FITS vs PDF
A detailed comparison of FITS Astronomical Image and PDF Document — file size, quality, compatibility, and which format to choose for your workflow.
FITS Astronomical Image
Raster & Vector ImagesFITS (Flexible Image Transport System) is the standard digital file format in astronomy for storing images, tables, and metadata from telescopes and satellites. It supports multi-dimensional arrays and extensive header metadata for scientific observation records.
About FITS filesPDF Document
Documents & TextPDF is the universal standard for sharing documents with consistent formatting across all devices and operating systems. It preserves fonts, images, and layout exactly as intended by the author.
About PDF filesStrengths Comparison
FITS Strengths
- Self-documenting — every file carries complete observational metadata.
- Lossless — bit-exact storage of detector readouts.
- Stable since 1981 with zero breaking changes.
- Mandatory for professional astronomy — every research publication uses it.
- Open standard endorsed by IAU.
PDF Strengths
- Pixel-perfect fidelity across operating systems, browsers, and printers.
- Embeds fonts, so documents render identically without the reader having them installed.
- Supports digital signatures, encryption, and redaction for legal workflows.
- ISO-standardized (ISO 32000) with multiple validated subsets (PDF/A, PDF/X, PDF/UA).
- Supports both vector and raster content, keeping line art crisp at any zoom level.
Limitations
FITS Limitations
- Niche — used almost exclusively in astronomy.
- File sizes are large (no default compression).
- Not a display format outside specialized viewers (DS9, AstroBin).
- Consumer imaging apps don't understand FITS.
PDF Limitations
- Editing is difficult — the format is optimized for display, not mutation.
- Text extraction can scramble reading order in multi-column layouts.
- File sizes balloon quickly when embedding high-resolution images or fonts.
- Accessibility (screen readers) requires careful tagging that many PDFs skip.
- JavaScript support has historically been a malware vector.
Technical Specifications
| Specification | FITS | |
|---|---|---|
| MIME type | image/fits | application/pdf |
| Extensions | .fits, .fit, .fts | — |
| Standard | IAU-endorsed FITS 4.0 (latest revision) | — |
| Header records | 80-character ASCII cards | — |
| Encoding | IEEE big-endian integers and floats | — |
| Current version | — | PDF 2.0 (ISO 32000-2:2020) |
| Compression | — | Flate, LZW, JBIG2, JPEG, JPEG 2000 |
| Max file size | — | ~10 GB (practical); 2^31 bytes (theoretical per object) |
| Color models | — | RGB, CMYK, Grayscale, Lab, DeviceN, ICC-based |
| Standard subsets | — | PDF/A, PDF/X, PDF/UA, PDF/E, PDF/VT |
Typical File Sizes
FITS
- Backyard-telescope CCD shot (5 MP) 10-30 MB
- Hubble WFC3 single exposure ~65 MB
- JWST NIRCam full detector ~650 MB
- 1-page text-only memo 50–150 KB
- 10-page report with images 500 KB – 2 MB
- Scanned document (per page) 100 KB – 1 MB
- Full-color magazine (48 pages) 10–40 MB
Ready to convert?
Convert between FITS and PDF online, free, and without installing anything. Encrypted upload, automatic deletion after 2 hours.
Frequently Asked Questions
FITS (FITS Astronomical Image) is an image format used to store raster graphics — a two-dimensional grid of pixels describing a picture. It is part of the raster & vector images family and designed around a specific trade-off between file size, visual fidelity, and feature support (transparency, colour depth, compression type). Photographers, web designers, and content creators choose FITS when its particular strengths match the publishing target.
PDF (Portable Document Format) was created by Adobe in 1993 to present documents consistently across all devices and operating systems. It preserves fonts, images, layouts, and formatting regardless of the software used to view it.
Most desktop photo viewers (Windows Photos, macOS Preview, GIMP, Photoshop, Affinity Photo) open FITS natively. On mobile, iOS Photos and Google Photos display FITS in the gallery when supported by the OS. If the format is rare or new, convert to JPG or PNG first — both are universally readable — using our FITS to JPG or FITS to PNG converter.
PDF files can be opened with Adobe Acrobat Reader (free), web browsers like Chrome and Edge, macOS Preview, and alternative readers like Foxit and Sumatra PDF.
Upload the FITS to KaijuConverter and pick a target format (JPG, PNG, WebP, HEIC, TIFF, BMP, SVG, PDF). The conversion runs in the browser via ImageMagick and returns a download in seconds. No account or installation required; both input and output delete automatically within two hours.
It depends on the task. JPG is the smallest file size for photographs; PNG is lossless with transparency; FITS has its own niche that may favour colour depth, animation, or encoding efficiency over one or both of those. For the final web publish, test all three and measure file size plus visible quality on real content.