April 28 2026

🔭 Project Summary

Target: Messier 104 – The Sombrero Galaxy / NGC 4594

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

Constellation: Virgo • Distance: ≈ 28–30 million light-years

Type: Nearly edge-on spiral galaxy with prominent dust lane and bright central bulge

Imaging Period: April 11–21, 2026 • Total Integration: 11 h 00 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: 193 × 90 s; R: 89 × 90 s; G: 80 × 90 s; B: 78 × 90 s at −15 °C, Gain 0; total 11 h 00 m after culling bad or questionable subs.

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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 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:

M104 Sombrero Galaxy LRGB Processing Flow

Sequential summary of the M104 workflow, organized around the actual dependency chain from frame rejection through final Photoshop polish.

1. Data Review and Linear Integration

1. Blink / Cull Subs Removed thin-cloud frames and obvious defects across L, R, G, and B

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2. SubFrameSelector Rejected additional subs based on FWHM and detail degradation; dew trend was visible in the data

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3. WBPP 2.8.9 Calibrate • CosmeticCorrection • register • integrate • autocrop • maximum quality preset

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4. Build Master Images Load L, R, G, B masters and create 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-shrink values → NXT V3 → SXT star removal

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

Saved Star Branch

Saved RGB Stars RGB stars saved from SXT for later ScreenStars recombination

Star Stretch Branch

9. Create Star Options Use Seti Astro Star Stretch to make three RGB star versions with different stretch levels

3. Nonlinear Luminance Processing

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

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11. Tone and Contrast CurvesTransformation to darken sky • HDRMT to open highlights

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12. Local Detail LHE for smaller-scale detail • NXT V3 before sharpening

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13. Sharpen L MLT sharpening using the built-in linear mask

4. Nonlinear RGB Processing and LRGB Build

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

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15. Process RGB CurvesTransformation → HDRMT → LHE for tonal scale, highlight control, and detail

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16. Add Luminance LRGBCombination folds the processed luminance structure into the RGB image

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17. Final RGB Color Balance Additional CurvesTransformation to adjust galaxy highlights and reduce excess red balance

5. Final Assembly and Output

18. Add Stars Back ScreenStars with the preferred stretched RGB star version

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19. Export to Photoshop Save as 16-bit TIFF for final polish

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20. Crop and Polish Rotate and crop for composition • Camera Raw filter for final tonal polish

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21. Final Exports Add watermark • export 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 the very bright core and sharp dust lane against the much fainter outer halo of M104. I used a fairly conservative LRGB workflow: careful frame rejection, separate luminance and RGB preparation, star removal for nonlinear work, luminance-driven detail enhancement, and final star recombination before a light Photoshop polish.

1. Blink

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

Lum
- 8 frames removed for thin clouds.
Red
- 2 frames removed for thin clouds.
Green
- 3 frames removed for thin clouds.
Blue
- 4 frames removed for thin clouds
Darks
- All looks OK.
Dark Flats
- All looks OK.
Flats
- all good.

A total of 17 frames were removed during Blink.

2. SubFrameSelector

Getting critical details was crucial for this image, so I wanted to remove the subs that showed statistically significant detail degradation. To determine which frames, I used SubFrameSelector to examine the FWHM size of stars and removed those outside the confidence bands.

Note the nightly pattern of star sizes increasing as the night progressed - this is almost certainly a dew effect, and it was seen in each channel.

This was the first project where I could clearly see dew buildup overnight in the SFS FWHM plots for every channel - that’s what drove the aggressive frame rejection.

Now the red channel, where 9 frames were removed. A few frames were removed because their star sizes were too small. This is almost certainly due to clouds attenuating them - ones I missed during the Blink operation.

Now the Green Channel, where 9 frames were removed.

And finally the Blue channel, where 11 frames were removed.

A total of 45 frames were removed during the SFS Operation.

3. 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 option chosen except for linear defect
Enabled for Autocrop
I chose NOT to use Drizzle processing, even though I wanted the greatest possible detail. In the past, I have had problems using the RC-Astro set of tools with images from the SCA260 V2 when running Drizzle.
WBPP run in 1:44:28 - no errors

4. 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.

5. Initial Process of Linear Luminance data

Run DBE for the Lum linear 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 cleans up the stars at the corners. Not much to do in this image as the scope is very crisp.
Run the PFSImage script to measure star sizes. X = 4.47 Y= 4.37. 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

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

Master Lum Starless Image (click to enlarge)

6. 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 cleans up the stars at the corners. Not much to do in this image as the scope is very crisp.
Run the PFSImage script to measure star sizes. X=4.11 Y = 3.99. 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 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

BXT Full

NXT

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

7. 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 3 levels of star stretch so that later, we have a choice of what size stars to use.

The Star Stretch Script and parameters used for Stars_1 - with the lowest stretch.

The Star Stretch Script and parameters used for Stars_2 - with the next highest stretch.

The Star Stretch Script and parameters used for Stars_3 - with the highest stretch of all

8. Process the Nonlinear Lum Starless Image

Apply CT to darken the background sky
Open up the highlights by running HDRMT with levels=7, “To Lightness” checked, and “Lightness Mask” checked.
Apply LHE with a scale of 50, contrast limit of 2.0, amount of 0.16, and an 8-bit histogram. This helps bring out smaller details.
Apply NXT V3 now (see parameters in the screenshot below). I wanted to do this before sharpening and bringing out more detail.
Apply MLT Sharpening using the built-in linear mask (see params used in screenshot below)

9. Now Process the RGB Starless Image

Adjust tone scale with CT
Open up the highlights by running HDRMT with levels=7, “To Lightness” checked, and “Lightness Mask” checked.
Apply LHE with a scale of 36, contrast limit of 2.0, amount of 0.2, and an 8-bit histogram. This helps bring out smaller details.
Fold the L image in using LRGBCombination - see the screen snap of the LRGBCombination Panel to see the params used.
Apply CT to adjust the galaxy highlights.
The balance has gone kind of red, so I wanted to back off on that, and I used another CT application to do so.

10. Add the Stars Back In

Using the ScreenStars Script, add stars back into our RGB starless image.
I tried using all three levels of stars, and I found I like the look of the larger stars. I assessed this in the ScreenStars script (seen below) and then went with that look.

The script used to add the images back in,

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. Because I did not rotate the camera for this framing during capture, the galaxy came in sideways. I chose a rotation and a heavy crop to bring the galaxy into scale. I chose a rotation and a heavy crop to bring the galaxy into scale.
I then did a little polishing using the Camera Raw filter.
Added Watermarks

Export Clear, Watermarked, and Web-sized JPEGs.

Back to the M104 Project Page

Alternatively, you can use the back arrow to return to the Messier 104 page, or you can use the menu at the top of the page to continue your navigation.

Thanks,

Pat

Messier 104 - The Sombrero Galaxy 2026 - Image Processing Walkthrough