Star cores burned out after sharpen and one other question

Doesn't address the problem but might help with the issue, have you tried turning down highlights? If not in app then in Lightroom or photoshop? I have found that helpful when dealing with overblown stars and course of galaxies

Thanks for your response Greg, highlights in APP even makes the problem worse ... In Photoshop I use it quite often but also have to use an astro action called "less crunchy more fuzzy" in order to get the star profile smooth again, like in this one here:  https://www.astrobin.com/full/339134/O/

However I still have some artifacts left and also sometimes some darker cores in the stars...

It might all be a problem specific to the ASI chip but I have learned often enough that my workflow might be the issue 😉 

Best F

I see. Nice work. Maybe shorter exposures or filter? I'm not familiar with those cameras enough to offer any advice I'm still doing DSLR . Hopefully Mabula will chime in soon.

Posted by: Frank

Hi Mabula, 

Quick question which I wanted to ask since quite a time actually. 

I know that the ASI 1600 is quite prone to burned out stars, however when I compare the sharpening in APP to a normal unsharp mask in Photoshop I see that the star cores are seemingly completely burned out. See the comparison:

I do like the sharpening in APP as especially the galaxy cores show a lot more details, so at the moment I save one tiff sharpened and one tiff without sharpening and put them together in Photoshop with a mask to reveal the details in the galaxies. 

Not sure if this was asked before but I couldn't find a concrete answer using the search. Is there anything I am doing wrong here?

Second question: 

As you can see in the screenshots above, the smaller stars have some strange shapes (with or without sharpen). I remember a discussion here about these artifacts but could also not find it anymore. Can you maybe see from the filename of the stacked image if I have used a wrong rejection algorithm or something?

Here are the registered stacks:

https://www.dropbox.com/sh/lz54dnc1bq6m415/AAAc6fz9kx_l5FYSa_n4bfrga?dl=0

Thanks in advance for your great work Mabula, it is very much appreciated!

Best Frank

 

Hi Frank @foschmitz & Greg @gregwrca,

Yes, first of all, the as1600 is prone to burnt-out stars as is any camera with a 12bit ADC I think. It's a great camera though, I have one myself.

Regarding the sharpening in APP: yes, the sharpening in APP will help greatly in increasing nebulosity and galaxy detail while preserving nice star shapes. The key is to user the Star Protect slider below the sharpen slider as well when you apply sharpening. The default value of 5 % is probably a bit too high. I usually use a value of 2-3 % to protect and sharpen with 5-10 pixels, have you tried that? That should preserve the stars more while still getting nice details in the galaxy cores for instance.

The HL slider can reduce it somewhat as well, but also using less stretching off course.

Stars that are already clipped in the linear data are a problem. And with the asi1600 you will probably have a couple. Then the HL slider doesn't work very well in my own experience.

Finally, a new feauture will come soon to APP called color-preserving stretching (known from arc-sinh stretching), if you apply that on RGB data, then it will prevent burnt out cores very nicely. The stars will keep color in their cores with that technique.

Mabula

Oh ok, great tipp! Thanks a lot Mabula. I always thought the protection was only for the background. Will try it! Happy easter!