PixInsight Forum (historical)

PixInsight => Tutorials and Processing Examples => Topic started by: Astrochoup on 2017 September 19 23:17:52

Title: Pixel rejection on a star trail image
Post by: Astrochoup on 2017 September 19 23:17:52

Hi Guys,
My name is Claude - living in France, an this is my 1st topic on the forum.
I'm a relative newbie in astrophotography and Pixinsight user (1 year approx). I'm using a Newtonian 200/1000 on a HEQ5 mount, with a EOS 1000D and 70D most of the time. No autoguiding for the moment.
If you want to see some of my work : https://www.flickr.com/photos/astrochoup/ (https://www.flickr.com/photos/astrochoup/)

A few days ago, i've done some pictures to make a star trail.

(https://farm5.staticflickr.com/4345/36526756233_c1fac0b657_z_d.jpg)
Processed with Pix for integration of the 450+ images, with a Maximum Combination (no pixel rejection). I've tried some pixel rejection to eliminate plane trails  but (i guess as images are not aligned) planes trails are rejected, but also most of the stars !  :surprised:


Is there any trick/tip with Pixinsight to process with such a picture like this ? Using Eraser pixel by pixel, ok, but t'ils a little bit boring and time consuming !  ;) ;)
Thanks for your replies !

Title: Re: Pixel rejection on a star trail image
Post by: mmirot on 2017 September 23 08:17:38

You got it. Rejection requires alignment which pretty hard with star trials

Title: Re: Pixel rejection on a star trail image
Post by: Astrochoup on 2017 September 25 02:01:10

Thanks mmirot for the answer.
So no really tips for this kind of treatment.  :-[

Thanks again,
Claude

Title: Re: Pixel rejection on a star trail image
Post by: georg.viehoever on 2017 September 25 03:32:24

If your sequence of images is dense enough, neighboring shots of stars may share enough pixels such that a very weak pixel rejection may preserve stars, but not airplane trails. Try something like rejection of 0.01% of all pixels.

If your stars dont share pixels on neighboring images, the classical pixel rejection algorithms cannot distinguish between airplanes and stars. We would need something that rejects straight lines, but not circles. That unfortunately does not exist in PI.

Georg

Title: Re: Pixel rejection on a star trail image
Post by: oldwexi on 2017 September 25 08:40:25

Hi Astrochoup!
Would not do a manual (clonestamp) pixelmanipulation of the plane trails.

select a single image with plane trails
align  the previous or following image to this image. rename it to notrailimage.
Generate a blacke line or black rectangle with PixelMath over the trail in the image with the trail.

than execute a PixelMath expression:

iif(trailimage==0,notrailimage,$T) or   iif($T==0,notrailimage,$T)

This replaces the trail area with correct data.
So if you have 5 images with trails its not such a big deal.

Gerald

Title: Re: Pixel rejection on a star trail image
Post by: Astrochoup on 2017 September 27 01:05:19

Thanks Georg and Gerald for the tricks,

Georg : I've done some differents tries,  but i've never used rejection values to obtain a 0.01% rejection (very low)

Gerald : I'm not a PixelMath guru (but I understand the expression), the process sounds good too !

I'll try both of them.
Thanks again

Claude