Star Mask

Purpose and expected result

Star Mask finds the stars of one image, or of every sequence frame, with AfterNight's fitted star detector and paints them into a new single-channel grayscale mask. Each accepted star becomes a smooth radial profile or a solid ellipse.

The expected result is a same-size mask named <target> - STARMASK, with white or bright areas over accepted stars and black elsewhere. The source is not modified. This is a detector-driven mask generator; it does not read a saved star list.

At a glance

Item	Current behavior
Menu path	Process > Mask Generation > Star Mask
Enabled when	An image or sequence is active; a launch is refused with a warning when another Star Mask window is already attached to it or an attached process holds exclusive access
Inputs	One grayscale or RGB (with or without alpha) still or sequence in any integer or floating representation. Stars are found in an RGB image's green channel, or in its CIE L* with Use Lightness. A filter-array (mosaic) image that has not been demosaiced is refused; configured sequence auto-debayer can supply RGB frames
Outputs	One new same-size, single-channel grayscale mask still or sequence in the target's representation; Take snapshot creates an auxiliary still; source pixels are unchanged
Recommended image state	A calibrated linear or consistently prepared star field; clipping, strong gradients, hot pixels, blur, and prior nonlinear processing change detection and measured widths
Preview support	Asynchronous preview of the mask over the whole image or an initial centered 600×600 Preview area, original/result switching, snapshot, display-channel selection, and display-only Linear/Autostretch
Sequence support	Yes; one captured parameter set is applied frame by frame into a new temporary sequence, with frame progress and Cancel
Mask support	No. An active image mask is deliberately ignored because this process creates a mask rather than blending a correction through one
External dependencies	None; the detector and the mask painter are built into AfterNight

Before you start

• Use a calibrated image with representative focus and a controlled background. Hot pixels, noise peaks, saturated cores, gradients, and stretched halos can be accepted as stars.
• Match Radius to the stars: it is half the width of the box a star must be the brightest point of. The searched picture, or the Preview area, must be more than 4 x Radius + 8 pixels wide and tall, or the run is refused; at the default Radius 5 that is more than 28 pixels.
• Decide whether the mask needs graded profiles or hard selection. Leave Shaped Areas checked for radial falloffs; uncheck it for solid ellipses. Growth, size, and Star Shape controls do nothing without Shaped Areas.
• For an RGB target, stars are found in the green channel by default; enable Use Lightness to search CIE L* instead.
• Keep the preview Display Mode identical when comparing settings. Autostretch changes only presentation, not mask samples.

Procedure

1. Select the target and open Process > Mask Generation > Star Mask.
2. Start from the defaults: Radius 5, Threshold 1.00, Roundness Threshold 0.50, Gaussian, and the optional ranges off. If an error says the searched rectangle is too small, lower Radius or enlarge the Preview area.
3. Keep Shaped Areas checked. At Zoom 100%, inspect missed faint stars, false hot-pixel/noise detections, saturated cores, and blends. Fix detection settings before changing mask growth.
4. Tune Percent Increase and Pixel Increase, then restrict Min/Max Size if required. Percent Increase is a direct radius multiplier: default 0.50 halves the measured base radius before adding pixels; it does not add 50%.
5. Compare the six Star Shape profiles. Use Switch image under the same Display Mode. Uncheck Preview area before the final full-frame check, because the area is searched on its own.
6. Select Apply. A progress window with Cancel appears; on success AfterNight opens the new mask view, resets the settings, and closes the process. The original remains unchanged. Save/export the mask if it must survive the session.

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
Radius	Candidate-search half-width, pixels	5	None	3..32; integer	Larger widens the box a star must be the brightest point of and skips a wider border; smaller targets compact stars	Detection group; locked during Apply	The picture or Preview area must exceed 4 x Radius + 8 pixels each way or the run is refused; large values cost more and lose a fainter star within Radius of a brighter one; small values split or truncate broad stars	Detection; still/sequence	Captured per execution; Reset/success return 5
Threshold	Background-noise multiplier	1.00	None	0.01..15.00; step 0.05; slider maps thousandths	Raises/lowers the candidate threshold B + 5 x Threshold x n	Detection group	Lower finds fainter/noisier candidates and costs more fits; higher misses faint stars	Detection plane	Captured; Reset/success return 1.00
Amplitude Range	Checkable group	Off	None	Off/On	Enables a window on the fitted amplitude	Detection group; child bounds apply only when checked	Useful against weak/noisy or clipped fits; a narrow window can reject all stars	Post-fit rejection	Captured; Reset/success turn off
Amplitude Range > Minimum	Fitted amplitude, normalized (full scale 1)	0.00	None	0.00..0.99; step 0.05	Higher rejects fainter fits	Amplitude Range on	Can suppress weak noise but remove faint stars	Post-fit rejection	Captured; Reset/success return 0.00
Amplitude Range > Maximum	Fitted amplitude, normalized (full scale 1)	1.00	None	0.01..1.00; step 0.05; a Maximum below Minimum is refused when the run starts	Lower rejects brighter fits	Amplitude Range on	Can remove clipped/bright stars or empty the list	Post-fit rejection	Captured; Reset/success return 1.00
Roundness Threshold	Minimum fitted axis ratio FWHMminor/FWHMmajor	0.50	None	0.01..0.95; step 0.05	Higher requires rounder stars	Detection group	High values reject elongated stars; low values admit trails/blends	Post-fit rejection	Captured; Reset/success return 0.50
Roundness Range	Checkable group	Off	None	Off/On	Enables an upper axis-ratio limit	Detection group	A narrow lower/upper band can empty the list	Post-fit rejection	Captured; Reset/success turn off
Roundness Range > Maximum	Maximum fitted axis ratio	1.00	None	0.01..1.00; step 0.05; a Maximum below Roundness Threshold is refused when the run starts	Lower rejects rounder fits above this bound	Roundness Range on; off means maximum 1.0	Usually leave off unless deliberately selecting elongation	Post-fit rejection	Captured; Reset/success return 1.00
Convergence	Solver iteration multiplier	1	None	1..3; integer	Allows each fit more solver iterations	Detection group	Can rescue difficult fits at CPU cost; a fit that does not converge is discarded	Per-candidate fit	Captured; Reset/success return 1
Relax PSF Checks	Checkbox	Off	None	Off/On	Skips the scan's symmetry and local-amplitude tests and the fit's width-estimate and residual checks; amplitude, beta, geometry, magnitude, and roundness checks still apply	Detection group	Retains more difficult stars but also blends and poor fits	Candidate scan and post-fit validation	Captured; Reset/success turn off
Profile Type	Selector	Gaussian	None	Gaussian, Moffat	Chooses the fitted PSF model; Moffat also fits its exponent beta	Detection group; Moffat enables Minimum Beta	Moffat can represent broader wings but fits one more parameter	Per-candidate fit	Captured; Reset/success return Gaussian
Minimum Beta	Moffat exponent floor	1.50	None	0.05..10.00; step 0.05	Higher rejects Moffat fits with heavier wings (lower beta)	Enabled only for Moffat	Too high rejects valid winged stars; too low admits unstable fits	Moffat post-fit rejection	Captured; Reset/success return 1.50
Use Lightness	Checkbox	Off	None	Off/On	On searches an RGB image's CIE L*; off searches its green channel; a grayscale image is always searched in its one channel	Detection group; meaningful for RGB (on grayscale it only adds , on the lightness to the history text)	L* adds a conversion and combines all channels; green may have higher sampling and signal on a one-shot-color camera	Detection plane only	Captured; Reset/success turn off
Shaped Areas	Checkable group	On	None	Off/On	On paints radial profiles; off paints solid ellipses whose samples are 0 or 1	Growth/size/shape children apply only when checked	Shaped profiles give graded, circular footprints; solid ellipses keep the fitted axis ratio and angle with hard edges	Mask painting only	Captured; Reset/success turn on
Percent Increase	Radius multiplier	0.50	Label suggests a percentage increase, but the value is used directly as a multiplier	0.01..1.00; step 0.05 with adaptive stepping	Scales the larger fitted FWHM to the painted radius; 0.5 halves it	Shaped Areas only	Small values under-cover stars	Shaped masks; all accepted stars	Captured; Reset/success return 0.50
Pixel Increase	Additive radius, pixels	0	None	0..99; integer	Adds a fixed number of pixels after Percent Increase	Shaped Areas only	Dominates small stars and can merge neighboring masks	Shaped masks	Captured; Reset/success return 0
Min Size	Smallest painted diameter, pixels	2	None	0..99; integer; a Min Size above Max Size is refused when the mask is painted	Raises the minimum accepted 2 x larger FWHM	Shaped Areas only	Rejects small stars/hot pixels	Shaped-mask star selection	Captured; Reset/success return 2
Max Size	Largest painted diameter, pixels	25	None	0..99; integer; must not be below Min Size	Raises/lowers the maximum accepted 2 x larger FWHM	Shaped Areas only	High values retain large/saturated structures; low values reject large stars	Shaped-mask star selection	Captured; Reset/success return 25
Star Shape	Selector	Truncated Bell	None	Bell, Truncated Bell, Linear, Truncated Linear, Cubic, Quadratic	Chooses the radial falloff function	Shaped Areas only	Changes core plateau, wings, cutoff, overlap, and transition width	Per-star shaped profile	Captured; Reset/success return Truncated Bell
Target Image	Image/sequence selector	Attached active target	None	Open eligible image or sequence	Changes the source, the Preview, and the image the new mask is made from and named after	Active target required; duplicate/exclusive launch gates apply; locked during Apply	Selecting the wrong target creates a mask for the wrong data	Detection source; active mask is ignored	Target lifetime; Reset unchanged
Preview	Checkbox	Checked	None	Checked/unchecked	Creates or removes the asynchronous mask preview	Remains interactive during Apply	Each run copies the target or the Preview area (plus a floating copy for integer images) and reruns detection and painting; a burst of changes collapses into one run with the latest values; Apply cancels a preview in progress; a refused preview reports its error	Preview only; still/current sequence frame	Window lifetime; Reset unchanged
Preview pane	Image viewer	Mask result, with Preview area on at start	None	Pan/scroll and actions below	Shows the generated mask without modifying the source; with Preview area on, the area's mask over the rest of the image, an RGB image shown as its luminance	Exists only with Preview	Holds source, mask, and display buffers and detector workspaces	Preview only	Window lifetime
Fit To Window	Preview-toolbar action	Preview fitted initially	None	Click or Ctrl+Shift+F	Fits the whole image	Preview required	Broad context can hide small missed/false detections	Preview display only	Viewer lifetime
Zoom In	Preview-toolbar action	Current scale	None	Click; relative 1.25x	Enlarges the mask	Preview required	Improves edge/core inspection	Preview display only	Viewer lifetime
Zoom Out	Preview-toolbar action	Current scale	None	Click; relative 0.8x	Reduces the mask	Preview required	Shows distribution but hides fine edges	Preview display only	Viewer lifetime
Zoom 100%	Preview-toolbar action	Current scale	None	Click; absolute scale 1.0	Shows one-pixel viewer scale	Preview required	Preferred for false detections, coverage, and edge profiles	Preview display only	Viewer lifetime
View Channel	Preview-toolbar selector	Grayscale, disabled for the one-channel result	None	Grayscale for current mask	Selects displayed component only	Output has one channel	Display-only	Preview display only	Viewer lifetime
Display Mode	Preview-toolbar selector	Inherits target Linear or Autostretch when created	None	Linear, Autostretch	Changes display only; Autostretch stretches the preview with the target image's statistics and stretch settings	Shown because this process supports a display stretch	Different stretches invalidate visual comparison	Preview display only	Preview-view state
Autostretch Settings	Preview-toolbar action	Starts from the target view's settings	None	Opens the preview's display-stretch settings	Tunes preview presentation only	Shown beside Display Mode	Can exaggerate weak mask wings/background; never changes output	Preview display only	Viewer-scoped, not a Star Mask parameter
Switch image	Preview-toolbar action	Mask shown	None	Click, Space, right-click, or Ctrl+Shift+O	Toggles mask/original	Preview required	Comparison only	Preview display; current frame	Preview lifetime
Preview area	Preview-toolbar checkbox	Checked; centered 600x600 when possible, labeled Preview: Star Mask	None	Checked/unchecked; move/resize area	Searches and paints only the area and shows it over the rest of the image	Preview required; disabled during Apply	Faster tuning, but the area is searched with its own sky, noise, and border, so stars near its edges can differ from a full-frame Apply; an area not more than 4 x Radius + 8 pixels each way is refused	Preview and snapshot	Window lifetime; Reset unchanged
Take snapshot	Preview-toolbar action	No snapshot	None	Click or Ctrl+Shift+K	Runs the current settings again and opens <target> - Star Mask - SNAPSHOT; with Preview area on, the snapshot is the composite the Preview showed	Preview required; disabled during Apply	Adds full detector/mask work and one auxiliary still; display stretch is not baked in; no lineage entry is added	New still; source unchanged	Each action creates a new view
Apply	Button/action	Enabled after initialization/reset updates	None	One action	Captures all controls, locks the target, finds and paints on a worker, opens the new mask still or sequence beside the target, resets, and closes after success	Target lock required; during the run every Detection and Shaped Areas control, Target, Apply, Reset, Close, and the preview's snapshot and area actions are disabled whether or not Preview is on	Detector cost plus mask painting; output allocation, and sequence encoding adds memory/disk	New mask still/sequence; never blends through an active mask	Run snapshot; nothing is stored between openings
Reset	Button/action	Enabled while idle	None	One action	Restores every detection/mask default listed above	Leaves Target, Preview, Preview area, and preview-toolbar state unchanged; checked Preview schedules a run	Can trigger a complete preview recomputation	Configuration only	Immediate; also after successful Apply
Close	Button/action	Enabled while idle	None	One action	Closes without creating the Apply output	Disabled during Apply; closing the window while a run is in progress stops it	A stopped run makes nothing	Window/execution	Settings discarded
Progress / Cancel	Progress window with a busy indicator for the current image and Cancel; a sequence run adds a second card showing Executing process in sequence. Frame i/N and the share of frames done	Created for every Apply	None	Cancel	Stops the run at the engine's next checkpoint: between scan bands, fitted candidates, painted rows, or sequence frames	Still or sequence Apply; the frame card appears only for a sequence	Nothing waits on the GUI thread	Still/sequence Apply	A stopped run opens no view and leaves no partial sequence; success opens the new mask and closes the process

How the algorithm works

Conceptual pipeline

1. The search plane is a grayscale image's only channel, an RGB image's green channel, or its CIE L* when Use Lightness is checked. Samples are read in normalized units with full scale 1: an unsigned integer divided by its largest code, a signed integer counted from its smallest code, and a floating sample as it is. The plane is searched as linear data whatever state the image records.
2. The detector measures the plane's sky level B and noise n, smooths the plane with a Gaussian of about 1.83 pixels, and lists candidates: points of the smoothed plane above the threshold that are the brightest point of their 2 Radius + 1 pixel box, are backed by enough bright neighbors, and pass the scan's symmetry checks.
3. Candidates are fitted with an elliptical, rotated Gaussian or Moffat PSF, brightest first. Fits outside the roundness or amplitude window, below Minimum Beta, wider than the scan's own width estimate, or with too large a residual are rejected, and a fit that does not converge is discarded. At most 20,000 stars are kept.
4. With Shaped Areas on, each accepted star passes the size filter, has its base radius multiplied and enlarged by pixels, then receives the selected radial profile. Overlaps keep the maximum mask value.
5. With Shaped Areas off, each accepted star becomes a solid ellipse from its fitted widths and position angle, painted at full value.
6. The result is one grayscale channel with the target's dimensions and representation. Apply records it as nonlinear with the operation star-mask.

Detection models

With UI Threshold s, the candidate threshold is

T = B + 5 s n.

Gaussian fits an elliptical Gaussian with its position angle. Moffat fits an elliptical Moffat profile whose exponent beta is fitted with the rest; a fit whose beta falls below Minimum Beta is rejected. Each accepted star has a major and a minor full width at half maximum (FWHMmajor, FWHMminor) and a position angle. Its roundness FWHMminor / FWHMmajor must lie between Roundness Threshold and the Roundness Range maximum (1 when the range is off). With Amplitude Range on, the fitted amplitude, in the same normalized units, must lie inside the range.

Shaped masks use the larger full width as the base radius, R_base = max(FWHMmajor, FWHMminor), and become circular even when the fitted star is elliptical. Solid ellipses instead keep the fit: each ellipse spans 4 x FWHMmajor along the major axis, has the fitted axis ratio, and is turned by the position angle. A pixel is painted with 1 when at least half of its area, estimated on a 4 × 4 sub-pixel lattice, lies inside the ellipse.

Growth, size, and profile equations

The size filter accepts a shaped star only when

Min Size <= 2 R_base <= Max Size.

The painted radius is then

R = Percent Increase x R_base + Pixel Increase.

Thus the default 0.5 is a half-radius multiplier, not a 50% addition. For distance d from the star's center to each pixel's center, the six profiles are:

• Bell: exp(-d^2 / (2 R^2)).
• Truncated Bell: min(1, exp(0.5) x exp(-d^2 / (2 R^2))).
• Linear: max(0, 1 - d / (3 R)).
• Truncated Linear: max(0, 1.5 - 1.5 d / (3 R)).
• Cubic: max(0, 1 - (d / (3 R))^3).
• Quadratic (implementation label): max(0, 1 - (d / (3 R))^4).

Each star is painted over the square reaching 3R from its center, and values are clamped to [0,1]. The four polynomial profiles reach zero at 3R; the two bells are cut at the square's edge, which leaves a small step of at most about 0.011 for Bell and 0.018 for Truncated Bell. Despite its UI name, Quadratic uses a fourth power.

Boundary and failure behavior

• The candidate scan skips a border of Radius pixels around the searched area, so a star peaking that close to the edge is not found. Painting is clipped to the image.
• A picture, or a Preview area, that is not more than 4 x Radius + 8 pixels wide and tall is refused with the reason, and no mask is made.
• An Amplitude Range Maximum below its Minimum, a Roundness Range Maximum below Roundness Threshold, and, with Shaped Areas on, a Min Size above Max Size are refused with the reason, and no mask is made.
• A filter-array (mosaic) image that has not been demosaiced is refused.
• No detections produce a black mask rather than an error.
• In the search plane, a pixel the image's own validity marks as not valid, or on an ordinary image a pixel holding NaN or an infinity, is replaced by the measured sky before smoothing, so it neither stops the run nor becomes a star. With Use Lightness, a pixel the image's validity rejects reads as black in the lightness plane instead.
• A run the session's memory budget cannot hold is refused with the reason and makes nothing.
• Detection and painting observe Cancel; a stopped run makes no mask and shows no error.

Parameter interactions and starting points

Combination	Conservative starting point	Too weak looks like	Too strong looks like	Adjustment order
Radius + picture or Preview area size	Radius 5, which needs more than 28 pixels each way	Broad stars truncated or split	Run refused on a small picture or area; a fainter star within Radius of a brighter one is lost	Match Radius to star width -> check the searched size -> enlarge the area or lower Radius
Radius + Threshold	Radius 5, Threshold 1.00	Broad/faint stars missing	Dense noise candidates, blends, slow fits	Match Radius to star width -> lower Threshold gradually
Roundness + Relax PSF Checks	0.50, Relax off	Useful elongated stars rejected	Trails/blends/poor fits retained	Tune Roundness -> inspect -> enable Relax only for diagnosed rejection
Gaussian + Moffat/Minimum Beta	Gaussian first	Broad wings fit poorly	Moffat becomes slow or rejects fits	Compare same field -> choose Moffat -> tune beta last
Detection + shaped growth	Fix detection first; then 0.50, 0 px	Accepted stars under-covered	Halos merge and protect background	Fix false/missed detections -> Percent Increase -> Pixel Increase -> size bounds
Shaped + solid output	Shaped Truncated Bell for graded protection	Wings too narrow	Hard edges or excessive merged coverage	Choose intended downstream use -> compare modes -> refine shape/growth

Inputs, outputs, and metadata

• Apply creates one new mask; it never replaces the still source. A sequence source creates a new temporary mask sequence and keeps the source sequence.
• Output width and height match the processed source frame, and the output has exactly one grayscale channel in the target's representation. A floating mask holds 0..1; an unsigned integer mask runs from 0 to the largest code, and a signed integer mask from the smallest code (unpainted) to the largest (fully painted), rounded to the nearest code, ties to even. CFA sequence auto-debayer can change the decoded detection input to RGB, but the mask remains grayscale.
• The new mask is named <target> - STARMASK; snapshots use <target> - Star Mask - SNAPSHOT. No file is saved automatically.
• The mask keeps the target's acquisition record, astrometric solution, and lineage, but none of the target's FITS/XISF header cards: it carries only the processing-state cards, ANLIN nonlinear, ANASRC process, and ANOP star-mask. Every sample is marked valid, and no linear encoding is claimed. Apply adds a lineage entry naming an::paintShapedStarMask, or an::paintEllipticalStarMask without Shaped Areas, with the step description.
• The new view's history starts with the step description. At the defaults it reads:

Created in shaped areas mode. Radius: 5, Threshold: 1.00, Profile: Gaussian. Percent Increase: 0.50, Pixel Increase: 0, Min Size: 2, Max Size: 25, Star Shape: Truncated Bell

Without Shaped Areas it says binary areas mode; with Use Lightness the profile is followed by , on the lightness. The target's own history is unchanged. - Snapshots hold what the Preview showed and do not gain the lineage entry that Apply records. - An active source mask and inversion state are ignored. Assign the generated mask later through the Masks workflow. - Nothing is stored between openings of the window.

Performance

Detection scales with image area and candidate count. The candidate scan runs in parallel bands, and every candidate is fitted with a nonlinear PSF, brightest first, until 20,000 stars are accepted or the candidates run out. Moffat, larger Radius, lower Threshold, higher Convergence, Relax PSF Checks, and dense fields increase work. Painting runs in parallel over rows, each row checking every accepted star, and each shaped star covers a square of 6R pixels on a side; solid ellipses sample every covered pixel on a sub-pixel lattice. A run copies the target (plus a floating working copy for integer images, and a lightness plane with Use Lightness), and holds the mask with, for an integer target, its floating working copy. A run the session's memory budget cannot hold is refused with the reason. Sequence processing adds decoding, encoding, and temporary disk proportional to frame count. Tune on Preview area, then verify the full frame before Apply. No production timing or peak memory was measured.

Worked example

• Evidence mode: Source-and-synthetic-test-derived.
• Input and settings: A synthetic linear grayscale Float32 field of planted stars, wide enough for the search, at the dialog defaults: Radius 5, Threshold 1.00, Gaussian, Shaped Areas, 0.50 Percent Increase, 0 Pixel Increase, size 2..25, and Truncated Bell.
• Expected checkpoint: The mask is one channel, the pixel under every planted star holds more than 0.5, and the shaped falloffs leave samples between 0 and 1. With Shaped Areas unchecked, every mask sample is exactly 0 or 1. On an RGB copy whose green channel holds the field and whose red and blue channels hold it mirrored, every green star is painted. A 32 × 24 pixel picture is refused at Radius 5, because it needs more than 28 pixels each way, and is searched at Radius 3, which needs more than 20.
• Inspect: At 100%, check missed peaks, false noise/hot pixels, saturation, blends, profile edges, and whether mask coverage reaches the intended wings.
• Limitation: This review did not execute an approved astronomical star field or sequence, so detection completeness, production mask quality, timing, and memory are not claimed.

Warnings and limitations

• Percent Increase is a multiplier, not an additive percent. Default 0.50 shrinks the measured base radius before additive pixels.
• Min/Max Size are diameter-like tests (2 x the larger FWHM), despite tooltips referring to star radius. They are ignored when Shaped Areas is unchecked.
• Shaped masks discard fitted ellipticity and angle by using the larger FWHM as a circular radius. Use solid ellipses when fitted ellipse geometry matters.
• Solid ellipses have hard edges and offer no soften control in this process; Percent Increase, Pixel Increase, Min/Max Size, and Star Shape do not apply to them.
• The Quadratic profile is fourth-power in the current implementation.
• A floating-point image is read as it is and full scale is taken as 1. The detector judges saturation as a fraction of the range from the sky to 1, so data scaled far above 1 is judged against the wrong range.
• Apply marks the mask nonlinear. Do not interpret its state as the source image's processing state.

Troubleshooting

Symptom or exact error	Verified cause/validation path	Recovery	Evidence source
Process is disabled or does not open	No active image/sequence, duplicate attached process, or exclusive attached process	Activate the intended view and close conflicting process windows	launchSingleImageProcess; registry descriptor
Error message includes the searched rectangle is too small for the search radius, at Preview or Apply	The picture, or the Preview area, is not more than 4 x Radius + 8 pixels wide and tall	Lower Radius, enlarge the Preview area, or uncheck it; nothing was made	an::planStarDetection
Error message includes the amplitude window's upper bound is at or above its lower bound	Amplitude Range Maximum is below its Minimum	Raise Maximum or lower Minimum	an::planStarDetection
Error message includes the largest roundness lies within the unit interval and at or above the smallest	Roundness Range Maximum is below Roundness Threshold	Raise Maximum or lower Roundness Threshold	an::planStarDetection
Error message includes the size window is finite, not negative and ordered	Min Size is above Max Size with Shaped Areas on	Correct the size bounds	an::paintShapedStarMask
Error at Preview or Apply on a camera mosaic	The image is a filter-array mosaic that has not been demosaiced	Demosaic first, or enable sequence auto-debayer	an::StarFrameView::create; an::planStarDetection
No stars appear	Threshold too high, Radius unsuitable, optional ranges reject all fits, or the searched plane is weak	Reset; check green versus Use Lightness; tune detection before size/growth; disable optional ranges	Process and detector sources
Many hot pixels/noise peaks appear	Threshold/size rejection is too permissive or Relax PSF Checks admits poor candidates	Raise Threshold; use shaped Min Size; disable Relax; inspect on the same display stretch	Detector rejection source
Moffat detects far fewer stars	Fits fail or beta falls below Minimum Beta	Return to Gaussian; use Moffat only for diagnosed wings and tune Convergence/beta carefully	an::detectStars rejection reasons
Mask is too small at Percent Increase 0.50	0.50 is a half-radius multiplier, not a 50% addition	Increase toward 1.0 and/or add Pixel Increase	an::paintShapedStarMask
Min/Max Size changes do nothing	Shaped Areas is unchecked	Re-enable Shaped Areas or accept that solid ellipses ignore shaped controls	StarMaskProcess::executeTypedProcessImpl
Shaped mask loses elongation	Shaped masks use the larger FWHM as a circular radius	Use solid ellipses to retain fitted ratio/angle, or use a later morphology workflow	an::paintShapedStarMask
Preview differs from final output	Preview area is searched on its own, or the display mode differs from the full-frame comparison	Uncheck Preview area, match Linear/Autostretch settings, and recheck at 100%	ImageRTPreviewControl preview path
Error names the memory budget	The session cannot hold the run's copies of the image and the mask	Close other images or work on a smaller crop; nothing was made	process_utils::normalizedCopyOf; process_utils::createDerivedImage
The mask has no OBJECT, filter, or exposure cards	A mask carries only the processing-state cards of its target's header	Expected; the acquisition record and astrometric solution are kept	process_utils::derivedImageMetadata

Related workflow steps

Use Star Profiler when you need a saved, inspectable, and manually curated detection list. Assign the output through Masks, refine it with Morphological Transformation, or use it to guide Star Reduction. For neural star separation instead of profile detection, use Starnet++.

References and provenance

• The fitted-PSF detector is adapted from Siril's star finder and PSF fit, by Francois Meyer and team free-astro (GPL-3.0-or-later), and extended by AfterNight.
• The six Star Shape profiles, their reach of three radii and the largest value kept where stars overlap are adapted from DeepSkyStacker's star-mask shapes, under the BSD 3-Clause License of Luc Coiffier and the DeepSkyStacker contributors. Help > About AfterNight credits both works and reproduces that licence's notice.
• AfterNight project source is authoritative for the detection plane, the threshold, the rejection windows, the size and growth rules, the solid-ellipse rule, representation/metadata/state behavior, and the Preview and sequence workflow.
• The generated mask is intended for AfterNight's standard image-mask system; see Masks for assignment and blend direction.