PROCESSING GUIDE
OSC SHO Processing with Perfect Palette Picker
This guide documents an Astro Diver workflow for using complementary dual-band one-shot-color data to create and explore synthetic narrowband palettes in PixInsight. The L-eXtreme dataset supplies Hα + OIII information, while L-Synergy supplies SII + OIII. The two datasets remain separate through stacking, are registered precisely, and are then used to create Hα, OIII, and SII masters for palette development with Seti Astro tools, including Perfect Palette Picker.
About this guide
The workflow grew out of processing IC 1396, the Elephant Trunk Nebula. The goal is to preserve the underlying
Hα, OIII, and SII information so different synthetic narrowband interpretations can be explored later.
Workflow at a Glance
Why Complementary Dual-Band OSC?
OSC - One-Shot Color. An OSC camera records color information through a Bayer color-filter array in a single exposure. The workflow is not tied to a specific camera model.
The complementary-filter concept
Optolong L-eXtreme
Hα + OIII
Provides Hα and one OIII dataset.
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Optolong L-Synergy
SII + OIII
Adds SII and a second OIII dataset.
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Together
Hα + OIII + SII
Supports SHO-style and other synthetic narrowband palettes.
OSC and mono narrowband - different tradeoffs
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This approach is not intended to reproduce a dedicated monochrome SHO system exactly. A monochrome
camera with separate Hα, OIII, and SII filters records each channel directly and independently, generally
providing greater channel isolation, signal efficiency, and control over integration time for each line.
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Complementary dual-band OSC trades some of that channel independence for simplicity. It can use an existing
cooled color camera, requires only two complementary filters for this workflow, and records two selected
emission bands during each exposure. A complete mono narrowband setup may also involve a filter wheel and
multiple narrowband filters, so the two approaches differ in both acquisition architecture and system
complexity.
Key idea
Separate complementary-filter stacks and preserved Hα/OIII/SII masters give you flexibility to revisit the same
data with different palette interpretations.
What the emission lines represent
Hα traces ionized hydrogen and is often strongest. OIII traces doubly ionized oxygen and may reveal different
ionization structures. SII traces singly ionized sulfur and is often weaker, but can add useful structural
separation.
1.Stack & Register the Two Filter Datasets
Critical rule
Keep the L-eXtreme and L-Synergy datasets separate through calibration and stacking. Do not combine the raw
lights from both filters into a single WBPP stack.
Calibrate and stack each filter separately - WBPP
Run the L-eXtreme and L-Synergy lights as separate WBPP stacks with the appropriate calibration frames.
Inspect the input data and resulting masters for tracking failures, clouds, gradients, FWHM/eccentricity
problems, and other obvious defects.
What I'm looking for:
Two clean, independently stacked linear masters with enough usable signal to justify moving to extraction.
Weak-looking L-Synergy color is not by itself a reason to reject the dataset
Decision point:
SII may be substantially weaker than Hα. The real test comes after extraction: does the SII master contain
useful structure at acceptable signal-to-noise? If not, additional L-Synergy integration may be more valuable
than aggressive processing.
Register the two masters
The two filter masters must align essentially pixel-for-pixel before emission-line extraction. Use the stronger or
cleaner master as the registration reference. Use StarAlignment if needed and crop both masters to their
common usable field if framing differs.
What I'm looking for:
Stars and nebular structures coincident across both masters, with no meaningful framing mismatch that could
contaminate extraction or palette construction.
2.Conservative linear preprocessing
Keep both masters linear through emission-line extraction and initial palette construction. ImageSolve when
needed. Correct gradients conservatively with GraXpert/GX. BlurXTerminator can be used conservatively;
Correct Only is a sensible starting point before extraction. NoiseXTerminator can also be used when needed, but
weak SII deserves particular protection.
What I'm looking for:
Clean, aligned linear masters without obvious residual gradients or correctable optical blur, while retaining faint
low-SNR structure.
3.Extract Hα, OIII, and SII
Use Seti Astro DBExtract, or another validated dual-band extraction method, on the linear registered masters.
Select the sensor configuration that matches the OSC camera used.
• L-eXtreme master → Hα + OIII source data
• L-Synergy master → SII + OIII source data
• Preserve separate grayscale Hα, OIII, and SII masters.
• OIII is present in both dual-band datasets; a suitable extraction workflow can use information from both.
What I'm looking for:
Three usable grayscale masters containing distinct, believable nebular structure. Preservation of the extracted
line data matters more than whether any individual channel looks aesthetically impressive.
4.Inspect the emission-line masters
Use STF for inspection while the Hα, OIII, and SII masters remain linear. Do not permanently stretch them
merely to make the channels look equally impressive.
• Hα: inspect the main nebular structure and fine filaments.
• OIII: look for morphology that differs from Hα.
• SII: inspect carefully for genuine structure and noise; this may be the limiting channel.
Decision point
If SII is too weak or noisy to contribute meaningful structure, consider acquiring more L-Synergy data rather
than forcing the channel later.
5.Build a Reference, Then Explore Palettes
Create a baseline SHO reference
Before exploring alternative palettes, create and preserve a conventional SHO reference from the extracted
masters:
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          R = SII; G= Ha; B = OIII
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When Hα dominates, the initial SHO image may appear strongly green. That is normal. It is a mapped
representation of the three channels, not a finished aesthetic. Keep this reference without overwriting the
source masters.
6.Explore palettes - Perfect Palette Picker
Treat palette exploration as its own processing stage. Use Seti Astro Perfect Palette Picker with the preserved
Hα, OIII, and SII masters to preview different color mappings. Render several promising palettes into separate
images so they can be viewed at useful scale and, if desired, processed further.
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Do not feel compelled to choose only one result immediately. The strength of this workflow is that the same
emission-line masters can support multiple interpretations. Save the combinations that are visually interesting
and still preserve meaningful structural differences in the data.
What I'm looking for:
A short list - roughly 3 to 5 palette combinations - that look the most interesting while preserving useful Hα, OIII,
and SII structure. Render those candidates to images and compare them outside the PPP preview.
Decision point - choose the palette candidates worth developing
• Does weak OIII remain visible rather than being overwhelmed by Hα?
• Does SII contribute recognizable structure rather than only shifting global color?
• Do color transitions follow actual nebular morphology?
• Do faint structures survive the palette transformation?
About named palettes
PPP may include or inspire recognizable palette styles, but this guide is intentionally palette-agnostic. The
objective is to use PPP to explore and render combinations that serve the data, not to reproduce one named
palette.
7.Finish the Selected PPP Render
Verify the PPP Output State
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Do not assume that a Perfect Palette Picker output is linear or nonlinear based on the Linear Input Data setting alone. Before continuing, reset or turn off STF and inspect the rendered palette without a screen stretch.
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If the image remains normally visible:
Treat the PPP output as nonlinear. Continue with nonlinear processing such as CurvesTransformation, saturation and contrast adjustments, optional star separation, and final refinement.
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If the image becomes black or nearly black:
Treat the PPP output as linear. Apply a permanent stretch using HistogramTransformation and/or GHS before continuing with nonlinear processing.
Decision point:
Always verify the PPP output with STF off before choosing the finishing path.
8.Optional advanced finishing - star separation
Use StarXTerminator when independent control of nebula and stars will materially help. Inspect bright stars and
dense fields for holes, ringing, halos, or damaged fine nebular structure before continuing.
9.Refine the starless nebula
For an already nonlinear PPP render, favor restrained CurvesTransformation, targeted HistogramTransformation
adjustments, ColorSaturation, masks, and local refinements rather than treating the image as if it still needs its
first stretch.
10.Process stars and recombine
Process stars conservatively, then recombine with ImageBlend or another controlled method. If the stars
dominate, become too saturated, or expose StarX artifacts, return to the star layer rather than damaging the
nebula to compensate.
11.Final quality check
Inspect the full frame and several 100% regions before calling the image finished.
• Clipped or unnaturally empty background
• Excessive gold/orange saturation
• Electric, disconnected, or unnaturally dominant OIII color
• Residual green that distracts from the chosen palette
• Magenta, oversized, or excessively saturated stars
• Halos, holes, ringing, or other star-removal artifacts if StarX was used
• Oversharpened filaments or artificial local-contrast edges
• Excessive noise reduction, particularly where SII or OIII is weak
• Residual gradients or uneven background
• Color transitions that do not correspond to believable emission structure
Final question
Does the selected interpretation preserve the useful information in the Hα, OIII, and SII data and present it
coherently?
12.Files to preserve
• Independent L-eXtreme and L-Synergy stacked masters
• Extracted Hα, OIII, and SII grayscale masters
• Baseline SHO reference
• Top PPP palette renders
• Selected palette master
• Starless and star images if the advanced path was used
• Final processed image
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The Hα, OIII, and SII masters are especially valuable because alternate palettes can be developed later without
recalibrating or restacking the original light frames
Worked Example - IC 1396 / Elephant Trunk
The processing guide above is intentionally equipment-agnostic. This section documents the data used to
develop and test the workflow.
IC 1396 was the learning project for this complementary dual-band OSC approach. The project began as a
conventional SHO experiment and evolved into a PPP-based palette exploration workflow.
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Worked-example equipment and acquisition
• Askar 111F APO
• ZWO ASI533MC Pro cooled OSC camera
• ZWO AM5
• Optolong L-eXtreme: 244 x 90 s = 6 h 06 m
• Optolong L-Synergy: complementary SII + OIII dataset acquired separately
Main lesson
Separate complementary-filter stacks and preserved Hα, OIII, and SII masters let the same data be revisited through multiple palette interpretations without recalibrating or restacking the original light frames.
Lessons Learned
• Stack complementary filters separately.
• Keep the data linear through line extraction and initial palette construction.
• Preserve Hα, OIII, and SII masters permanently.
• Protect weak SII during denoising and preprocessing.
• Use PPP to explore and render multiple promising palette combinations before committing to one.
• Check whether a PPP render is already nonlinear before applying any additional stretch.
• Star separation is optional; use it when independent control materially improves finishing.
• Use settings as image-specific decisions rather than universal recipes.
Workflow reference