When in a PI workflow should I remove stars?

[edarter]

Hi,

I'm still using the PI trial (must be time up soon but not going to pay until I have to!) but I'm having a bit of difficulty in understanding when is the best time to separate stars and nebulosity to process separately. I noticed on Starnet 2 that you can remove them at the linear stage, but the starless image produced looks to be non linear. I'm then running in to a bit of an issue getting a good result using DBE and I don't really know if thats related to removing stars (an going non linear) too soon in the workflow.

Any thoughts?

Thanks
Ed

[Ouroboros]

Sorry, I don’t  have an answer, but I think this is a very interesting question.  I look forward to reading the responses. 

Edited July 19, 2022 by Ouroboros

[Budgie1]

I think everyone's workflow may well be different but here's my normal workflow:

1. Crop
2. DBE
3. BackGroundNeutraliation
4. PhotmetricColorCalibration
5. IntegerResample (Bin x2)
6. Stretch with either HistogramTransformation or GeneralisedHyperbolicStretch
7. Starnet 2 or StarXTerminator
8. Curves etc

I do the star removal straight after the stretch so that both stars & background are in the same non-linear state before I start messing with the saturation etc.

Saying this, there's also no reason you can't remove the stars before the stretch because this will allow you to stretch the stars less than the background, so you can control any bloating during the stretch instead of having to do it later or just make the stars less prominent.  

So I guess there's no definite right or wrong answer but I would still do the star removal either right before or straight after the stretch.  

[Lee_P]

9 hours ago, Budgie1 said:

I think everyone's workflow may well be different but here's my normal workflow:

1. Crop
2. DBE
3. BackGroundNeutraliation
4. PhotmetricColorCalibration
5. IntegerResample (Bin x2)
6. Stretch with either HistogramTransformation or GeneralisedHyperbolicStretch
7. Starnet 2 or StarXTerminator
8. Curves etc

I do the star removal straight after the stretch so that both stars & background are in the same non-linear state before I start messing with the saturation etc.

Saying this, there's also no reason you can't remove the stars before the stretch because this will allow you to stretch the stars less than the background, so you can control any bloating during the stretch instead of having to do it later or just make the stars less prominent.  

So I guess there's no definite right or wrong answer but I would still do the star removal either right before or straight after the stretch.  

Same here, I remove stars right after the stretch. 

[tomato]

I remove them after I have a stretched image, but I don’t use PI exclusively to do the processing, I find I get much better background removal results  with APP or Startools than with PI.

[Fegato]

Similarly, I'll do all the non-linear processing, and then stretch (up to a point) and then remove stars. I'll usually do more stretches for contrast after the stars are gone.

For removal I use StarNet2 or StarXterminator. I tend to prefer StarNet2 as I usually prefer the star map it produces (the StarXterminator star map seems a bit washed out for me). But if StarNet2 leaves any artifacts I'm not keen on, often StarXterminator will do a better job (and so I'll remove stars with StarNet2 to get the star map, and then put them back and remove again with StarXterminator). 

[edarter]

Thanks all, really interesting that you all seem to be removing the stars after a stretch. I thought it was the process of stretching that bloated and discoloured stars in the first place and hence trying to remove them as early in the process as possible. I shall follow your well trodden path and see where it takes me

Many thanks!
Ed

[GalaxyGael]

Interesting to see the differences between everyone. I never remove stars but I image from OSC. In that case, most images I see around the place show some signs that stars were reimposed on a processed starless image even my the myriad ways of removing, processing, adding, layering etc.. My eyes seem to be 'sensitive to it' without pixel peeping the image. In other cases it can be done so it looks perfect (in those cases I only know when the workflow stated it, I could not tell from the image).  Narrowband folks like reducing and removing many of them too. Depends I think on the target whether the pre-stretch removal or post-stretch removal is better. APP still provides excellent background removal, or close to as good as it can get, and it does this with stars intact in linear state so avoids blending/overlaying artefacts from some types of images with complex background and stuff behind the stars, and post stretch removal is a little cleaner once the background is flat and sorted. But as a broadband imager for all types of targets I never found a need for star removal during processing.

query though: how many of you do it because it is a workflow process, and have you processed the smae images without a star removal, using masks instead. Any noticeable improvement, worsening, artifact?

[edarter]

1 hour ago, GalaxyGael said:

Interesting to see the differences between everyone. I never remove stars but I image from OSC. In that case, most images I see around the place show some signs that stars were reimposed on a processed starless image even my the myriad ways of removing, processing, adding, layering etc.. My eyes seem to be 'sensitive to it' without pixel peeping the image. In other cases it can be done so it looks perfect (in those cases I only know when the workflow stated it, I could not tell from the image).  Narrowband folks like reducing and removing many of them too. Depends I think on the target whether the pre-stretch removal or post-stretch removal is better. APP still provides excellent background removal, or close to as good as it can get, and it does this with stars intact in linear state so avoids blending/overlaying artefacts from some types of images with complex background and stuff behind the stars, and post stretch removal is a little cleaner once the background is flat and sorted. But as a broadband imager for all types of targets I never found a need for star removal during processing.

query though: how many of you do it because it is a workflow process, and have you processed the smae images without a star removal, using masks instead. Any noticeable improvement, worsening, artifact?

Hi Colm,

TBH I'm doing it because of the target, Western Veil & Pickerings Triangle, which have more stars than you can shake a stick at! To the point I think they detract from the beauty of the Nebula. Having said that, my personal preference isn't to reduce them massively, I'm very much in the camp of keeping things as natural as possible while helping the subject come to the fore. Having said that, there was a fairly recent thread on here (started by Alacante I think) where people were imaging M106 and the different colours in the surrounding stars was truly beautiful, something I wouldn't want to see diminished at all by star reduction!

Ed

[GalaxyGael]

Hi Ed, 

I understand you, and many who like to bring nebulosity to the fore. 

I was curious as to whether anyone did starless processing vs stars in tact processing and saw any specific difference. Maybe some do this as its often stated as a workflow step, without processing with stars at all. Hard to call, when the main aim for an image can be different to a lot of us. Reduction etc is another matter that is more personal I think. 

I'm in the camp where stars are the all there and nebulosity is best supporting actor. This image of Ic1396 I took a while back keeps all the stars, and some NB folk were pleasantly surprised how many and how colourful they can be. But it's par for the course for broadband color imaging conceptually. 

But, their palettes and filters that suppress star intensity show a lot more nebula detail, so there's that. 

[Budgie1]

5 hours ago, GalaxyGael said:

query though: how many of you do it because it is a workflow process, and have you processed the smae images without a star removal, using masks instead. Any noticeable improvement, worsening, artifact?

I use the star removal as part of my workflow, not because it's in my workflow. In fact, with the exception of cropping & stretching, I don't use any process just because it's in my workflow. I may try it and if I don't like what it produces then I'll either leave it out or try something else.

Like you, I'm use OSC only and I used a star mask in the past. I've now found that star removal allows a better view of the background, which is normally my main target. and makes the processing much easier to see what you're doing. I also tend not to do as much processing to the stars, other than saturation and a bit of reduction. So I can do the post-processing on the stars image and then leave it alone while I work on the background. It also allows me to produce other masks for the background, like colour masks, without having to combine them with the star mask.

I don't think there is ever a right or wrong way to do astro processing, it's down to what you know at the time, what you're comfortable with and what produces the results you're happy with. I see it as more of an art form than a scientific representation.