June 4, 2026

🔭 Project Summary

Target: Hickson 61 — “The Box” / HCG 61 / NGC 4169 Group

Main Galaxies: NGC 4169, NGC 4173, NGC 4174, and NGC 4175

Capture Dates: April 20 and 21, 2026

Constellation: Coma Berenices • Distance: ≈ 170–200 million light-years for the main background members; NGC 4173 is likely foreground

Type: Compact galaxy group / apparent galaxy alignment featuring small, faint, distant galaxies arranged in a box-like pattern

Imaging Period: April 20–21, 2026 • Total Integration: 7 h 48 m 00 s (LRGB)

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

Telescope: Astro-Physics 155 mm Starfire EDFS f/5.3

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

Mount: iOptron Tri-Pier with column extension on custom steel pier

Processing: PixInsight (LRGB) & Photoshop

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

Acquisition notes: L: 128 × 90 s; R: 62 × 90 s; G: 60 × 90 s; B: 62 × 90 s at −15 °C, Gain 0; total 7 h 48 m 00 s after culling bad or questionable subs.

Image note: This LRGB image captures the compact apparent galaxy group Hickson 61, known as “The Box,” a tiny and faint arrangement of galaxies in Coma Berenices. The small angular size, faint surface brightness, and great distance of the background members make this a challenging but rewarding deep-sky target.

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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 Hickson 61 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:

Hickson 61 LRGB Processing Flow

Sequential summary of the Hickson 61 workflow, organized around the actual dependency chain from frame review and LRGB integration through linear preparation, targeted masking, nonlinear luminance and color refinement, star recombination, and final Photoshop polish. The processing emphasis was on recovering a small, faint galaxy group from imperfect data while controlling the background and correcting elongated stars.

1. Data Review and Linear Integration

1. Blink / Cull Subs Reviewed the L, R, G, and B frames from April 20 and 21, 2026; the final frame counts reflect bad or questionable subs removed before integration

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2. Check Calibration Frames Darks, dark flats, and flats were reviewed before preprocessing to confirm the calibration set was suitable for the LRGB data

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3. WBPP Integration Calibrated, registered, and integrated the L, R, G, and B data to produce clean master frames for the Hickson 61 field

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

2. Linear Luminance and RGB Preparation

Linear Luminance Branch

5. Prepare Linear L Applied background correction and early optical correction to the luminance master, preserving the small galaxy profiles and faint outer structure

6. Refine Linear L Used BlurXTerminator and NoiseXTerminator-style linear cleanup before separating the starless luminance from the star field for controlled galaxy processing

Linear RGB Branch

7. Prepare Linear RGB Applied background correction and color calibration to the RGB image, then performed early correction while the data were still linear

8. Refine Linear RGB Reduced linear noise and prepared a clean starless RGB image; RGB stars were saved separately for later star-color preservation and recombination

Saved Star Branch

Saved RGB Stars RGB stars were retained from the star-removal step so the final image could use natural star color without letting the stars dominate the tiny galaxy group

Star Stretch Branch

9. Stretch RGB Stars Stretched and adjusted several RGB star versions separately, keeping the stars controlled so they support the field without overwhelming Hickson 61

3. Targeted Mask Construction

10. Create RangeMask Used RangeSelection to isolate the hot bottom-left gradient / light-pollution artifact so it could be controlled without damaging the rest of the image

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11. Build GAME Masks Used GAME to create targeted masks for the Box region, the left-side field, the bottom-left galaxy area, and the top-right galaxy area

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12. Use Local Working Masks Worked with RangeMask, BoxMask, BottomLeftMask, LeftMask, and TopRightMask to apply local adjustments without globally altering the full field

4. Nonlinear Luminance Processing

13. Stretch Starless L Stretched the starless luminance image carefully to bring out the very small, faint galaxy structures without flattening the background

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14. Background Control Used tone-curve adjustments to keep the sky background dark and even while managing the bottom-left artifact

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15. Local Galaxy Detail Applied masked local-contrast enhancement to improve visibility of the compact galaxy shapes and small-scale structure in The Box

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16. Final Luminance Tuning Balanced sharpening, noise control, and contrast so the galaxies remained crisp but not overprocessed

5. Nonlinear RGB Processing and LRGB Build

17. Stretch Starless RGB Stretched the starless RGB image separately to establish the base color image without star interference

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18. Initial RGB Tone and Color Adjusted color balance and saturation conservatively, keeping the galaxies natural while maintaining separation from the dark background

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19. Add Luminance Combined the processed luminance with the RGB image to form the main LRGB result

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20. LRGB Noise Control Applied additional noise reduction after the LRGB build to smooth the background while preserving the small galaxies

6. Local Refinement with Working Masks

21. BoxMask Work Refined the Hickson 61 Box region itself, emphasizing the small galaxy arrangement without artificially enlarging the members

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22. BottomLeftMask Work Worked on the bottom-left galaxy area and nearby background structure while keeping the adjustment localized

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23. LeftMask Work Applied local adjustments to the left-side field to balance the composition and manage features away from the main Box group

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24. TopRightMask Work Used a top-right working mask for localized tone and detail control without changing the entire image

7. Final Color, Cleanup, and Star Recombination

25. Final Color Balancing Made broad final color adjustments to the starless LRGB image, keeping the field neutral and the galaxies understated rather than over-saturated

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26. Cleanup Pass Cleaned small blemishes and distractions that competed with the tiny galaxy group, while avoiding changes to actual galaxy structure

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27. Final Star Adjustment Adjusted the saved RGB stars separately for brightness, color, and scale before recombination

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28. Add Stars Back Recombined the processed RGB stars with the starless LRGB image, comparing star-size versions and choosing the one that best balanced the field against Hickson 61

8. Final Output

29. Export to Photoshop Saved the PixInsight result as a high-bit-depth TIFF for final polishing and presentation work

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30. Crop and Polish Cropped tightly enough to make the Box group the visual center of attention while preserving useful surrounding field context

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31. Final Exports Created final clear, watermarked, and web-sized versions for the project page and sharing

Processing this Image

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

The main processing challenge for this image was rescuing a small, faint galaxy group from imperfect data. The AP155 optics performed well, but tracking problems left the stars noticeably elongated, and the field also contained a stubborn bottom-left gradient or local light-pollution artifact. The workflow focused on careful frame rejection, separate luminance and RGB preparation, aggressive but controlled star correction with BlurXTerminator, targeted masking for the Hickson 61 region and surrounding small galaxies, conservative local-contrast work, star recombination, and final Photoshop polishing.

1. Blink

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

Lum
- 5 frames removed for tracking.
Red
- 2 frames removed for tracking.
Green
- 5 frames removed for tracking
Blue
- 2 frames removed for tracking.
Darks
- All looked OK.
Dark Flats
- All looked OK.
Flats
- All good.

After culling, the final retained frame counts were L 128, R 62, G 60, and B 62.

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 58 minutes

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). There is a significant gradient leading to the bottom left corner. DBE took most but not all of it out.
Run BXT - Correct Only. This was the turning point in the project. The tracking errors were severe enough that the image might not have been worth continuing, but the Correct Only pass in BlurXTerminator recovered the star shapes far better than I expected.
Run the PFSImage script to measure star sizes. X = 1.86, Y = 1.71. 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 a little over 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 Correct Only

Full BXT

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=1.53 Y = 1.44. 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

After BXT Fix Only

Full BXT

After NXT

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 three levels of star stretch:
- 1.6 stretch, and 1.5 saturation boost.

Min Stretch RGB Stars (Click to enlarge)

7. Create Masks

Because the target was so small and the field contained uneven background structure, broad global adjustments were not enough. The rest of the processing depended on targeted masks.
Use RangeSelection to create a mask of the hot bottom-left corner of the field. See RangeSelection Parameters used below.
Use Game to create a mask covering the Box Region, the Left Region, and the Galaxies at the bottom-left and the top-right.

8. Process the Nonlinear Lum Starless Image

Apply CT to darken the background sky
There seems to be a circular artifact in the image. This is going to be a problem, and neither a DBE nor a Range Mask is handling it. I decided to export it to Photoshop and use the healing brush to carefully remove it.
Apply the RangeMask, then use CT to darken the bottom-left light corner.
CT for the whole frame - no mask.
Apply LHE with a scale of 22, contrast limit of 2.0, amount of 0.2, and an 8-bit histogram and the BoxMask.
Apply LHE with a scale of 22, contrast limit of 2.0, amount of 0.32, and an 8-bit histogram, and the LeftMask
CT with the BottomLeftMask
Apply LHE with a scale of 22, contrast limit of 2.0, amount of 0.32, and an 8-bit histogram and the BottomLeftMask.
Apply CT to TopRightMask
Apply LHE with a scale of 22, contrast limit of 2.0, amount of 0.52, and an 8-bit histogram and the TopRightMask.
Apply NXT V3 now (see parameters in the screenshot below).

9. Now Process the RGB Starless Image

Apply SCNR with the Green Channel to clean up the bottom-left corner
Adjust tone scale with CT
Adjust tone scale with CT with the LeftMask
Apply LHE with a scale of 22, contrast limit of 2.0, amount of 0.52, and an 8-bit histogram with the LeftMask
Apply LHE with a scale of 22, contrast limit of 2.0, amount of 0.3, and an 8-bit histogram with the BoxMask
Apply CT with the TopRightMask
Combine with the L image using the LRGBCombination tool with parameters used shown in the screen snap below.
Do an MLT Sharpening with the parameters show in the screen snap below.

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

10. Add the Stars Back In

Using the ScreenStars script, add the stars back into the starless LRGB image. I tested the small, medium, and large star versions to see which best balanced the star field against the very small Hickson 61 galaxies.
I chose the medium-star version.

11. Export the Image to Photoshop for Polishing

Save the image as a TIFF 16-bit unsigned and move to Photoshop
At this point, the image was technically complete, but the final presentation depended heavily on crop choice because Hickson 61 occupies such a small part of the full frame.
I decided to zoom in a lot to center the composition on the Box group itself. I feel there is another image in there that I might be able to extract as its own image, but we will see about that later
I then did a little polishing using the Camera Raw filter.
Added watermarks

Exported clear, watermarked, and web-sized JPEGs.

Back to the Hickson 61 Project Page

Alternatively, you can use the back arrow to return to the Hickson 61 project page, or you can use the menu at the top of the page to continue your navigation.

Thanks,

Pat

Hickson 61 - The Box - 2026 Image Processing Walkthrough.