[KnifeLemon]

Filee reads FITS pictures (.fits, .fts) from telescope cameras and capture/stacking programs, as planned in #460. .fit is not claimed: it stays free for Garmin FIT (#451).

What it does

Reading (Magick/Fits.cs, written from the FITS 4.0 standard, no new dependency)

• 2880-byte blocks of 80-character header cards, big-endian data, BITPIX 8 / 16 / 32 / 64 / -32 / -64, physical values = BZERO + BSCALE × stored (BLANK integers become undefined).
• The primary HDU or, when it is empty, the first IMAGE extension. A cube with NAXIS3 = 3 is red, green and blue; other cubes give their first plane.
• Bayer pattern from BAYERPAT, else COLORTYP (RGGB, BGGR, GRBG, GBRG; case and padding ignored), at the first stored pixel and shifted by XBAYROFF / YBAYROFF. Keywords missing from an extension are looked up in the primary header.
• ROWORDER = 'BOTTOM-UP' turns the picture upright. Without it, rows are taken top-down, as capture programs write them.
• Tile-compressed files (fpack, a BINTABLE with ZIMAGE = T) fail with a message asking to funpack them. Damaged or cut-short files fail with a reason.

FITS → PNG / JPG (and every other picture target) (Magick/FitsRendering.cs)

• Automatic stretch, like a capture program's preview: values scaled to 0–1 over their range; per channel, shadows clipped 2.8 normalized MADs below the median, then a midtones transfer function takes the median to 0.2.
• A colour camera's mosaic is debayered first (bilinear) with the header's pattern. A new preset option, Debayer FITS from a colour camera (on by default), keeps it mono when turned off. Channels are stretched one by one, so the sky comes out neutral. Mono files and three-plane colour files are never debayered.
• The result is 8-bit and then goes through ImageMagick as usual (resize, rotate, quality, …). PDF, ICNS, HEIC and SVG are reached the same way.

FITS → TIFF (Magick/TiffWriter.cs, our own small baseline TIFF writer, because the Q8 ImageMagick stores only 8 bits)

• New preset option FITS (astronomy) to TIFF: Linear: the data as it is (default) or Stretched, like a preview.
• The TIFF follows the file's BITPIX: 8-bit stays 8-bit and 16-bit stays 16-bit (BZERO/BSCALE applied, so unsigned 16-bit comes out as unsigned 16-bit). 32-bit integer and floating-point data (BITPIX 32, 64, -32, -64), and 8/16-bit data that doesn't fit the unsigned range (negative or scaled values), become 32-bit floating point, so nothing is cut.
• Never debayered: the mosaic stays intact for the program that processes it.
• Uncompressed, LZW or Deflate, following the preset's TIFF compression (integer data uses the horizontal predictor). Rotate and flip apply. Resizing and the other picture options don't.
• FITS → TIFF costs 11 instead of 10, so other targets are always reached through the stretched picture and never through the linear TIFF.

Settings and UI

• ImageOptions.FitsTiff (lenient enum) and ImageOptions.FitsDebayer (default true; presets saved before this read as linear TIFF and debayer). Both are shown in the preset editor's image card: the TIFF choice for TIFF targets, the checkbox for the other picture targets.
• Settings schema 43 teaches the images donut .fits and .fts without taking them from a donut of the user's. Schema 42 is the print studio from feat(spreadsheet): preview and edit XLSX page layout before PDF export #437.
• The six new strings are translated in all 14 language files (Korean in 해요체).
• Docs: docs/ENGINES.md (table row and a FITS section), and the 13 READMEs (FITS in the images row, 255 → 256 formats).

What it doesn't do

• No 16-bit PNG: the bundled ImageMagick is Q8, so PNG/JPG are 8-bit and stretched.
• No tile-compressed (fpack .fz) or table-only FITS. No data cubes beyond three colour planes (the first plane is taken).
• No debayering in the TIFF, and no CFA tags in it. No FITS header copied into the TIFF.
• A linear float TIFF keeps the values as they are. ADU-range floats (for example 0–65535) look white in viewers that expect 0–1.
• The stretch is median/MAD based like N.I.N.A.'s preview, with similar defaults (−2.8, 0.2), but it is not guaranteed to match it pixel for pixel. It is unlinked (per channel) for colour.
• Row order: without a ROWORDER keyword, files are taken as top-down (what N.I.N.A., MaxIm DL and similar capture programs write; PixInsight's default view). DS9-style bottom-up viewers would show such a file flipped. The Bayer pattern is read at the first stored pixel.
• The interactive Crop tool still reads through ImageMagick directly (as it does for DICOM).

Tests

• tests/Filee.Engines.Tests/FitsTests.cs (25 tests; FITS and TIFF files are generated in the tests):
  • BITPIX 8, 16 with BZERO 32768, 32, -32 and -64 into linear TIFF, checked sample by sample.
  • Signed 16-bit with negative values, written as float.
  • LZW and Deflate TIFFs read back by libtiff, including LZW strips of random data that reset the code table.
  • A stretched 16-bit TIFF and a stretched mono PNG.
  • An RGGB mosaic debayered with each of the four patterns, the offsets and COLORTYP; the same mosaic kept mono; the linear TIFF keeping it.
  • A three-plane colour file, ROWORDER, rotation of a TIFF, header parsing (D exponents, quoted strings, repeated keywords), an IMAGE extension, fpack / not-FITS / truncated files, the stretch math, and the routes (FITS → PDF never via TIFF).
• tests/Filee.Core.Tests/FitsFormatTests.cs: extension detection (.fit is not FITS), the images donut, the schema 43 migration keeping a custom claim, and old/new preset JSON.
• RenderTests.Preset_editor_shows_and_saves_the_fits_options (en, ko).
• Local results: Core 546 passed; Engines FITS plus the image, PDF, tracing, DICOM, multi-page TIFF and JPEG XR suites, 132 passed; App Localization + Preset, 168 passed. dotnet format --verify-no-changes is clean.
• Release timing on a 6248 × 4176 Bayer frame: TIFF about 1.2 s; PNG about 8 s, mostly ImageMagick's PNG encoder.

Closes #460

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