FITS Multi-Extension — Empty Primary plus SCI and MASK (.fits)
A three-HDU FITS file whose primary unit is header-only (NAXIS = 0) with the real data in named SCI and MASK extensions. A reader that only ever looks at HDU 0 reports an empty file, which is exactly the bug this fixture is built to catch.
| HDU | Type | EXTNAME | Shape | Contents |
|---|---|---|---|---|
| 0 | PRIMARY | - | NAXIS = 0 | header only, no data unit at all |
| 1 | IMAGE | SCI | 16 x 24 float32 | science array in Jy/beam |
| 2 | IMAGE | MASK | 16 x 24 uint8 | 85 pixels flagged where SCI > 400 |
Specifications
- Hdus
- 3
- Primary Naxis
- 0
- Extensions
- SCI (float32), MASK (uint8)
- Extnames
- SCI, MASK
- Flagged Pixels
- 85
- Total Pixels
- 384
Testing contract
Expected to pass- Scenario
- Enumerate the HDUs, then fetch the extension named SCI and the extension named MASK by name rather than by index.
- Expected result
- Three HDUs are reported, the primary has no data array, SCI is (16, 24) float32 and MASK is (16, 24) uint8 with exactly 85 non-zero flags.
What is a .fits file?
FITS (.fits, Flexible Image Transport System) is the standard binary format in astronomy. It pairs human-readable 80-character header cards (in 2880-byte blocks) with binary image or table data, storing pixel arrays, coordinates, and instrument metadata. It has been the astronomical archive format for decades.
How to use this file
Use an example .fits file to test FITS readers (astropy, CFITSIO, DS9), header-card parsing, and image or table extraction, or to verify block-alignment handling.
How to use this file for testing
“FITS Multi-Extension — Empty Primary plus SCI and MASK (.fits)” is a deterministic Novus Examples fixture for Scientific data, Serialization testing. Citation catalogs (BibTeX, RIS), chemistry structures (MDL Molfile, PDB), and gridded binary data (NetCDF, FITS) — for testing reference managers, molecule viewers, and scientific-data loaders.
Documented properties for this file: FITS · 14,400 bytes. Compare results against paired or grouped companions on this page when present (clean↔damaged, searchable↔scanned, or format twins) so scores stay reproducible across runs.
Download the file once, keep the path stable in CI or local scripts, and treat the spec table as the contract: dimensions, seeds, field lists, and roles are intentional. Corrupt or invalid samples are labelled as such — expect parsers to fail loudly rather than silently accept them.
Scientific fixtures are small, valid, and fully synthetic — no real organism, patient, sample, or observation. Point your parser or loader at the file and check it reads the documented records, variables, or headers; binary formats ship a readable twin or metadata listing for comparison.
Related files
- fitsFITS BLANK — Undefined Integer Pixels (.fits)Integer FITS images mark undefined pixels with the BLANK keyword, and BLANK is compared against the stored value before BZERO and BSCALE are applied. Scale first and the four undefined pixels turn into a perfectly plausible zero, which is the ordering bug this file exists to expose.
- fitsFITS Image — BITPIX 16 with BZERO Unsigned Trick (.fits)FITS has no unsigned 16-bit type, so unsigned data is stored signed with BZERO = 32768 and recovered as BZERO + BSCALE * stored. Every stored value in this image is negative, so a reader that ignores the scaling returns an entirely negative frame while parsing the file perfectly.
- fitsFITS Image — BITPIX 8 Unsigned Bytes (.fits)The baseline rung of the BITPIX ladder: a 24x16 synthetic star field stored as unsigned bytes, the one integer width FITS holds without a BZERO shift. Every image in this family carries the same scene so a decoder can be scored across data types.
- fitsFITS Image — float32 with NaN and Inf Pixels (.fits)Single-precision FITS pixels including two NaNs, which is the only way the standard marks undefined data for floating BITPIX, plus one +Inf. Statistics computed without NaN-aware reductions come back as NaN for the entire frame.
- fitsFITS Image — float64 Double Precision (.fits)The top rung of the BITPIX ladder, carrying the identical synthetic scene as IEEE-754 doubles with DATAMIN and DATAMAX declared. It is the reference against which the 8-, 16- and 32-bit members of the family are scored for precision loss.
- fitsFITS with World Coordinate System — Tangent Plane (.fits)A 32-bit integer image carrying a complete tangent-plane WCS: 1-based CRPIX reference pixels, a deliberately negative CDELT1 so right ascension runs the other way, and an ICRS frame. It targets the two mistakes every WCS implementation makes first, the 1-based origin and the flipped axis.
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