Calibration Libraries

You can catalog bias, dark, dark-flat, and flat frames alongside the lights they serve. PSF Guard matches them conservatively, builds master frames only when they are needed for a stack, and keeps the raw frames and generated FITS files on disk.

Calibrate

You can add calibration folders to the same catalog as your lights.

The import process reads file headers, and stack previews build and cache safe masters on demand.

You can add frames below ↓

You can add calibration frames to the catalog.

In Settings → Databases, add the folders holding the calibration files to the catalog's image directories.
Choose Import, select Calibration only when appropriate, and inspect the dry preview before applying it. New-database creation and the CLI use the same header-only scan.
Open the database's calibration summary and choose Manage to inspect coverage by rig and frame type.

PSF Guard recognizes the usual IMAGETYP values:

Library type	Recognized header values
Bias	`BIAS`, `OFFSET`
Dark	`DARK`
Dark flat	`DARK FLAT`, `DARKFLAT`, `FLATDARK`
Flat	`FLAT`

Calibration records stay in PSF Guard-owned tables inside the catalog. Pixels and master blobs do not: raw paths and file fingerprints point back to the image library, while generated masters live in the cache. Reading an untouched Target Scheduler database does not create the calibration tables, and a dry run rolls its temporary catalog changes back.

You can manage imaging rigs and calibration libraries.

A stable rig identity combines telescope, camera, sensor dimensions, and binning; N.I.N.A. profile IDs are recorded separately. A copied database therefore carries the calibration catalog without tying it to one local row number or profile.

The library manager filters by rig and frame type, marks paths that no longer exist, and shows the settings used for matching. An editor with database management enabled can rescan the configured folders, forget a bad catalog record without deleting its file, or clear generated masters while retaining all raw frames. Forgetting an input invalidates every dependent master automatically.

You can check calibration coverage for each project.

Choose Calibration on a project card in Overview. The report uses the same matcher as a real stack, so it shows what would apply rather than merely counting files in the library.

Each frame type shows its matching frames, capture sessions, and newest date. For each light night and filter, the report shows the selected flat session, its age, and whether it came from the same night. Warnings list missing frame types, stale flats, nights without matching flats, and light files that PSF Guard could not find.

Calibration coverage report with matching bias, dark, and flat counts for each light night and filter — The report uses the stack matcher, so the counts show which calibration frames PSF Guard would use.

The matching system uses conservative settings to match frames.

A calibration frame must match every known required setting. If the light records a value but the calibration frame does not, they do not match. Frames without a known sensor identity never match. PSF Guard orders safe matches by capture-time distance and uses at most 64 inputs for one master.

Master	Required agreement
Bias	Camera, dimensions, channels, binning, gain, offset, readout mode, and Bayer layout
Dark	Bias fields, exposure within the larger of 0.1% or 0.05 seconds, and temperature within 3 °C
Dark flat	Flat sensor settings, exposure, and temperature
Flat	Bias fields, filter, telescope, focal length within 1 mm, and rotator angle within 1° when both frames record it

Frames used for one master must also match one another. Temperatures must stay within 1 °C, and flats must come from one capture session. PSF Guard selects the nearest consistent group and ignores an outlier instead of rejecting an otherwise usable group.

Before building the master, Seiza checks the inputs again. It skips frames with the wrong filter, camera, gain, or readout mode. The warning identifies the skipped frame type and count. The remaining safe inputs can still build the master.

The stack panel provides three calibration modes.

The stack panel's Calibration control has three modes:

Mode	Behavior
Auto	Default. Apply only masters whose matching and dependency chain are safe.
Force on	Use every master that can be built, including a flat without a trusted pedestal estimate; the card warns about the risk.
Off	Skip matching and integrate the raw lights.

The project-level choice is saved, and you can override it on individual target and filter cards. You can disable calibration for a single channel without discarding calibration for the remaining channels. Results built under a different mode are marked as outdated.

Multi-night stacks may need different flats or darks. PSF Guard partitions the lights into calibration sessions, swaps the appropriate masters as it integrates each group, and reports the session count on the card. Resume checkpoints and source-artifact searches include the exact per-session master identity, so changed calibration always forces the safe amount of rebuilding.

A master that fails to build does not fail the stack. The affected lights continue without it, and the card names the skipped master and full reason. A dependent master is skipped rather than built from a failed input.

The system applies flat-field safeguards and pedestal estimation.

A flat divides correctly only after the light's pedestal is removed. A bias or dark master provides that subtraction. With a flats-only library, PSF Guard can fit the pedestal from the lights when the field provides enough vignetting and the estimate passes consistency guardrails. The card reports the fitted value; an untrustworthy fit leaves the flat unused in Auto mode and explains why.

Flat masters receive a spatial defect pass because a hot pixel repeats in every flat and survives across-frame clipping. Darks retain their hot pixels so they can subtract the lights' own. If no dark master exists, calibrated lights receive the same impulse filter before integration.

You should let stars move between sky flats. You can dither or let the sky drift during capture. Tracking a star on the same flat pixels allows it to survive statistical clipping, and star profiles are too wide for the pixel-defect filter to remove.

The system caches generated masters with full provenance details.

Each master needs at least two inputs. Seiza uses a two-pass, leave-one-out sigma-clipped mean and writes the input count and clipping provenance into the FITS. Cached filenames are content-addressed from the input frame identities and fingerprints, dependency masters, and processing versions. Changing a bias invalidates dark and flat masters that used it; a valid unchanged master is reused.

<cache>/<database>/calibration-masters/

You can export lights along with their calibration frames.

Project and target exports add the raw calibration frames safely matched to each selected light. The default target-grouped layout keeps flats beside the target they serve. The optional WBPP layout uses PixInsight's frame-type roots, puts dark flats beside darks, and includes run-wbpp.sh and run-wbpp.cmd to load the export into WeightedBatchPreprocessing.

You can open the Export for Stacking guide to review export procedures. This guide covers both directory structures, UI and CLI controls, the generated WBPP handoff, and repeat-export behavior.

You can copy calibration records when moving a catalog.

Merge catalogs and sync pull copy rigs, profile bindings, and raw calibration-frame records. They intentionally do not copy generated master rows or cached FITS files. The destination resolves stale raw paths by basename under its own configured image folders and builds its own masters.

Use this troubleshooting table to resolve calibration issues.

Symptom	Check
No calibration summary	You should add the calibration folder to the catalog, run the import process, and confirm that the `IMAGETYP` header correctly identifies the frame.
No matching master	You should verify the camera, size, binning, gain, offset, readout mode, exposure, temperature, filter, telescope, focal length, and recorded rotator angle settings match between frames.
Master build warning	You can open the card details to view the skipped master and its cause. The light stack continues using the masters that built successfully.
Flat makes edges brighter	You should use Auto mode and import bias or dark frames. Force on mode can apply a flat whose pedestal was not removed.
Stars in a sky-flat master	You can dither or allow drift between flats, as stars in a fixed position cannot be removed by clipping.
Old master reused	Changed input fingerprints invalidate the master automatically. You should use the Clear masters command only when you need to rebuild every valid master.