the stars.
Alex

Thanks, I tried this but perhaps my settings were not perfect.  I sent you a link to the files if you want to take a shot....
Takahashi 180ED
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SBIG STT-8300M and Nikon D800
PixInsight Maxim DL 6 CCDComander TheSkyX FocusMax

Offline msmythers

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Re: Star size Issue in HA versus OIII
« Reply #5 on: 2017 March 05 18:40:42 »
jerryyyyy

Thanks. I'll see what I can do.


Mike

Offline msmythers

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Re: Star size Issue in HA versus OIII
« Reply #6 on: 2017 March 05 19:51:17 »
jerryyyyy

I did a quick look at a crop of your image. This is real basic stuff. Linear fit the images. Make a star mask from the linear Ha image and reduce the levels of the Ha stars using PixelMath by  a very small amount. Of course whatever amount is really needed can be used but all done to the linear image Ha. This is how I would attach this as I think it would have the least impact or artifacts on the image.

Here is a link to a video showing what I did. There is no audio but I think you can follow along. By the way if the video is fuzzy just pause it and restart.
https://drive.google.com/file/d/0B13r3kYqTf8NRzItODJaNDdzQkE/view?usp=sharing

This is going to be a very nice image when your done!


Mike

Offline pfile

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Re: Star size Issue in HA versus OIII
« Reply #7 on: 2017 March 05 20:30:22 »
i feel like part of the problem is that the images are slightly out of focus... this may have exacerbated the star sizes.

rob