Stephan’s Quintet - Stephan’s Quintet – HCG 92 / Arp 319 Compact Galaxy Group - Image Processing Walkthrough

Nov 22

Written By Patrick A. Cosgrove

November 23 2025

My image of **Sh2-171 – The Teddy Bear Nebula**

🔭 Project Summary

Target: Stephan’s Quintet – HCG 92 / Arp 319 Compact Galaxy Group

Capture Dates: October 16, 17, 26–28, 2025

Constellation: Pegasus • Distance: ≈ 270–300 million light-years (main group)

Type: Compact Galaxy Group / Interacting Galaxies (with foreground spiral NGC 7320)

Imaging Period: October 16–28, 2025 • Total Integration: 23 h 57 m (LRGB)

Filters: L · R · G · B (ZWO 36 mm LRGB Gen II)

Telescope: Sharpstar SCA260 V2 260 mm f/5.0 Special Cassegrain Astrograph (≈1300 mm)

Camera: ZWO ASI2600MM-Pro (−15 °C; Gain 0 LRGB)

Mount: iOptron CEM70 on custom steel pier

Processing: PixInsight (LRGB) & Photoshop

Location: Whispering Skies Observatory · Honeoye Falls, NY (USA)

Acquisition notes: L: 412 × 90 s; R: 181 × 90 s; G: 174 × 90 s; B: 191 × 90 s at −15 °C, Gain 0; total 23 h 57 m after culling bad subs.

🔗 Detailed Processing Walkthrough →

Table of Contents Show (Click on lines to navigate)

Special Note

Welcome to the New Image Processing Page for this project! You got here by following a link in the main Image Project Report, and you can easily return to that by using the back button on your browser.

Abbreviations Used

BXT BlurXtermminator by RC-Astro

CC Cosmetic Correction

CT Curves Transformation Process

DBE Dynamic Background Extraction Process

ET Exponential Transformation

HT Histogram Transformation

NXT NoiseXterminator by RC-Astro

PI PixInsight

PS Photoshop

SCNR Subtractive Chromatic Noise Reduction Process

SPCC SpectroPhotometric Color Calibration

STF Screen Transfer Function

STF->HT method – Drag the STF triangle to the base of HistogramTransformation, then apply it to the image to take it nonlinear.

SXT StarXTerminator by RC-Astro

WBPP Weighted Batch Preprocessing Script

Processing this Image

(All Processing is done in PixInsight, with some final touches done in Photoshop)

1. Blink

First, I screened the data for thin-cloud frames and obvious defects.

Ha
- 4 frames removed - for thin clouds
O3
- 1 frame removed - for thin clouds. Note - strong gradients and weak signal
S2
- 2 frames removed, for thin clouds. Note - strong gradients and weak signal
Darks
- All looks ok
Dark Flats
- All looks ok
Flats
- all good

2. WBPP 2.8.9

With the bad frames identified, I ran everything through WBPP with a quality-first configuration:

Reset everything
Load all lights
Load all flats
Load all darks
Select - maximum quality
Reference Image - auto - the default
Select the output directory for the WBPP folder
Enable CC for all light frames
Pedestal value - auto
Darks - set exposure tolerance to 0
Lights - set exposure tolerance to 0
Lights - all set except for a linear defect
set for Autocrop
WBPP run 1:29:49 - no errors

3. Load Master Images and Create Color Images

Load all master images and rename them.
Using CombineChannels, create the Master SHO color image

4. Initial Process of Linear SHO data

This workflow corresponds to the SHO processing approach summarized in the main project page.

Run DBE for the SHO linear image. Use subtraction for the correction method. Choose a sampling plan that avoids the nebulae (see below)
Run BXT - correct only. This cleans up the stars at the corners. Not much to do in this image as the scope is very crisp.
Run PFSImage script to measure star sizes. X = 2.65, Y = 2.56. This will influence the values used in BXT.
Run Full BXT - I am using an enhanced set of values to shrink stars more. These are about double the measured star sizes. See the BXT Panel Snapshot below.
Run NXT V3 - refer to the parameters from the snapshot below.
Run SXT and save the SHO stars.

Master SHO Image DBE Sampling Plan (click to enlarge)

Master SHO- Before DBE (click to enlarge)

Background Subtracted by DBE (click to enlarge)

Measuring Star Sizes with PFSImage Script (click to enlarge)

Before BXT (Copy)

BXT Correct Only (Copy)

BXT Full (Copy)

After NXT V3 (Copy)

Master RGB Before BXT Correct Only, After BXT Correct Only, After BXT Full, After NXT

Master SHO Starless Image (click to enlarge)

Master SHO Stars Only Image (click to enlarge)

5. Fix SHO Stars and Go Nonlinear

Use Seti Astro NB to RGB Star Script to fix and take stars nonlinear

Extract the individual S2, Ha, and O3 images with PI’s PSplit Channel Tool.
We do this because the script requires it - it seems unnecessary to me. The script should offer an input that is already an SHO Image.
Run the script. The split-out Green image is the Ha channel, the Blue image is the O3 channel, and the Red image is the S2 channel.
Use the parameters shown below. ( I choose to boost the color a bit and increase the stretch factor)

The resulting star image was reasonable, but with all of the nebulosity going on in this image, I decided to boost the stars and adjust the color with one final CT. I increased the blue curve and reduced the red curve. See the result and the CT curves used below.

The NBtoRGB Stars Script and parameters used.

7. Process the Nonlinear SHO Starless Image

Create the WarmMask
- Use the ColourMask Process with Star Hue 338 and end hue 68, with a blur of 5
- Apply CT to boost the mask
Create the CoolMask
- Use the ColourMask Process with Star Hue 166 and end hue 263, with a blur of 5
- Apply CT to boost the mask
Take the SHO Starless image nonlinear using the STF->HT method
Run NarrowBandNormalization - see parameters used below
The initial color balance has too much magenta in it. To remove this, I am going to use my Invert Trick:
- Invert the Image (magenta is now green!)
- Run SCNR Green at 0.9 (removes the green!)
- Invert the Image
Apply CT to set the basic tone scale and color saturation
At this point, I really wanted to enhance the pillars and the spider web. I thought the best tool for this was the PS Camera Raw Effects tools of Clarity, Texture, and Dehaze. I normally do this as part of my final ‘polishing’, but I thought I would do some of that here in order to avoid impacting the stars.
- Export nSHO Starless images as a 16-bit TIFF file
- Import to PS
- Use the Camera Raw filter to access Clarity, Texture, and Dehaze tools while selecting each pillar with the lasso and a 100-pixel feather.
- Save the TIFF image again
- Import the TIFF image back into PI

Params used to create the initial WarmMask

WarmMask after CT Boost (click to enlarge)

The Params used to create the initial CoolMask

CoolMask after CT boost (click to enlarge)

After NarrowbandNormalization (click to enlarge)

Global SCNR Green at 1.0 (click to enlarge)

After global CT Adjust (click to enlarge)

Run LHE with WarmMask (click to enlarge)

NarrowbandNormalization Parameters used.

Apply CT with the WarmMask (click to enlarge)

CT with the CoolMask in place (click to enlarge)

Global Sharpening using MLT set up this way(click to enlarge)

After MLT Sharpening run TWICE! (click to enlarge)

After PS run with the Clarity, Texture, and Dehaze tools

8. Add the Stars Back In

Using the ScreenStars Script, add stars back into our SHO starless image.

The script used to add the images back in,

Final Image ready for Photoshop Polishing!

9. Export the Image to Photoshop for Polishing

Save the image as a TIFF 16-bit unsigned and move to Photoshop
I did not like the composition, and after some experimentation, I settled on rotating the image 90 degrees counterclockwise and cropping it to a 4:5 aspect ratio.
Make final global adjustments with Clarify, Curves, and the Color Mixer - slight tweaks really
Use the lasso tool with a feather of 100-pixel and select small detail areas of the image, and enhance with the Clarity, Texture, and color mixer tools.
Added Watermarks

Export Clear, Watermarked, and Web-sized JPEGs.

The Final Image!

10. Final Comments

This was simpler processing because of the long integration times - I barely used any NXT.

This is also the first time that I exported my starless SHO image to Photoshop so I could use the Caerma Raw Effects tools on the image without the stars being impacted. I thought this worked out well and will likely do that again in the future.

I added some zoom and Cropped images of the pillars show I could show them to you in detail - but they looked so good, I may make a seperate project where I just focus on those alone!

Back to the SH2-171 Page

Alternatively, you can use the back arrow to return to the SH2-171 Main page, or you can use the menu at the top of the page to continue your navigation.

Thanks,

Pat

Patrick A. Cosgrove

A retired technology geek leveraging his background and skills in Imaging Systems and Computers to pursue the challenging realm of Astrophotography. This has been a fascinating journey where Art and Technology confront the beauty and scale of a universe that boggles the mind…. It’s all about capturing ancient light - those whispering photons that have traveled long and far….

https://cosgrovescosmos.com/