SH2-140 - The Hidden Nebula: Image Processing Walkthrough
Aug 9, 2026
My Image of the SH2-140 region.
This page is the Image Processing Walkthrought page for the SH2-140 2026 Imaging Project.
🔭 Project Summary
Target: SH2-140 — Sharpless 140 / S140 / LBN 505 / The Hidden Nebula
Capture Dates: July 11, 12, 22, and 23, 2026
Constellation: Cepheus • Distance: ≈ 2,500–3,000 light-years
Type: H II emission region and photodissociation region on the edge of the LDN 1204 molecular cloud
Imaging Period: July 11–23, 2026 • Total Integration: 12 h 23 m 00 s (SHO narrowband + RGB stars)
Filters: Ha · OIII · SII (Astronomik 36 mm 6 nm) + R · G · B (ZWO 36 mm LRGB Gen II)
Telescope: William Optics 132 mm f/7 FLT APO Refractor with P-FLAT7A 0.8× reducer/flattener
Camera: ZWO ASI2600MM-Pro (−10 °C; Gain 100 narrowband, Gain 0 RGB)
Mount: iOptron CEM60 on custom steel pier
Processing: PixInsight (SHO narrowband + RGB stars) & Photoshop
Location: Whispering Skies Observatory · Honeoye Falls, NY (USA)
Acquisition Notes: Ha: 49 × 300 s; OIII: 51 × 300 s; SII: 56 × 300 s; R: 36 × 60 s; G: 36 × 60 s; B: 36 × 60 s, all bin 1×1 at −10 °C; total 12 h 23 m 00 s after culling bad or questionable subs.
Image Note: This SHO narrowband image with RGB stars frames SH2-140, the bright ionization front of the Hidden Nebula, along with surrounding Lynds bright and dark nebulae including LBN 500, LBN 508, LDN 1201, LDN 1202, LDN 1203, LDN 1204, and reflection nebula vdB 153.
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
ACM Astro Color Mixer Script
ACE Astro Contrast Enhancer Script
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
SH2-140 SHO + RGB Stars Processing Flow
Sequential summary of the actual SH2-140 workflow, following the published SH2-140 image processing walkthrough: Blink review, WBPP 3.01 integration, SHO/RGB master construction, linear correction, RGB star preparation, STF-to-Histogram stretching, masked SHO color and contrast work, RGB star recombination, and final Photoshop output.
Processing this Image
(All Processing was done in PixInsight, with some final touches done in Photoshop)
1. Blink
General
Lots of satellite tracks - easy to handle.
Ha
4 frames removed - all for clouds.
OIII
0 frames removed. Airplane track on one sub - I left it. Little evidence of nebula signal.
SII
1 frame removed, for clouds.
Red
1 frame removed! Trees!
Green
1 frame removed! Trees!
Blue
1 frame removed! Trees!
Darks
All looks OK
Dark Flats
All looks OK
Flats
All good
2. WBPP 3.01
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 ran for 1:27:41. No errors.
WBPP Calibration View
WBPP Post Calibration View
WBPP Pipeline View
3. Load Master Images and Create Color Images
Load all master images and rename them.
Using ChannelCombination, create the Master SHO and RGB color images
Master Ha, OIII, and SII Images
Master SHO image.
Master R, G, and B images
Master RGB color image.
4. Initial Process of Linear SHO data
There were no obvious gradients in the Master SHO image, so I did not run DBE.
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 = 1.73 Y = 1.65. 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 - see params from snapshot below.
Run NarrowbandNormalization (see screenshot below for parameters used). Note: I usually go starless first, but in this workflow I ran NarrowbandNormalization before star removal.
Run SXT and remove stars - we are not going to use the narrowband stars, so no need to save them.
Measuring Star Sizes with PFSImage Script (click to enlarge)
BXT Settings Used. (click to enlarge)
NXT Panel used. (click to enlarge)
Master SHO Before BXT Correct Only, After BXT Correct Only, After BXT Full, After NXT
Master SHO Image (click to enlarge)
NarrowbandNormalization Parameters used.
After NBNormalization (click to enlarge)
SHO Starless Image.
5. Process the Linear RGB Data
Run DBE for the RGB 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.
Select a preview rectangle that samples the background sky, and then set up and run SPCC.
Use the Ideal curve
Use ZWO R, G, & B filter curves,
Run the PFSImage script to measure star sizes. X = 1.87, Y = 1.77. 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 - see params from snapshot below.
Run SXT and don’t save the RGB starless image - we are not going to use that one.
Master RGB DBE Sampling Plan (click to enlarge)
Before DBE (click to enlarge)
Master RGB after DBE (click to enlarge)
Master RGB Background subtracted (click to enlarge)
Measuring RGB star sizes.
Params used for BXT
SPCC Panel settings.
SPCC Regression Results.
Master-RGB Before SPCC (click to enlarge)
After SPCC (click to enlarge)
Master RGB before BXT Correct Only, After BXT Correct Only, After BXT Full, After NXT V3
Final Master RGB image - Before Star Removal.
Master RGB Star image after SXT.
6. Take RGB Stars Nonlinear
Use Seti Astro Star Stretch Script to stretch Stars
I decided to create three versions of the nonlinear star image. Then I came back and added one more.
Stars #1 used a stretch of 5.0 and a color boost of 1.0 (the default)
Stars #2 used a stretch of 6.0 and a color boost of 1.51
Stars #3 used a stretch of 7.0 and a color boost of 1.53
I then came back and created one more that was #4, and this was between 2 & 3 with a stretch of 6.5 and a color boost of 1.6
Star Stretch Script panel and params used for stars #1
StarStretch Params for stars #2
StarStretch Params for stars #3
Nonlinear RGB Stars image #1
Nonlinear RGB Stars image #2
Nonlinear RGB Stars image #3
7. Take the Starless SHO Image Nonlinear
Use the STF→HT method to take the SHO starless image nonlinear - see screenshot below for params.
Nonlinear SHO image
8. Process the Nonlinear SHO Starless Image
This is the big meaty step of this process. In this section, I will focus on getting Green/Magenta under control, nailing the tone scale and color separation, doing masked warm/cool refinement, and then ACM/ACE polish.
Create the WarmMask
Use the ColourMask Process with StartHue 328 and an end hue of 68, with a blur of 5
Apply CT to boost the mask
Create the CoolMask
Use the ColourMask Process with Start Hue 162 and an end hue of 259, with a blur of 5
Apply CT to boost the mask
Apply CT to set the basic tone scale and color saturation
Apply SCNR Green with a value of 0.9 to reduce the amount of green in the image.
Invert the image (make magenta regions look green)
Apply SCNR Green with a value of 0.9 to reduce the amount of green in the image.
Invert the Image
Apply CT for Tone and Color.
Apply the Warm Mask
Apply CT
Apply LHE1 with a factor of 64, contrast limit of 2.0, an amount of 0.61, and a histogram of 8 bits (This will bring up some finer detail)
Apply HDRMT with Level 5, To Lightness, Lightness Mask. Trying to tame the bright region and get some detail back.
Apply CT to restore contrast lost in the previous step.
Apply NXT (see params below)
Use ACM to adjust Warm and Cool Color positions. Texture did not help here as it seemed to just bring up the noise.
Use ACE to do some light Clarity and Dehaze
Export Image to Photoshop - I wanted to work on specific areas of the blue region and decided to use the lasso tool there to make the adjustment rather than creating a mask in PixInsight.
Apply NXT (see params)
Params used to create the initial WarmMask
Initial WarmMask (click to enlarge)
WarmMask after CT Boost (click to enlarge)
Initial SHO image(click to enlarge)
Apply CT (Click to enlarge)
Apply SCNR Green (click to enlarge).
After SCNR Green at 0.90 (click to enlarge)
Global CT Adjust. (click to enlarge)
After HDRMT 1 with the WarmMask (click to enlarge)
NXT Params used in the next step.
The Astro Color Mixer Script used to dial in the color. (click to enlarge)
ACE applied with some light Clarity and Dehaze.
Invert the image (click to enlarge)
Final Invert (click to enlarge)
After LHE1 with the WarmMask (click to enlarge)
Apply CT with WarmMask (click to enlarge)
After NXT (click to enlarge)
ACM adjustment (click to enlarge)
After PS Lasso blue area adjustments. (click to enlarge)
Apply NXT V3 (click to enlarge)
9. Add the Stars Back In
Using the ScreenStars Script, add stars back into our SHO starless image. Do this three times with the first star images created
Pick the best one. I went with star image #3 because I think you need the heavier stars to stand out in the rich nebulosity in the image. But I did not like how blown out the bright stars were. So I took Stars#3 and used CT on it to suppress the brighter stars. I then shared this version and the Stars#3 version with some Astro friends. Feedback strongly favored the smaller star version. Then I noticed that my method for reducing the bright stars’ brightness caused undesirable halos. So I created a new version 4 that used StarStretch to split the difference between Stars#2 (too small) and Stars#3 (too large). This was the final one I used.
The script used to add the images back in - with smaller stars.
Stars #1: The smaller stars just don’t work here - they are lost in the complexity of the region.
Stars #2: The middle-sized stars are not bad.
Stars #3: The largest size. I liked the overall balance but the larger stars do seem blown out. Most thought these larger stars were not the right choice.
Stars #4: This was a position right between Stars #2 and Stars #3. I chose this as the final image.
10. Export the Image to Photoshop for Polishing
Save the image as a 16-bit unsigned TIFF and move it to Photoshop
Added Watermarks
Export Clear, Watermarked, and web-sized JPEGs.
11. The Final Image!
The Final Image
12. Final Comments
I was happy with this process.
I make it a point to never look at other images of the target I am processing while I am working it. I don’t want other people's take on a target to influence what I do.
Once I was done, I did go look, and I found that my version of this target had a unique look compared to the others. I suppose you could call it unique-good, or unique-bad. I like the image, so you know which way I roll on this one!
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Thanks,
Pat
