# FITS Header & Image Inspector

> Read a FITS header, check BITPIX, scaling and Bayer keywords, and preview the image. Open an astronomical FITS file (also .fits.gz) to list every header card, see the data type, BZERO/BSCALE scaling, row order and Bayer pattern, measure per-plane statistics and download a stretched preview PNG. Reads the primary image or the first image extension; tile-compressed files are explained, not guessed. Lumina Astro Lab uses the same reader on your device.

Part of usefulweb.app (https://usefulweb.app/). Part of [Lumina](https://lumina.usefulweb.app/) (ownerApp: lumina). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://luminafitsinspector.usefulweb.app/ (interactive tool at https://luminafitsinspector.usefulweb.app/tool)
- JSON API: POST https://luminafitsinspector.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://luminafitsinspector.usefulweb.app/api/v1/tool)
- OpenAPI: https://luminafitsinspector.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://luminafitsinspector.usefulweb.app/mcp - tool `lumina_fits_inspector`

## Inputs
- file (file, required): FITS file (.fits, .fit, .fts or .gz; up to 16 MB)
- stretch (select): Preview stretch

## Method
- The header is parsed card by card (80 characters, keyword = value / comment) until END, following FITS Standard 4.0: strings with doubled quotes, logical T/F, integers and reals including D exponents. COMMENT and HISTORY cards are listed as text.
- Data are read big-endian for BITPIX 8, 16, 32, 64, −32 and −64 and converted to physical values with BZERO + BSCALE × stored value; BLANK integers become empty pixels. Two-dimensional images and cubes with three planes are supported. An empty primary array leads to the first IMAGE extension; tile-compressed (ZIMAGE) data and tables are rejected with an explanation.
- FITS stores the bottom row first; the preview is flipped to the usual orientation unless ROWORDER = TOP-DOWN. Statistics: min, max and mean over every pixel; median and MAD-based σ from up to one million evenly spaced samples. The preview is box-averaged to at most 1024 pixels per side and stretched for display only.