Narrowband Palette Composer

Purpose and expected result

Narrowband Palette Composer prepares selected Ha, OIII, SII, and optional OSC stills, calculates 12 fixed palette formulas, and presents them as a synchronized grid or a large single preview. Per-role intensity controls multiply prepared Ha/OIII/SII values before mapping, clipping, and final global peak normalization.

The expected Apply result is one new 32-bit float RGB still named from the selected OIII, then Ha, then SII source and palette—for example, OIII - SHO Narrowband Palette. OSC-only input falls back to <palette> Narrowband Palette. Sources remain unchanged.

This is preset formula exploration, not a physical spectral model. Role names are user assertions: the process does not read filter identities, passbands, exposures, WCS, registration, or PSFs, and it does not provide a custom matrix editor.

At a glance

Item	Current behavior
Menu path	Process > Color Spaces > Narrowband Palette Composer
Enabled when	Always available as a top-level process; it can open without an active image or any open images
Inputs	OIII plus Ha or SII after optional OSC synthesis; all selectors accept open grayscale or RGB stills and may reuse the same view
Outputs	One new float RGB still for the selected palette; no source replacement, auxiliary channels, snapshot, report, preset file, or direct disk output
Recommended image state	Registered/cropped linear masters with gradients corrected; leave Input autostretch on for linear data unless you intentionally prepared display-ready inputs
Preview support	Automatic Palette Grid and Single Preview, built on a worker under an operation of their own once the inputs are chosen - the latest request wins and nothing older is shown; all 12 palettes at full resolution as 8-bit display conversions; no standard viewer/histogram/autostretch toolbar
Sequence support	Not supported by any source selector; no target sequence is needed to open the top-level window
Mask support	Not supported; the process explicitly disables ordinary target masking
External dependencies	No runtime tool, Python environment, model, catalog, or network service; SetiAstro lineage is recorded under References and provenance

Before you start

• Register and crop sources to one geometry whenever possible. Match sizes to reference only resizes width/height; it does not align stars, preserve aspect ratio, inspect WCS, or match PSFs.
• Select semantic roles carefully. RGB images in Ha/OIII/SII use red only. OSC1 synthesizes Ha from red and OIII from the green/blue mean; OSC2 synthesizes SII from red and OIII from the green/blue mean.
• Decide whether input pixels are linear. Input autostretch applies a fixed unlinked AfterNight stretch with shadows clipping -2.8 and target median 0.25, derived from the exact median and median absolute deviation of every sample; neither value is exposed in this window.
• Expect every palette to receive a global peak normalization. Even with Input autostretch off and intensities at 100%, Apply does not preserve the absolute scale of the masters.
• Remove unused selections rather than treating them as passive metadata. Every selected direct/OSC source participates in synthesis and in the metadata built for the output.

Procedure

1. Open the registered Ha, OIII, SII, and optional OSC stills, then choose Process > Color Spaces > Narrowband Palette Composer. No active target is required.
2. Select OIII plus Ha or SII. Alternatively, select OSC1/OSC2 sources that synthesize those roles. Watch Status and the warning text for RGB channel extraction, mono OSC broadcast, or resize notes.
3. Leave Input autostretch checked for linear masters. Turn it off for data already stretched or when you explicitly want only formula/clipping/global- normalization behavior.
4. Prefer same-size sources. If they differ, leave Match sizes to reference checked only when simple resampling is acceptable; full UI output uses Ha as dimension reference, then OIII, then SII.
5. In Palette Grid, select a tile to choose Apply's palette. Use the wheel and drag to inspect the same location/zoom across all formulas, or switch to Single Preview and choose from its bottom gallery.
6. Adjust Ha, OIII, and SII intensity from 100% one role at a time. The grid rebuilds all 12 formula outputs after each committed slider/spin change.
7. Inspect clipped highlights, noisy weak roles, and star alignment at the same zoom. The previews are normalized 8-bit displays of the float palette result, not a separate display STF.
8. Select Apply and wait for the named RGB view. Apply runs in a background worker but exposes no progress dialog or user Cancel action.

Complete parameter and action reference

UI label/action	Type and unit	Runtime default	Persisted-default exception	Valid values, step, or constraints	Effect of increasing, decreasing, or selecting	Dependencies and enable/visibility rules	Quality, artifact, runtime, memory, or disk trade-off	Scope: preview/apply, channel, mask, still/sequence	Persistence
Ha	Image selector, semantic role	No image	None; top-level process has no active-target auto-selection	Open grayscale/RGB still or No image; duplicates allowed	Supplies explicit Ha; RGB uses red; OSC1 contribution averages 50/50 with it	Readiness also needs OIII; if absent, prepared SII substitutes in Ha formula positions	Wrong role/misregistration creates false color; source preparation/cache costs full image	Grid/Apply; Ha role; still only; no mask	Window lifetime; tracks create/close/rename; Reset/success retains selection
OIII	Image selector, semantic role	No image	None	Open grayscale/RGB still or No image	Supplies required explicit OIII; RGB uses red; OSC contributions blend into it	OIII must exist after direct/OSC synthesis	Central to every formula; weak/noisy OIII can dominate cyan/blue after normalization	Grid/Apply; OIII role	Window lifetime; Reset/success retains selection
SII	Image selector, semantic role	No image	None	Open grayscale/RGB still or No image	Supplies explicit SII; RGB uses red; OSC2 contribution averages 50/50 with it	Readiness also needs OIII; if absent, prepared Ha substitutes in SII formula positions	Substitution makes SII-labelled formula positions reuse Ha, not an inferred sulfur signal	Grid/Apply; SII role	Window lifetime; Reset/success retains selection
OSC1	Image selector, helper role	No image	None	Open RGB/mono still or No image	Synthesizes Ha=R and OIII=(G+B)/2; mono is broadcast to RGB first	May satisfy both readiness sides by itself	Mixing OSC with explicit roles uses fixed 50/50 blends and can transfer broadband stars/gradients	Grid/Apply; Ha/OIII synthesis	Window lifetime; Reset/success retains selection
OSC2	Image selector, helper role	No image	None	Open RGB/mono still or No image	Synthesizes SII=R and OIII=(G+B)/2; mono is broadcast first	May satisfy both readiness sides by itself	If OSC1 and OSC2 both feed OIII, sequential averaging weights the later OSC2 contribution more	Grid/Apply; SII/OIII synthesis	Window lifetime; Reset/success retains selection
Input autostretch	Checkbox, fixed unlinked STF	Checked	Hidden defaults: target median 0.25, shadows clipping -2.8	Checked/unchecked	Checked stretches each prepared direct mono role independently and each OSC RGB channel independently before OSC extraction/mixing	Source/preparation change triggers a full grid rebuild	Makes linear signal visible but permanently changes palette pixels; unsuitable for already-stretched data; statistics/stretch cost per source	Grid/Apply before synthesis; no mask	Window lifetime; Reset/success checks it
Match sizes to reference	Checkbox	Checked	None	Checked/unchecked	Checked resizes prepared roles to Ha dimensions, then OIII, then SII; unchecked rejects remaining mismatches	OSC synthetic contribution may still be resized to an existing explicit channel before this policy is evaluated	Resampling changes sampling/PSF and can distort aspect ratio; unchecked is safer for detecting bad geometry	Grid/Apply; all prepared roles	Window lifetime; Reset/success checks it
Mode	Combo box	Palette Grid	None	Palette Grid, Single Preview	Changes presentation only; selected palette remains synchronized	Both modes always receive all 12 built frames	No engine rebuild; Single Preview devotes more screen area to one result	Preview display only	Window lifetime; Reset/success returns Palette Grid
Palette Grid tiles	Twelve selectable preview cards	SHO selected	None	SHO, HOO, HSO, HOS, OSS, OHH, OSH, OHS, HSS, Realistic1, Realistic2, Foraxx	Clicking a tile selects Apply palette and begins possible pan	Frames appear only after readiness/build; descriptions appear as hover tooltips	All frames are full-resolution 8-bit display copies of 12 float RGB results	Preview selection; Apply uses selected id	Selection shared with Single Preview; Reset/success selects SHO
Palette Grid mouse wheel	Shared zoom gesture	1x, centered	None	1.15^wheel_steps, clamped 1x..32x	Zooms the same source crop across every tile	Requires built frames	High zoom helps registration/clipping checks; no pixel recomputation	Preview display only	Resets when frames rebuild or double-clicked
Palette Grid left-drag	Shared pan gesture and selection	Centered	None	Drag any tile after selecting it	Moves shared normalized view center for every tile	Panning acts only above 1x	Enables formula comparison at identical coordinates	Preview display only	Until rebuild/double-click
Palette Grid double-click	Reset gesture	—	None	Left double-click	Resets shared zoom to 1x and center to image midpoint	Grid visible	Display-only	Preview display only	Immediate
Single Preview gallery	Twelve selectable thumbnails	SHO selected	None	Same 12 palettes	Chooses large preview and Apply palette; tooltip shows formula description	Single Preview mode; selection synchronized with grid	Gallery thumbnails use same built frames; no further engine run	Preview selection	Shared/window; Reset/success selects SHO
Single Preview main image	Large 8-bit presentation	Selected full-frame palette	None	Current selected palette	Displays a larger aspect-fitted view	Single Preview mode and built frames	Display conversion may downsample to fit; float Apply output is unchanged	Preview display only	Replaced on grid rebuild
Single Preview mouse wheel	Zoom gesture	1x, centered	None	Pointer over main image; 1.15^steps, 1x..32x	Zooms selected main image	Does not zoom gallery	Display-only inspection	Preview display only	Until rebuild/double-click
Single Preview left-drag	Pan gesture	Centered	None	Drag main image	Pans selected preview at zoom > 1x	Main image only	Display-only inspection	Preview display only	Until rebuild/double-click
Single Preview double-click	Reset gesture	—	None	Double-click main image	Resets zoom/center	Main image only	Display-only	Preview display only	Immediate
Ha	Linked slider + spin box, percent	100%	This is the intensity row, distinct from Ha source selector	0..200%; step 1; slider page 10; slider tracking off	Multiplies prepared/substituted Ha before selected formula	Spin updates immediately; slider commits value changes without continuous tracking	High values clip before normalization; 0 removes Ha-role contribution, including substituted SII in Ha positions	All 12 grid formulas and Apply; semantic Ha factor	Window lifetime; Reset/success returns 100%
OIII	Linked slider + spin box, percent	100%	Intensity row	0..200%; step 1; slider page 10; tracking off	Multiplies required prepared OIII before mapping	Same synchronization as Ha	High values often drive cyan/blue clipping and global scale; 0 can collapse OIII-dependent output	All palettes/Apply; OIII factor	Window lifetime; Reset/success returns 100%
SII	Linked slider + spin box, percent	100%	Intensity row	0..200%; step 1; slider page 10; tracking off	Multiplies prepared/substituted SII before mapping	Same synchronization as Ha	High values clip SII positions; with SII missing, this scales substituted Ha in SII positions	All palettes/Apply; semantic SII factor	Window lifetime; Reset/success returns 100%
Status	Read-only text	“Select OIII plus Ha or SII…”	None	Readiness/updating/ready messages	Reports missing roles, grid update, or selected-palette Apply readiness	Changes with selection/build state	Diagnostic only; not a progress percentage	Window state	Recomputed; not saved
Warning details	Read-only wrapped text	Empty	None	Preparation warnings or caught build error	Reports RGB-red extraction, mono OSC broadcast, synthesis resize, final reference resize, or grid failure	Cleared on invalid readiness/new request; successful grid uses first result's preparation warnings	Warnings can explain silent-looking role/resample changes; Apply itself has no report	Grid/preparation diagnostics	Recomputed; not saved
Busy spinner	Activity indicator	Inactive	None	Automatic during grid rebuild	Signals the worker's preparation and 12-palette build	The window stays responsive; a change during a build starts the next build, with the latest values, when this one lands	Does not provide percentage or cancellation	Preview-grid update only	Per rebuild
Apply	Button/action	Disabled until required synthesized roles exist	None	One action; disabled during worker execution	Captures current selected formula, settings, source names, and final output name, then creates a new RGB still in background	The selectors, preparation controls, preview selection, intensities, Apply, Reset, and Close are disabled until completion; the captured attachment/lock reference is OIII, then Ha, SII, OSC1, OSC2	Full-resolution prepare/map/normalize cost; no overwrite or direct disk use	Apply; still sources; no mask/sequence	Successful Apply retains selectors but resets options, mode, palette, intensities
Reset	Button/action	Enabled while idle	None	One action	Restores Input autostretch/Match sizes on, Grid mode, SHO, and all intensities to 100%	Does not clear source selectors or preview view center directly; disabled during Apply; emitted changes can rebuild grid	May trigger expensive rebuilds	Configuration	Immediate; no saved process instance
Close	Button/action	Enabled while idle	None	One action	Closes top-level process	Button is disabled during Apply; a window-close request still waits on the execution lock	Wait for the current calculation to finish	Dialog only	Ends window-local state/cache
Mask / snapshot / progress / Cancel	Absent facilities	Not available	None	—	No target mask blend, standard Switch image/Preview area/Take snapshot, Apply progress, or user cancellation	Custom preview and top-level process intentionally omit these controls	Protect/localize inputs upstream; wait for builds/runs to finish	All operations	None

How the algorithm works

Input preparation and channel synthesis

Every selected source converts to normalized 32-bit float. Direct Ha/OIII/SII mono is retained; direct RGB uses red and posts a warning. OSC RGB is retained; mono OSC broadcasts its one value into R/G/B and posts a warning.

When Input autostretch is checked, AfterNight calculates MAD statistics and applies its unlinked automatic stretch with shadows clipping -2.8 and target background 0.25. Direct RGB narrowband is reduced to red before this mono stretch. OSC is stretched per RGB channel before synthesis.

Prepared OSC roles are:

\[ Ha_{OSC1}=R_1,\quad SII_{OSC2}=R_2, \quad OIII_{OSCn}=\frac{G_n+B_n}{2}. \]

If an explicit role already exists, its synthetic addition is a fixed 0.5 explicit + 0.5 synthetic blend. OSC1 is processed before OSC2, so with an explicit OIII and both helpers the final OIII weights are 0.25 explicit + 0.25 OSC1 + 0.50 OSC2. A synthetic contribution with different dimensions is resized to the existing explicit role even when Match sizes to reference is off; a warning records this synthesis-specific resize.

After synthesis, OIII is mandatory and at least one of Ha/SII must exist. For formula mapping only, absent Ha uses prepared SII and absent SII uses prepared Ha. Their intensity controls remain semantic: Ha intensity scales the substitute used in Ha positions; SII intensity scales the substitute used in SII positions.

If final prepared dimensions differ and matching is on, full UI preview/Apply uses Ha dimensions, otherwise OIII, otherwise SII. Downsampling in either dimension selects area interpolation; pure enlargement selects bilinear. This can resize the other dimension and does not preserve aspect ratio automatically.

Palette formulas

Let H, O, and S be the prepared Ha, OIII, and SII samples after their respective intensity factors. Substitution has already occurred. Each row below produces raw (R,G,B) before clipping and final peak normalization.

Palette	Red	Green	Blue	Notes
SHO	S	H	O	Sulfur–hydrogen–oxygen direct assignment
HOO	H	O	O	OIII supplies green and blue
HSO	H	S	O	Direct assignment
HOS	H	O	S	Direct assignment
OSS	O	S	S	SII supplies green and blue
OHH	O	H	H	Ha supplies green and blue
OSH	O	S	H	Direct assignment
OHS	O	H	S	Direct assignment
HSS	H	S	S	SII supplies green and blue
Realistic1	0.5H + 0.5S	0.3H + 0.7O	0.1H + 0.9O	Fixed SetiAstro weighted blend
Realistic2	0.7H + 0.3S	0.3S + 0.7O	O	Fixed SetiAstro weighted blend
Foraxx, Ha present and SII absent	H	U H + (1-U)O	O	Two-channel branch, U=(HO)^(1-HO)
Foraxx, otherwise	T S + (1-T)H	U H + (1-U)O	O	T=C^(1-C), C=clip(O,10^-6,1); U=(HO)^(1-HO)

The Foraxx branch decision uses actual prepared availability after OSC synthesis, before missing-role substitution. Thus OSC1 can count as Ha and OSC2 as SII.

Clipping and global normalization

Every raw mapped component is independently converted with this policy before normalization:

• non-finite value → 0;
• value below 0 → 0;
• value above 1 → 1;
• otherwise unchanged.

The engine then finds one maximum M across every pixel and all three channels. If M>0, every component is divided by M and clamped again. Consequently, each nonblack result has at least one sample at 1. Intensities change relative role contributions, but clipping occurs first: once a raw component reaches 1, raising it further cannot increase the normalization maximum. When every intensity is zero, output remains black because M=0 skips division.

Parameter interactions and starting points

Combination	Start with	What it controls	Risk or diagnostic
Input autostretch + linear sources	On	Fixed per-source/per-channel display preparation	Turning it on for stretched data applies another nonlinear transform
Direct roles + OSC helpers	One source path first	Fixed synthesis and 50/50 averaging	Both OSC helpers make OIII averaging order-dependent; metadata exposures are not weighted by synthesis coefficients
Missing Ha/SII + intensity	100%	Substituted formula positions	Label remains Ha/SII even though the same other role supplies both positions
Match sizes + mixed geometry	Prefer pre-registration	Pixel dimensions only	Area/bilinear resize cannot repair translation, rotation, distortion, crop origin, or PSF
Palette + intensity	Select formula, then tune one role	Matrix input values	Global normalization can hide overall scale changes; inspect relative channels and clipping
Intensity above 100% + clipping	Raise slowly	Pre-matrix role strength	Values clip to 1 before peak normalization, flattening highlights and reducing further response
Palette Grid + Single Preview	Either	Presentation and selection	Same 12 frames; switching modes does not recalculate or change Apply formula
Grid spin edits + full resolution	Coarse adjustments	Rebuild frequency	Each committed change remaps/normalizes 12 full RGB images on a worker; the latest change wins

Inputs, outputs, and metadata

• Selectors accept valid mono/RGB stills of mixed pixel types and dimensions. Invalid/unsupported images, missing synthesized requirements, disabled resize with remaining mismatches, invalid hidden stretch options, and invalid intensity factors are rejected. UI intensity values are finite 0..2.
• Apply always creates one float RGB still. Naming prefers the selected OIII view, then Ha, then SII. OSC names are not used as stems, so OSC-only output is simply <palette> Narrowband Palette. The final name is captured with the pixel parameters before the background worker starts.
• The result's metadata is built from every selected source in role order Ha, OIII, SII, OSC1, OSC2. Its exposure is the sum of the exposures they state, recorded once. The object, instrument, telescope, observer, filter, sensor temperature, gain, binning, and exposure start are kept when every selected source states the same value and dropped otherwise, so a filter is kept only when every source shares it.
• The result keeps the header cards every selected source states identically, but no exposure, processing-state or identity card of a source; a card the sources state differently, or only some state, is dropped. It keeps the first selected source's plate solution with its world coordinate (WCS) cards only when the result keeps that source's size. When it does not - the first source was resized to the reference's size, or the reference was synthesized from a one-shot-colour source of another size - the result carries no solution, because that solution would label another pixel grid.
• The output is always marked nonlinear with operation provenance narrowband-palette-composer, including when Input autostretch is off.
• Apply records “Created <palette> Narrowband Palette Composer image,” then asynchronously resets preparation, presentation, palette, and intensities. Source selections remain.
• Palette Grid preparation warnings are visible only in the open process. Apply does not create a report or attach synthesis coefficients to output metadata.

Preview and execution behavior

Every source, preparation, or intensity change rebuilds the prepared Ha/OIII/SII channels and all 12 palettes. The grid is not built from reduced-resolution thumbnails: each float result is full resolution and is converted to an 8-bit QImage for the grid and single preview; Apply independently rebuilds the selected float result.

Grid generation runs on the thread pool, as one operation that prepares the channels and maps all formulas. The window shows a busy spinner and stays responsive; a change made during a build starts the next build, with the latest values, when that one lands, and only the latest grid is shown. Closing the window stops a build; there is no Cancel action. Apply is asynchronous but also has no progress object, so the engine's cooperative cancellation path is not exposed to the user.

Because this top-level window uses custom preview widgets, it has no target selector, display autostretch, histogram, Switch image, Preview area, Take snapshot, or mask blending. Selecting the first usable source chooses an internal attachment/lock reference in priority order OIII, Ha, SII, OSC1, OSC2; this is distinct from the Ha-first resize reference and OIII-first output name.

Performance

Preparation scales with pixels across all selected direct and OSC sources. Autostretch adds MAD statistics and a full transform per direct mono role or per OSC RGB channel. Synthesis, channel extraction, averaging, and resizing add more float mono buffers. Each palette performs a per-pixel matrix/Foraxx map, clipping, a serial global-maximum scan, and a parallel normalization pass.

The grid maps 12 palettes in parallel with oneTBB and keeps 12 full-resolution float RGB outputs at once before creating display QImages for both presentations. Every rebuild prepares the channels again and allocates the 12 outputs. Apply builds another selected output in a background thread. Peak memory therefore scales roughly with source pixels plus prepared mono channels, 12 float RGB palette images, and 8-bit preview frames. Close unused images, avoid unnecessary OSC/direct duplicates, and commit coarse intensity changes instead of stepping through many spin values. No approved dataset was timed.

Worked example

• Evidence mode: Source- and focused-test-derived; not executed on project-owned astronomical data.
• Prepared samples: Ha H=0.20, OIII O=0.40, SII S=0.80; Input autostretch off; intensities all 100%.
• SHO matrix: Raw RGB is (S,H,O)=(0.80,0.20,0.40).
• Clipping checkpoint: All components are finite and within [0,1], so none changes.
• Normalization checkpoint: Global maximum is M=0.80; division gives (1.00,0.25,0.50).
• Interpretation: These exact values reproduce the focused SHO engine regression. They show why even sub-unit inputs are rescaled; they do not claim that this single-pixel ratio is suitable for a real palette.

Warnings and limitations

Every preview change builds 12 full-resolution palettes

The grid is built on a worker while the window stays responsive. Every change prepares the channels again and rebuilds mapping, clipping, normalization, float outputs, and display frames for every formula. There is no preview Cancel.

Peak normalization follows clipping

Components above 1 are clipped before the shared maximum is measured. This prevents a strong outlier from setting a maximum above 1, but it also makes intensity response saturate and can flatten highlights.

Resize is not registration

Match sizes changes dimensions only and can alter aspect ratio. It does not align stars, preserve WCS, model distortion, or match focus/PSF. Prepare registered geometry upstream.

Apply has no progress or Cancel

Apply runs in the background. Source selectors, preparation controls, preview selection, intensities, Apply, Reset, and Close are disabled after parameters and the output name are captured. They are restored when the worker finishes; there is still no progress percentage or Cancel action.

Troubleshooting

Symptom	Likely cause	Fix
Window opens with empty selectors	This top-level process does not auto-select an active view	Choose sources explicitly; open supported mono/RGB stills if lists are empty
Apply is disabled	Synthesized inputs lack OIII or lack both Ha and SII	Select OIII plus Ha/SII, or use OSC1/OSC2 to synthesize the roles
Warning says RGB source uses red	RGB was selected in a direct narrowband role	Use a mono extracted master if red-only behavior is unintended
OSC contribution looks wrong	OSC1/OSC2 semantic role is wrong, mono was broadcast, or explicit/OSC data were averaged	Verify role and input color format; remove helpers while diagnosing
OIII seems biased toward OSC2	Explicit OIII, OSC1, and OSC2 are averaged sequentially	Use one helper or precombine externally with deliberate weights
Build fails with Match sizes off	Prepared channel dimensions differ after synthesis	Register/crop to exact dimensions, or enable matching only if simple resize is acceptable
Image is stretched/distorted but stars still do not align	Match sizes resampled dimensions without registration	Register and crop sources upstream; do not use resize as alignment
Preview looks much brighter than source	Input autostretch and mandatory peak normalization both change levels	Turn off Input autostretch if sources are already stretched; remember peak normalization always remains
Raising intensity stops changing highlights	Formula components already clipped to 1 before global normalization	Lower the dominant role and rebalance other roles
Missing SII palette resembles Ha	Engine substitutes Ha into SII formula positions	Supply real SII or choose an HOO-style formula intentionally
Palette selection changes but grid does not rebuild	Selection only chooses an already-built formula	This is expected; intensity/source/preparation changes trigger rebuild
The grid takes a while to update after a spin/selector change	All 12 full-resolution palettes are rebuilt on a worker	Wait for the spinner to clear; make coarse changes and reduce source dimensions upstream for experiments
Selectors, previews, intensities, or dialog buttons are disabled	A non-cancellable Apply is running	Let Apply finish before making another change
Output name lacks OSC source	Naming uses only OIII, Ha, then SII selector names	Rename the output after Apply if OSC-only naming needs context

Related workflow steps

• Narrowband Imaging — calibration, registration, gradients, normalization, palette choice, and later stretching.
• Image Registration — align source geometry before palette resampling/composition.
• Linear Match — prepare gross channel scale relationships before fixed formulas when appropriate.
• Channel Composition — direct user-chosen channel assignment without palette grid, OSC synthesis, or mandatory peak normalize.
• NB Color Mapper — per-layer HSV mapping, modifiers, and screen mixing instead of fixed matrices.
• NBRGB Combination — add continuum-corrected narrowband structure to broadband RGB.
• Image Viewer — inspect the created float RGB still with normal display tools after Apply.
• Glossary — SHO, HOO, palette, linear/nonlinear, autostretch, clipping, and normalization terminology.

References and provenance

• AfterNight source and focused tests.
• docs/dev/NARROWBAND_PALETTE_COMPOSER_PROVENANCE.md records the reviewed SetiAstro SASPro source snapshot and hashes, Franklin Marek attribution, and GPL-3.0 license. AfterNight implements the behavior with native C++ engine and Qt controls; Python runtime objects, PyQt widgets, icons, and the upstream SASPro UI assets are not included.
• The same attribution and port boundary are exposed in About > Licenses.