NBRGB Combination

Purpose and expected result

NBRGB Combination injects up to three registered monochrome narrowband masters into the corresponding red, green, and blue planes of a broadband RGB still. It uses the supplied effective filter bandwidths to estimate a continuum-corrected line plane, boosts that structure around its median, matches it to the boosted broadband channel when enough samples exist, and keeps the stronger value at each pixel.

The expected result is a new RGB still named <RGB target> - NBRGB. The source RGB and narrowband views remain unchanged. This is not channel assignment and it is not a spectral response model: the process does not inspect central wavelengths, transmission curves, exposure normalization, WCS, registration, or point-spread-function differences.

At a glance

Item	Current behavior
Menu path	Process > Color Spaces > NBRGB Combination
Enabled when	A three-channel RGB still is active, the same process is not already attached, and no attached process holds exclusive access
Inputs	One RGB still plus at least one open, same-size, grayscale still selected for Red, Green, or Blue; narrowband pixel types may differ from the RGB type
Outputs	A new same-size RGB still named <target> - NBRGB in the target's representation; Take snapshot creates another still; no file is written directly
Recommended image state	Registered, consistently calibrated linear masters with meaningful effective bandwidths and compatible intensity scales
Preview support	Always-on asynchronous preview with histogram and display autostretch; starts with a centered Preview area of up to 512 x 512 pixels
Sequence support	Not supported: the registered action needs a still image, and a sequence run is refused by name
Mask support	Not applied: the result is a new image, not an edit of the target
External dependencies	None; the bundled engine performs the calculation without a tool, model, catalog, or network service

Before you start

• Register and crop every narrowband master to the RGB target. The selectors check only grayscale format and exact width/height; they do not compare stars, WCS, pixel scale, orientation, crop origin, or PSF.
• Use linear, background-prepared data with consistent normalization. Continuum subtraction has a physical interpretation only when the RGB and narrowband samples retain a meaningful intensity relationship.
• Enter effective passband widths in nanometres. RGB bandwidth is one shared approximation for all three broadband planes; each selected narrowband width must be smaller than it. The process does not derive widths from FITS headers.
• Match gradients, exposure scaling, and other acquisition differences upstream. The internal linear fit handles a final per-channel affine relationship; it is not a substitute for registration, background correction, or photometric response calibration.
• Leave Non Linear rescale off for a physically interpretable linear start. Despite its label, it performs repeated full-plane min/max normalization; it does not linearize nonlinear data.
• Use a duplicate or Image History only if you need an extra safety copy of the inputs. Apply already creates a new image and does not replace the RGB target.

Procedure

1. Activate the registered linear RGB still and open Process > Color Spaces > NBRGB Combination. Confirm the target under RGB.
2. Select at least one same-size mono master under Red, Green, or Blue. Leave unused channel selectors at No image; those RGB planes pass through unchanged.
3. Enter the broadband effective width in RGB bandwidth and each selected narrowband filter width in its Bandwidth field. Confirm every narrowband value is lower than the RGB value.
4. Start with each selected Scale at 1.20, Reject low at 0.000, Reject high at 0.920, and Non Linear rescale off.
5. Keep Preview on NBRGB to judge the combination. Use RGB, NBr, NBg, and NBb to inspect the registered inputs. An unselected narrowband Preview mode falls back to the RGB source.
6. Move or resize the checked Preview area over background, bright emission, and star-rich structure. Outside the outlined area the preview remains the original RGB; uncheck the control to calculate a full-image preview.
7. Adjust one channel's Scale at a time. If the fit follows saturated or clipped structure poorly, narrow the Reject interval while retaining enough ordinary pixels for a fit.
8. Compare processed/original views with Switch image, keep one display stretch, then select Apply. Wait for <target> - NBRGB to appear; the run shows no progress dialog and has no Cancel button, and closing the window stops it.

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
Histogram plot	Graph, normalized intensity/count	Current preview; RGB channels overlaid	None	Binning comes from Plot resolution	Shows the mask-aware preview distribution and approximate endpoint-bin clipping	Always present	Recalculation adds work; endpoint counts depend on binning	Display only; preview RGB	Recomputed after preview or resolution changes
Left-drag in histogram	Graph gesture	No readout	None	Hold left button and move in graph	Shows normalized coordinate readout	Histogram always present	Diagnostic only	Display only	Ends on button release
Middle-drag in histogram	Graph gesture	Fitted/unpanned	None	Hold middle button and drag	Pans the graph	Useful after zooming	Display cost only	Display only	Until reset/window close
Ctrl+mouse wheel in histogram	Graph gesture	Fitted size	None	Up 1.20x; down 0.8x; wheel without Ctrl scrolls	Zooms around the cursor	Interactive graph enabled	Larger graph needs more rendering area	Display only	Window lifetime
Zoom in	Toolbar action	Fitted size	None	Each selection multiplies size by 1.30	Enlarges plot	Available while idle	Plot rendering only	Display only	Window lifetime
Zoom out	Toolbar action	Fitted size	None	Each selection multiplies size by 0.70	Shrinks plot	Available while idle	Plot rendering only	Display only	Window lifetime
Zoom reset	Toolbar action	—	None	One action	Fits graph and resets scrolling	Available while idle	Plot rendering only	Display only	Immediate
Show grid	Toggle	Checked	None	Checked/unchecked	Shows or hides graph grid	Available while idle	Display-only aid	Display only	Window lifetime; process Reset does not change it
Show clipping info	Toggle	Checked	None	Checked/unchecked	Shows or hides endpoint-bin counts and percentages	Available while idle	Counts are bin-based diagnostics	Display only	Window lifetime
Absolute scales	Toggle	Unchecked	None	Checked/unchecked	Checked normalizes each visible histogram channel to its own peak	Available while idle	Can conceal relative RGB strength; never changes pixels	Display only	Window lifetime
Draw histogram areas	Toggle	Unchecked	None	Checked/unchecked	Chooses filled-area or line rendering	Available while idle	Filled areas can obscure overlaps	Display only	Window lifetime
Show histogram	Toggle	Checked	None	Checked/unchecked	Shows or hides histogram curves	Available while idle	Display-only	Display only	Window lifetime
Plot resolution	Combo box, bins	8-bit (256)	None	6-bit (64), 7-bit (128), 8-bit (256), 9-bit (512), 10-bit (1024), 12-bit (4096), 14-bit (16K), 16-bit (64K), 100 levels, 1000 levels, 10000 levels	More bins show finer distribution	Available while idle	Higher counts increase histogram memory/rendering; processing precision is unchanged	Display only	Window lifetime
RGB	Target image selector	Attached active RGB still	None	Open three-channel RGB still	Supplies all three broadband planes, output dimensions/type, metadata base, mask, and output-name stem	Registered action requires an active RGB still; changing target rebuilds narrowband lists	Wrong target invalidates registration; source remains unchanged on Apply	Preview/Apply source; all RGB channels; still only	Attachment lifetime; Reset does not change it
RGB bandwidth	Double spin box, nm	100.00	None	0.10..1000.00; step 1.00	Larger values reduce the continuum fraction NB/RGB; smaller values subtract more RGB continuum	Must exceed every selected narrowband bandwidth by a nonzero margin	Incorrect effective width biases every selected channel	Preview/Apply; shared by R/G/B	Captured per run; Reset/success returns 100.00
Red / Image	Image selector	No image	None	Open, non-sequence grayscale image with target width/height	Enables narrowband injection into red	Apply needs at least one selected channel; list rebuilds on image/target lifecycle changes	Misregistration creates red halos/double stars; adds full-plane buffers	Preview/Apply; red only	Selection survives Reset/success while valid; not saved after close
Red / Bandwidth	Double spin box, nm	7.00	None	0.10..500.00; step 0.50; must be lower than RGB bandwidth	Higher values subtract a larger estimated continuum fraction	Ignored while Red / Image is No image	Near-RGB width amplifies noise through the small denominator	Preview/Apply; red only	Reset/success returns 7.00
Red / Scale	Double spin box, multiplier	1.20	None	0.00..10.00; step 0.05	Raises or lowers median-centered corrected red structure; 0 removes that boost but the matched/corrected maximum can still alter red	Ignored while Red / Image is No image	High values clip highlights and amplify noise/registration residuals	Preview/Apply; red only	Reset/success returns 1.20
Green / Image	Image selector	No image	None	Open, non-sequence grayscale image with target width/height	Enables narrowband injection into green	Same lifecycle/readiness rules as Red	Misregistration creates green halos/double stars; adds full-plane buffers	Preview/Apply; green only	Selection survives Reset/success while valid; not saved after close
Green / Bandwidth	Double spin box, nm	8.50	None	0.10..500.00; step 0.50; must be lower than RGB bandwidth	Higher values subtract a larger estimated continuum fraction	Ignored while Green / Image is No image	Near-RGB width amplifies noise through the small denominator	Preview/Apply; green only	Reset/success returns 8.50
Green / Scale	Double spin box, multiplier	1.20	None	0.00..10.00; step 0.05	Raises or lowers median-centered corrected green structure	Ignored while Green / Image is No image	High values clip highlights and shift color	Preview/Apply; green only	Reset/success returns 1.20
Blue / Image	Image selector	No image	None	Open, non-sequence grayscale image with target width/height	Enables narrowband injection into blue	Same lifecycle/readiness rules as Red	Misregistration creates blue halos/double stars; adds full-plane buffers	Preview/Apply; blue only	Selection survives Reset/success while valid; not saved after close
Blue / Bandwidth	Double spin box, nm	8.50	None	0.10..500.00; step 0.50; must be lower than RGB bandwidth	Higher values subtract a larger estimated continuum fraction	Ignored while Blue / Image is No image	Near-RGB width amplifies noise through the small denominator	Preview/Apply; blue only	Reset/success returns 8.50
Blue / Scale	Double spin box, multiplier	1.20	None	0.00..10.00; step 0.05	Raises or lowers median-centered corrected blue structure	Ignored while Blue / Image is No image	High values clip highlights and amplify blue noise	Preview/Apply; blue only	Reset/success returns 1.20
Reject low	Double spin box, normalized value	0.000	None	0.000..1.000; step 0.010; must be lower than Reject high	Raising it excludes darker boosted-channel samples from the affine fit	Fit also excludes zero/non-finite pairs and requires at least three usable samples	Too high can force the unannounced fit fallback	Preview/Apply; each selected channel fit	Reset/success returns 0.000
Reject high	Double spin box, normalized value	0.920	None	0.000..1.000; step 0.010; must exceed Reject low	Lowering it excludes brighter boosted-channel samples from the affine fit	Same fit/fallback rules as Reject low	Too low removes representative structure; too high admits clipping	Preview/Apply; each selected channel fit	Reset/success returns 0.920
Non Linear rescale	Checkbox, stage-wise min/max normalization	Unchecked	None	Checked/unchecked	Checked rescales continuum, boosted, and final selected-channel planes independently to [0,1] before their respective clamps	Applies to every selected channel; does not change Preview modes showing raw inputs	Removes absolute level/scale relationships, expands outliers, and can change color balance; three extra scans per selected channel	Preview/Apply before mask; selected channels	Reset/success unchecks it
Preview	Combo box	NBRGB	None	NBRGB, RGB, NBr, NBg, NBb	Chooses calculated result or an input inspection view; mono inputs are displayed as RGB	Unselected NBr/NBg/NBb falls back to RGB; active mask still blends the chosen display against RGB	Input modes diagnose registration but are not outputs and can look mixed under a mask	Preview only	Reset/success returns NBRGB
Preview pane	Image viewer	Mask-aware Preview-area composite	Inherits target display-autostretch settings at creation	Standard viewer zoom/pan plus linear/autostretch display	Shows the current ROI result pasted over original RGB; display autostretch never changes output samples	Always present; no Preview checkbox	Holds source/result/statistics buffers; full preview costs more than ROI	Preview only; current still	Window lifetime
Switch image	Preview-toolbar action	Processed preview shown	None	Click; Space; right-click; Ctrl+Shift+O	Toggles processed preview and original RGB	Available in preview pane	Display comparison only	Preview display only	Preview-window lifetime
Preview area	Preview-toolbar checkbox and movable ROI	Checked; centered up to 512 x 512	None	Checked/unchecked; drag/resize within target bounds	Checked processes only the corresponding crop from RGB, selected narrowband images, and mask, then pastes it over original RGB	Apply always processes the full image; source-only Preview modes crop the selected input too	Reduces preview work; outside the rectangle is deliberately not processed	Preview and Take snapshot only	Window lifetime; Reset does not clear it
Take snapshot	Preview-toolbar action	No snapshot	None	Click or Ctrl+Shift+K	Re-executes current settings and opens <target> - NBRGB Combination - SNAPSHOT; with Preview area checked, only that region is changed in the full-size snapshot	Snapshot uses current Preview mode, ROI, and active mask	Allocates a new still; source-only modes can create an inspection snapshot rather than an NBRGB result	New still; target unchanged	Each action creates a view
Apply	Button/action	Disabled until a valid RGB still, valid Reject interval, and at least one ready narrowband selection exist	None	One action	Captures current images/settings, runs in a background thread, and opens <target> - NBRGB	No progress dialog or Cancel; target selector and preview ROI/snapshot actions disable, but narrowband selectors, numeric options, Apply, Reset, and Close remain live; repeat Apply clicks are ignored while executing	Full-image vectors/intermediates can use substantial memory; wait for output before closing or interpreting later edits	Full still; active mask applies; never a sequence	Success resets numeric/options/Preview mode but retains valid selectors
Reset	Button/action	Enabled	None	One action	Restores bandwidths, scales, Reject limits, Non Linear rescale, and Preview mode	Does not clear RGB/narrowband selectors, histogram state, or Preview area; currently remains live during Apply	Schedules a new preview; does not alter the captured in-flight Apply	Configuration only	Immediate
Close	Button/action	Enabled	None	One action	Closes without applying current settings; during a background Apply it stops the run, which then opens nothing, and the window closes once the run has ended	Remains live during background Apply; wait for the output before closing if you want it	No output by itself	Window	Values are not persisted after destruction

There is no Apply progress dialog or visible Cancel action. The run carries a stop all the same: closing the window requests it, the engine's combination honours it, and a stopped run opens nothing.

How the algorithm works

1. Rectangular-bandwidth continuum estimate

The process handles Red, Green, and Blue independently. Let R_c be a normalized broadband sample in selected channel c, N_c the corresponding normalized mono narrowband sample, B_rgb the shared RGB bandwidth, and B_c the selected narrowband bandwidth. It defines

\[ q_c=\frac{B_c}{B_{rgb}},\qquad C_c=\frac{N_c-q_cR_c}{1-q_c}. \]

C_c is the estimated continuum-corrected narrowband plane. The denominator must be greater than 1e-6, so each narrowband width must be meaningfully lower than the RGB width. The model treats both filters as rectangular passbands and uses the corresponding RGB channel as the continuum proxy. It does not use central wavelength, measured transmission, sensor quantum efficiency, exposure, or a spectrum; bandwidth values are therefore user-supplied approximations.

Without Non Linear rescale, C_c is immediately clipped to [0,1] in a 32-bit float intermediate. With the option checked, it is first min/max-scaled over the complete current plane and then clipped.

2. Median-centered channel boost

Let m_c be the median of the clipped continuum-corrected plane and s_c the channel's Scale. The boosted broadband plane is

\[ G_c=R_c+s_c(C_c-m_c). \]

At s_c=0, G_c is the original RGB plane, but the later maximum can still admit the corrected/matched narrowband plane. Increasing Scale strengthens both positive and negative deviations around the narrowband median. The intermediate is again optionally min/max-scaled and always clipped to [0,1].

3. Guarded affine match

The process attempts an ordinary least-squares fit

\[ M_c=a_cC_c+b_c \]

from continuum-corrected samples to the boosted plane. A pair is eligible only when both values are finite and nonzero and G_c lies inside the inclusive Reject low/Reject high interval. The NBRGB guard requires at least three eligible pairs, variation in C_c above 1e-8, and a valid rejection interval. If those checks fail, M_c=C_c; the UI does not announce that fallback.

4. Maximum merge, rescale, and mask

The selected output plane is

\[ O_c=\operatorname{clip}_{[0,1]}\left(\max(G_c,M_c)\right). \]

When Non Linear rescale is checked, the maximum plane is min/max-scaled once more before the final clip. Unselected RGB channels are copied unchanged. There is no neighborhood kernel or boundary extension: the continuum equation, boost, and maximum are per-pixel, while the median, fit, and optional min/max operations use global statistics over the current full image or preview crop.

The shared mask is applied last. For mask weight W after optional inversion,

\[ RGB_{final}=RGB_{source}(1-W)+RGB_{NBRGB}W. \]

Precision and invalid samples

Input samples are read through normalized double access. Corrected, boosted, matched, and combined helper images are 32-bit float; the final image retains the RGB source's pixel type, so integer outputs quantize on write. Narrowband sources may have different pixel types because their normalized samples are converted independently.

There is no general NaN/Infinity repair. The fit rejects non-finite pairs, but continuum calculation, median selection, min/max rescaling, maximum, and final write do not define an astronomical bad-pixel policy for them. Repair or reject non-finite samples upstream, especially before enabling min/max rescaling.

Parameter interactions and starting points

Combination	Conservative starting point	Too weak looks like	Too strong or defective looks like	Adjustment order
RGB/NB bandwidths	Use documented effective widths; keep NB well below RGB	Continuum correction resembles raw NB	Noise/gradients explode as widths approach equality	Verify units and widths before Scale
Scale + continuum median	1.20, one channel at a time	Emission enhancement is subtle	Clipped cores, amplified noise, colored star residuals	Fix registration/background, then Scale
Reject interval + fit	0.000..0.920	Fit still follows unwanted bright structure	Too few accepted samples silently return un-fitted C_c	Exclude clipping while retaining broad ordinary structure
Non Linear rescale + channel balance	Off for linear masters	—	Each stage expands outliers and destroys cross-channel amplitude relationships	Use only as a deliberate nonlinear display experiment
Preview mode + active mask	Temporarily disable mask when comparing raw RGB/NB inputs	Registration differences are hidden by black mask areas	Input mode appears to be a hybrid of RGB and NB	Inspect source modes unmasked, then restore mask for NBRGB
Preview area + Apply	Tune several representative ROIs, then full preview	Local setting misses other structures	Full-image background/highlights behave unlike one ROI	Sample background, emission, and stars before Apply

Inputs, outputs, and metadata

• The target selector accepts only RGB stills. Each narrowband selector accepts non-sequence grayscale views with exact target dimensions and excludes the target. It does not check registration, WCS, pixel type, processing state, filter identity, bandwidth metadata, exposure, or PSF.
• Apply creates one new RGB still and leaves every source unchanged. The output dimensions and pixel type match the RGB target. No mask, continuum map, fit coefficients, report, preset, or direct disk file is produced.
• The result's metadata is built from the RGB source and every selected narrowband source. 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 RGB target's plate solution with its world coordinate (WCS) cards, so the viewer, the astrometry window and a new plate solve find it on the result. The solution describes the RGB target's grid; it does not prove that the narrowband sources were registered to it.
• If every input explicitly declares linear state, the output is marked linear RGB with nbrgb-combination provenance. If any input declares nonlinear, the output is marked nonlinear. Otherwise the combined state is unknown. The Non Linear rescale checkbox does not independently change that decision.
• The new view receives the execution description “Created NBRGB combination from RGB and selected narrowband channels.” Successful Apply then resets the numeric/options state while retaining valid source selections.
• Take snapshot follows the selected Preview mode. With Preview area checked, it creates a full-size still in which only the ROI is replaced; with RGB or a narrowband input mode selected, it is an inspection snapshot, not necessarily an NBRGB combination.

Performance

Work is linear in pixel count for each of one to three selected channels. Each channel performs continuum correction, median selection, boosted-plane construction, fit eligibility/statistics, an optional least-squares fit, maximum merge, and output write. Non Linear rescale adds three full-plane min/max scans and normalization passes per selected channel.

The pixel loops use oneTBB, but selected channels are processed serially. Several full-size double vectors plus float intermediates coexist, alongside the RGB source/output, preview, mask, and histogram buffers. Memory therefore scales with image size and selected-channel count even though the mathematical pipeline is per-channel. Use the default Preview area to tune representative regions, then perform one full preview before Apply. No approved astronomical set was timed.

Worked example

• Evidence mode: Source- and focused-test-derived; not executed on project-owned astronomical data.
• Input condition: Red broadband samples are (0.20, 0.40, 0.60) and the registered mono red samples are (0.326, 0.562, 0.798).
• Settings: RGB bandwidth 100, Red bandwidth 10, Red Scale 1.20, Reject interval 0..1, and Non Linear rescale off.
• Continuum checkpoint: q=0.1, so corrected values are (0.34, 0.58, 0.82) and their median is 0.58.
• Boost checkpoint: Before clipping, G=R+1.2(C-0.58) gives (-0.088, 0.40, 0.888); clipping gives (0, 0.40, 0.888).
• Fit fallback: The zero boosted sample is ineligible, leaving only two nonzero pairs. NBRGB requires three, so the matched plane falls back to (0.34, 0.58, 0.82).
• Output checkpoint: The per-pixel maximum is (0.34, 0.58, 0.888). Green and blue are unchanged because they were not selected. These exact values reproduce the engine regression; they do not claim a visually suitable scale for real data.

Warnings and limitations

Bandwidths are an approximation, not filter metadata

One shared RGB width and three user-entered NB widths drive a rectangular- passband equation. AfterNight does not read central wavelengths or measured response curves and cannot verify that a selected master belongs to the labelled output channel.

Non Linear rescale changes the data three times

The option independently min/max-normalizes the corrected, boosted, and final selected-channel planes. It is not a display STF and does not merely prevent final clipping.

Apply has no progress dialog or Cancel button

The run is asynchronous, and this process shows no progress dialog and no Cancel button; closing the window stops the run, which then opens nothing. Most source/parameter/dialog controls remain live after Apply captures its parameters, and a later edit reaches the next run only. Wait for the new image before closing.

Equal dimensions are not registration

There is no translation, rotation, scale, distortion, WCS, PSF, or intensity compatibility check. Misregistered narrowband structure becomes colored halos and doubled stars while the result's acquisition facts still describe the sources.

Troubleshooting

Symptom	Likely cause	Fix
Menu action is disabled	Active view is grayscale or a sequence, no image is active, the same process is attached, or an exclusive process is attached	Activate an RGB still and close the conflicting process
Narrowband image is absent from a selector	It is RGB, a sequence, a different size, the target itself, closed, or not updated	Extract/convert to grayscale, register/crop to exact dimensions, and reopen/update it
Apply is disabled	No NB channel is selected, NB bandwidth is not below RGB bandwidth, Reject high is not above Reject low, or a selected view disappeared	Restore at least one valid source and correct the bandwidth/rejection values
Preview shows plain RGB	Parameters are not ready, or NBr/NBg/NBb was selected without that source	Select a ready narrowband channel and choose NBRGB
Narrowband input Preview looks mixed with RGB	The target's active mask is being applied even in source-inspection modes	Temporarily disable the mask while checking raw registration
Strong gradients or odd background offsets	Inputs were not background/intensity prepared, or the rectangular bandwidth approximation is poor	Correct gradients and scaling upstream; verify effective widths; reduce Scale
Fit seems to have no effect	Fewer than three finite, nonzero pairs survived the Reject interval, or the corrected plane is almost constant	Widen the interval and inspect clipping; understand that fallback uses corrected NB directly
Bright structures clip or color shifts strongly	Scale is high, bandwidth denominator is small, or Non Linear rescale expanded an outlier	Restore defaults, turn rescale off, verify widths, then raise one Scale gradually
Doubled stars or colored rims	Equal-size sources are not registered or have different PSFs	Register/crop upstream and consider matching star profiles before combination
Take snapshot is not an NBRGB result	Preview is on RGB/NBr/NBg/NBb, or Preview area is checked	Select NBRGB and uncheck Preview area for a full calculated snapshot
No progress window appears after Apply	NBRGB does not implement a progress dialog	Wait for <target> - NBRGB; use Preview area to estimate suitability before the full run

Related workflow steps

• Linear Match — prepare intensity relationships upstream when the NBRGB-specific internal fit is insufficient.
• Image Registration — align RGB and narrowband geometry before composition.
• NB Color Mapper — map and mix several narrowband layers directly rather than injecting them into a broadband target.
• Narrowband Palette Composer — explore palette matrices and presets from narrowband sources.
• Process Windows — shared preview, masks, snapshots, Apply, Reset, and image-history behavior.
• Image Viewer — display stretch, masks, and image-state inspection.

References and provenance

• AfterNight source and focused tests.
• The in-app About > Licenses text records this native NBRGB implementation as original AfterNight GPL code. No external process source was copied or translated for the engine API.