Halos on a refractor

[Burly]

I seem to get what I call Halos on the larger stars using my refractor , what is the best way to deal with reducing the airiness surrounding the core to make the star look smaller and sharper .
Image 3hrs 240sec subs no filter Nikon D5300 iso200 Tecnosky 70Q quadruplet

[juno16]

Hi Burly,

Please excuse me for jumping in on your post. I have the same unresolved issue and I was hoping that my input might help with a response from the forum.

I have the same halo issue. Not only on the brightest stars, but also on other bright stars. I am pretty sure that the stars are saturated. I cannot offer help because I am also waiting for a reply about the same issue ion this post. viewtopic.php?f=10&t=1669

I just shot another image a few days ago with halos and hope that there is a method in ST to reduce these halos. I am a member of The Sky Searchers Forum and several members there have this issue also.
I am using a similar setup Explore Scientific ED102 with a Nikon D5300 (Ha modded) and an IDAS LPS D1 filter. The image attached is the Monkey's Head Nebula with about 4 hours of 300 second subs.

Seems like I have this issue to some degree in all images.

Thanks,
Jim

[admin]

Hi,

It is quite normal and expected for stellar profiles to taper off in this manner; stars should never look like well defined circles. They are point lights diffracted by the optics and atmosphere, usually yielding a Point Spread Function (PSF) that sees light from the point spread outwards in a tapering-off fashion. How fast the light tapers off and in what fashion, is wholly dependent on the global stretch that was applied.

Meanwhile, the Color module (in Scientific/Constancy mode) will recover RGB ratios and make the coloring (but not the luminance!) appear the same psychovisually regardless of luminance. If you look close-up though, you will see stellar profiles taper off correctly in terms of brightness (luminance) with no discernible halos (I don't see any discontinuities or inflections in the profile, which is what most people mean by "halo").

nohalos.jpg (56.15 KiB) Viewed 6871 times

You can "brute force" modify the stellar profiles using the Shrink module, or use the Decon module to attempt to re-concentrate the light into a point light once again. If the psychovisual hue/saturation retention is not desirable, you can of course reduce the saturation in the highlights or switch to Artistic/Legacy mode. In the latter case, the Color module will mimic the way stretching the color information along with the luminance information destroys and skews hue and saturation values.

In case I am misunderstanding, however, would you be able to post your processing log? Some algorithms can indeed introduce halos in the form of ringing artefacts if over-driven, though this is typically hard(er) to do in StarTools.

Thank you!

[juno16]

Hi Ivo,

Thank you so much for the detailed reply.

My apologies to Burly for jumping in on this post, but as far as I can tell, we are having the same or similar issue.

I just ran through a quick reprocess in Startools similar to the original image that I posted. The processing log is below.


-----------------------------------------------------------
StarTools 1.6.382alpha
Tue Jan 28 20:21:06 2020
-----------------------------------------------------------
File loaded [C:\Users\Jim\Desktop\Astronomy\Assorted Astro FITS and Images\NGC 2174\Monkeys Head nebula NGC 2174.fts].
Image size is 6016 x 4016
---
Type of Data: Linear and was Bayered, but not whitebalanced
--- Auto Develop
Parameter [Ignore Fine Detail <] set to [Off]
Parameter [Outside RoI Influence] set to [15 %]
Parameter [RoI X1] set to [0 pixels]
Parameter [RoI Y1] set to [0 pixels]
Parameter [RoI X2] set to [6016 pixels (-0)]
Parameter [RoI Y2] set to [4016 pixels (-0)]
Parameter [Detector Gamma] set to [1.00]
Parameter [Shadow Linearity] set to [50 %]
--- Bin
Parameter [Scale] set to [(scale/noise reduction 35.38%)/(798.89%)/(+3.00 bits)]
Image size is 2128 x 1420
--- Lens
Parameter [Auto Crop] set to [On]
Parameter [Curvature Red] set to [119.91 %]
Parameter [Curvature Blue] set to [119.91 %]
Parameter [Center X] set to [0 pixels]
Parameter [Center Y] set to [0 pixels]
Parameter [Red Shift X] set to [0.0 pixels]
Parameter [Red Shift Y] set to [0.0 pixels]
Parameter [Blue Shift X] set to [0.0 pixels]
Parameter [Blue Shift Y] set to [0.0 pixels]
Parameter [Curvature Linked] set to [119.91 %]
--- Crop
Parameter [X1] set to [1825 pixels]
Parameter [Y1] set to [22 pixels]
Parameter [X2] set to [26 pixels (-1822)]
Parameter [Y2] set to [1217 pixels (-17)]
Image size is 1801 x 1195
--- Wipe
Parameter [Mode] set to [Correct Color & Brightness]
Parameter [Precision] set to [256 x 256 pixels]
Parameter [Dark Anomaly Filter] set to [5 pixels]
Parameter [Drop Off Point] set to [100 %]
Parameter [Corner Aggressiveness] set to [100 %]
Parameter [Aggressiveness] set to [75 %]
--- Auto Develop
Parameter [Ignore Fine Detail <] set to [Off]
Parameter [Outside RoI Influence] set to [15 %]
Parameter [RoI X1] set to [866 pixels]
Parameter [RoI Y1] set to [265 pixels]
Parameter [RoI X2] set to [1067 pixels (-734)]
Parameter [RoI Y2] set to [1093 pixels (-102)]
Parameter [Detector Gamma] set to [1.00]
Parameter [Shadow Linearity] set to [50 %]
Mask used (BASE64 PNG encoded)
--- Deconvolution
Parameter [Image Type] set to [Deep Space]
Parameter [Radius] set to [1.5 pixels]
Parameter [Iterations] set to [6]
Parameter [Regularization] set to [1.00 (optimal noise and detail)]
Parameter [Mask Fuzz] set to [4.0 pixels]
Parameter [Enhanced Deringing] set to [Off]
--- HDR
Parameter [Small Detail Precision] set to [Max]
Parameter [Channels] set to [Brightness Only]
Parameter [Algorithm] set to [Reveal DSO Core]
Parameter [Dark/Bright Response] set to [1.00]
Parameter [Detail Size Range] set to [1000 pixels]
Parameter [Strength] set to [1.2]
--- Color
Parameter [Bias Slider Mode] set to [Sliders Reduce Color Bias]
Parameter [Style] set to [Scientific (Color Constancy)]
Parameter [LRGB Method Emulation] set to [Straight CIELab Luminance Retention]
Parameter [Matrix] set to [Identity (OFF)]
Parameter [Dark Saturation] set to [2.00]
Parameter [Bright Saturation] set to [Full]
Parameter [Saturation Amount] set to [142 %]
Parameter [Blue Bias Reduce] set to [1.11]
Parameter [Green Bias Reduce] set to [1.00]
Parameter [Red Bias Reduce] set to [1.71]
Parameter [Mask Fuzz] set to [1.0 pixels]
Parameter [Cap Green] set to [100 %]
Parameter [Highlight Repair] set to [Off]
--- Life
Parameter [Detail Preservation] set to [Linear Brightness Mask]
Parameter [Compositing Algorithm] set to [Multiply, Gamma Correct]
Parameter [Inherit Brightness, Color] set to [Off]
Parameter [Output Glow Only] set to [No]
Parameter [Airy Disk Sampling] set to [128 x 128 pixels]
Parameter [Airy Disk Radius] set to [8 pixels]
Parameter [Glow Threshold] set to [0 %]
Parameter [Detail Preservation Radius] set to [20.0 pixels]
Parameter [Saturation] set to [100 %]
Parameter [Strength] set to [70 %]
Parameter [Mask Fuzz] set to [1.0 pixels]
--- Wavelet De-Noise
Parameter [Filter Type] set to [Distance Weighted Outlier Rejection]
Parameter [Grain Size] set to [3.0 pixels]
--- Wavelet De-Noise
Parameter [Scale 1] set to [95 %]
Parameter [Scale 2] set to [95 %]
Parameter [Scale 3] set to [95 %]
Parameter [Scale 4] set to [95 %]
Parameter [Scale 5] set to [0 %]
Parameter [Mask Fuzz] set to [1.0 pixels]
Parameter [Scale Correlation] set to [6]
Parameter [Color Detail Loss] set to [12 %]
Parameter [Brightness Detail Loss] set to [12 %]
Parameter [Grain Dispersion] set to [6.0 pixels]
Parameter [Non-linear Response <] set to [Off]
Parameter [Smoothness] set to [65 %]
File saved [C:\Users\Jim\Desktop\Astronomy\Assorted Astro FITS and Images\NGC 2174\Monkeys Head nebula NGC 2174 for Ivo.tiff].


These brighter stars with the blue rings are the "halos" that I was referring to. Please see the attachment.

If you feel that these stellar profiles are normal, than I am okay with it. I am still a "beginner" at AP.
It you feel that I did something in processing that could result in this blue ringing effect of the brighter stars, please point me in the right direction.
I also realize that this effect could be a result of something in my optical train.

Thanks for your help Ivo!

[admin]

There does seem to be a possible over-abundance of blue stars (perhaps you could match some stars against a catalog?), though color balance doesn't seem to far off given all star temperatures are definitely present.
The bright star you circled do not look particularly objectionable to me (e.g. its seems to be accurate representations of the star temperature for that star), however, depending on the settings, the Life and/or HDR modules could accentuate stellar profiles (they should not modify color however). It is still somewhat tricky for me to establish what it is exactly you take issue with, but try leaving out HDR and Life modules and see if that fixes anything.
Also be sure to try the Legacy preset and Bright Saturation parameter in the Color module, to see if that accomplishes the look you are after (e.g if you prefer a less visible representation of the star temperature).

Would you be able to upload the dataset? I wouldn't mind having a look at the veracity of the coloring...

[juno16]

Thanks Ivo,

I will look into reprocessing in the morning. I will also upload the dataset tomorrow. Right now, it seems that my internet upload speed is very much reduced and the big fits file is chocking the upload down.

Thank you very much for your help with this.

Jim

[admin]

Thanks Ivo,

I will look into reprocessing in the morning. I will also upload the dataset tomorrow. Right now, it seems that my internet upload speed is very much reduced and the big fits file is chocking the upload down.

Thank you very much for your help with this.

Jim

No worries Jim. I had a quick look in the star catalogs (I used the latest version of Stellarium for this) and the few stars I sampled do appear to be roughly correct in terms of how their black body radiation would render in the visual spectrum. The circled bright star, for example, is HIP 29216, which has a perfect B-V index of 0. This translates roughly to a blue-ish A1 class star. The other stars you circled. are a mix of blue and white, with some yellow and orange. Overall it's not too far off (and also depends on your desired white point), but perhaps a slight blue bias reduction is in order.

[juno16]

Hi Ivo,

Thanks a bunch!

Also, thanks for looking up the star color profiles. Its good to know that the star colors and overall color balance are close to realistic. I tried another process not using the Life and HDR modules and did not see any difference in the stars. I also used the Legacy Preset in the color module and it does seem to affect the lessen/reduce the intensity of the color of the star "halo". Interesting. I will tweak that setting more. Thanks.
I really didn't see much difference by different Bright Saturation settings in the Color Module.

Okay, just to make sure I understand. The image and the stars that I am questioning look good. The "halo" that I was asking about is a "normal" effect. I am good with that especially since I see this type of thing in all of my images.

By the way, I recently asked you about building a processing pc on The Sky Searchers forum. Your recommendations were SUPER! This Ryzen 2700x with 32g of ram screams with Startools (and everything else). I can easily process a good fits file in 5 minutes! That compared to 30 minutes to an hour with the previous pc (with a notebook to remember what I did last). Thanks!

I did upload the fits file (~280mb) to Google Drive if you have any reason to look at it. It is at https://drive.google.com/file/d/1vJEsmr ... sp=sharing

Please let me know if I summed this up accurately. I have several folks on the TSS forum that are interested in this information. Are you okay if I share?

Thanks,
Jim

[Burly]

Thanks Ivo explaining PSF obviously different scopes produce different psf there’s me thinking I need tight round balls of light , no problem Jim were all learning .