May 28 2026

🔭 Project Summary

Target: Leo Triplet — M65 / M66 / NGC 3628, with NGC 3593

Capture Dates: April 11, 20, and 21, 2026

Constellation: Leo • Distance: ≈ 30–35 million light-years

Type: Interacting galaxy group featuring two inclined spiral galaxies, one edge-on spiral galaxy, faint tidal debris, and nearby NGC 3593

Imaging Period: April 11–21, 2026 • Total Integration: 12 h 39 m 00 s (LRGB)

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

Telescope: Askar FRA400 72 mm f/5.6 Quintuplet Air-Spaced Astrograph

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

Mount: ZWO AM5 on custom steel pier

Processing: PixInsight (LRGB) & Photoshop

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

Acquisition notes: L: 128 × 90 s; R: 128 × 90 s; G: 125 × 90 s; B: 125 × 90 s at −15 °C, Gain 0; total 12 h 39 m 00 s after culling bad or questionable subs.

Image note: This wide-field LRGB image captures the main Leo Triplet galaxies, nearby NGC 3593, and the faint tidal tail extending from NGC 3628.

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Special Note

Welcome to the image-processing page for this project. You got here by following a link from the main Leo Triplet 2026 project report, and you can return to that page using your browser's back button.

Abbreviations Used

BXT BlurXTerminator 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

MLT Multiscale Linear Transform

PI PixInsight

PS Photoshop

SCNR Subtractive Chromatic Noise Reduction Process

‍ ‍SFS SubFrameSelector

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

Summary:

Leo Triplet LRGB Processing Flow

Sequential summary of the Leo Triplet workflow, organized around the actual dependency chain from frame review and integration through linear preparation, galaxy-specific masking, nonlinear refinement, star recombination, and Photoshop polish.

1. Data Review and Linear Integration

1. Blink / Cull Subs Screened L, R, G, and B frames for thin clouds and obvious defects; removed 1 L, 2 R, 2 G, and 2 B frames

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2. Check Calibration Frames Darks, dark flats, and flats were reviewed and found usable before preprocessing

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3. WBPP 2.8.9 Quality-first run: calibration, CosmeticCorrection, registration, integration, autocrop, no drizzle; completed without errors

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4. Build Master Images Loaded and renamed L, R, G, and B masters; created the linear RGB image with ChannelCombination

2. Linear Luminance and RGB Preparation

Linear Luminance Branch

5. Prepare Linear L DBE subtraction → BXT correct-only → PFSImage star-size measurement

6. Refine Linear L Full BXT with enhanced star reduction → NXT V3 → SXT star removal; luminance stars were not retained

Linear RGB Branch

7. Prepare Linear RGB DBE subtraction → SPCC color calibration → BXT correct-only

8. Refine Linear RGB PFSImage star-size measurement → full BXT → NXT V3 → SXT star removal; RGB stars were saved for later recombination

Saved Star Branch

Saved RGB Stars RGB stars saved from StarXTerminator for later processing and ScreenStars recombination

Star Stretch Branch

9. Stretch RGB Stars Used Seti Astro Star Stretch to take the RGB star image nonlinear, using a 1.6 stretch and 1.5 saturation boost

3. Galaxy Mask Construction

10. Create RangeMask Used RangeSelection to create a mask covering the main galaxies in the field

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11. Duplicate Galaxy Masks Made four copies of the RangeMask for galaxy-specific processing

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12. Isolate Individual Galaxies Used DynamicPaintBrush or Clone to remove the other galaxies from each mask, leaving one targeted galaxy per mask

4. Nonlinear Luminance Processing

13. Stretch Starless L Used the STF → HT method to take the luminance image nonlinear

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14. Background and Galaxy Tone Used CurvesTransformation to darken the background and applied CT through the RangeMask to refine the galaxies

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15. Local Detail Applied LHE with the RangeMask to enhance galaxy structure while limiting the effect to the target regions

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16. Noise and Final L Tweak Applied NXT V3 before sharpening/detail work, then finished the luminance branch with a final CurvesTransformation adjustment

5. Nonlinear RGB Processing and LRGB Build

17. Stretch Starless RGB Used the STF → HT method to take the RGB image nonlinear

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18. Initial RGB Tone and Color Used CurvesTransformation for tone scale and a second CT pass to boost overall color saturation

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19. Add Luminance Used LRGBCombination to fold the processed luminance image into the RGB image

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20. Apply NXT Applied NXT to the combined LRGB image before more targeted galaxy work

6. Galaxy-Specific Refinement

21. GalaxyMask4 Work Applied CT, LHE, and MLT sharpening to refine the selected galaxy structure

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22. GalaxyMask1 Work Applied LHE and CT to adjust local contrast and tone in the selected galaxy

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23. GalaxyMask2 Work Applied LHE and MLT sharpening to improve detail in the selected galaxy

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24. GalaxyMask3 Work Applied CT to refine the selected galaxy without globally altering the full field

7. Final Color, Cleanup, and Star Recombination

25. Astro Color Mixer Used the prototype PixInsight Astro Color Mixer script for broad final color adjustment

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26. Photoshop Cleanup Round Trip Exported to TIFF, used Photoshop healing tools to remove star blemishes on the left side, then brought the image back into PixInsight

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27. Final Astro Color Mixer Pass Used Astro Color Mixer again to finalize color balance after cleanup

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28. Add Stars Back Adjusted the RGB stars with CT, then used ScreenStars to recombine the stars with the starless LRGB image; the larger-star version was preferred

8. Final Output

29. Export to Photoshop Saved the PixInsight result as a 16-bit unsigned TIFF for final polishing

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30. Crop and Polish Cropped for composition while keeping the small galaxy on the left in the frame; used Camera Raw for light final polish

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31. Final Exports Added watermarks and exported clear, watermarked, and web-sized JPEG versions

Processing this Image

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

The main processing challenge for this image was balancing several galaxies of different brightness and structure within the same wide field, while preserving the faint tidal tail extending from NGC 3628. I used a conservative LRGB workflow: careful frame rejection, separate luminance and RGB preparation, star removal for nonlinear work, galaxy-specific masks, controlled local contrast enhancement, final color adjustment, and star recombination before a light Photoshop polish.

1. Blink

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

Lum
- 1 frame removed for thin clouds.
Red
- 2 frames removed for thin clouds.
Green
- 2 frames removed for thin clouds.
Blue
- 2 frames removed for thin clouds.
Darks
- All looked OK.
Dark Flats
- All looked 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
Selected 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 correction options selected except linear defect correction.
Enabled Autocrop
I chose NOT to use Drizzle processing.
WBPP completed in 1:45:28 - no errors

3. Load Master Images and Create Color Images

Load all master images and rename them.
Using ChannelCombination, create the master RGB color image

The Individual L, R, G, and B master linear images.

4. Initial Processing of Linear Luminance Data

Run DBE for the linear luminance image. Use subtraction for the correction method. Choose a sampling plan that avoids the galaxies and bright stars. (see below)
Run BXT - correct only. This cleaned up the stars at the corners. There was not much to correct because the optics were performing well.
Run the PFSImage script to measure star sizes. X = 1.75 Y= 1.70. This will influence the values used in BXT.
Run full BXT. I used an enhanced set of values to shrink the stars more aggressively. These are about double the measured star sizes. See the BXT Panel Snapshot below.
Run NXT V3; refer to the parameters in the snapshot below.
Run SXT - no need to save the Lum stars, as we will not be using them.

Before BXT

BXT Fix Only

Full BXT

After NXT V3

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

Master Lum Starless Image (click to enlarge)

5.0 Initial Processing of Linear RGB Data

Run DBE for the RGB linear image. Use subtraction for the correction method. Start with the same sampling plan from the Lum run. Choose a sampling plan that avoids the galaxies and bright stars. (see below)
Select a background preview, then set up and run SPCC. See the SPCC Panel shot below for the parameters used.
Run BXT - Correct only. This cleaned up the stars at the corners. There was not much to correct because the optics were performing well.
Run the PFSImage script to measure star sizes. X=1.65 Y = 1.61. This will influence the values used in BXT.
Run Full BXT - I used 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 in the snapshot below.
Run SXT - this time we will save the RGB stars.

Master RGB before SPCC (click to enlarge)

Before BXT

BXT Fix Only

Full BXT

After NXT V3

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

6. Go Nonlinear

Using the STF → HT method, take the linear Luminance and RGB images nonlinear.
Using Seti Astro Star Stretch, take the RGB Star image nonlinear with two levels of star stretch:
- 1.6 stretch, and 1.5 saturation boost.

7. Create Galaxy Masks

Use RangeSelection to create a mask of all of the galaxies - see screen snap below for parameters used.
Make 4 copies of the RangeMask
Use DynamicPaintBrush or the Clone tool, remove 3 galaxies from each mask so that one galaxy is left targeted

8. Process the Nonlinear Lum Starless Image

Apply CT to darken the background sky
Apply CT with the RangeMask to adjust the galaxies a bit.
Apply LHE with a scale of 20, contrast limit of 2.0, amount of 0.333, and an 8-bit histogram and the RangeMask, so this is adjusting just the galaxies.
Apply NXT V3 now (see parameters in the screenshot below). I wanted to do this before sharpening and bringing out more detail.
Applied a final CT tweak.

9. Now Process the RGB Starless Image

Adjust tone scale with CT
Do a second CT to boost overall color saturation
Fold the L image in using LRGBCombination with the parameters shown below.
Apply NXT with the params shown below.
With GalaxyMask4:
- Apply CT
- Apply LHE with a scale of 16, contrast limit of 2.0, amount of 0.2, and an 8-bit histogram.
- Apply MLT Sharpening with the params shown below.
With GalaxyMask1:
- Apply LHE with a scale of 16, contrast limit of 2.0, amount of 0.3, and an 8-bit histogram.
- CT
With GalaxyMask2:
- Apply LHE with a scale of 16, contrast limit of 2.0, amount of 0.3, and an 8-bit histogram.
- Apply MLT Sharpening with the params shown below.
With GalaxyMask3:
- Apply CT
Apply the Astro Color Mixer to the image without a mask.
Export to TIFF
- Import into Photoshop and use the healing tool to remove star blemishes on the left side.
- Export to TIFF again and bring back into PixInsight.

Using the Astro Color Mixer to finalize color.

Astro Color Mixer Panel with Adjustments Made (click to enlarge)

10. Add the Stars Back In

Do a final CT Adjust on the star images to boost color, brighten things a bit and adjust red balance on the mid to high end.
Using the ScreenStars Script, add stars back into our RGB starless image.

11. Export the Image to Photoshop for Polishing

Save the image as a TIFF 16-bit unsigned and move to Photoshop
The big issue here is cropping. I decided to zoom in a bit and played with the composition I liked. I finally chose to keep the small galaxy on the left in the image.
I then did a little polishing using the Camera Raw filter.
Added watermarks

Exported clear, watermarked, and web-sized JPEGs.

Back to the Leo Triplet Project Page

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Thanks,

Pat

The Leo Triplet: M65, M66, and NGC 3628 - Image Processing Walkthrough.