About FITS Files
FITS Astronomical Image
FITS (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.
Family
Raster & Vector Images
Extension
.fits
MIME Type
image/fits
Can Use As
46 49 54 53 00 01 00 00 4B 41 49 4A ASCII: FITS....KAIJ Tap to choose your file Drop files here or click to browse
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HOW FITS CAME TO BE.
FITS — Flexible Image Transport System — was designed in 1981 by Don Wells (NRAO), Eric Greisen (NRAO), and Ron Harten (Dwingeloo Observatory) as the standard astronomical data interchange format. The IAU formally endorsed it in 1982. A FITS file is astonishingly self-documenting: every file begins with an ASCII header listing every variable, unit, coordinate system, instrument, and observation timestamp. After the header come 2D, 3D, or N-dimensional data arrays at whatever precision the telescope captured.
Every major telescope on Earth and in orbit produces FITS. Hubble, JWST, Chandra, the Very Large Telescope, every CCD-equipped backyard astronomer — all write FITS. NASA’s public Hubble archive holds over 2 million FITS files, available for anyone to download. The format is older than TCP/IP and still the backbone of astronomy in 2026. Wells’ deliberate design choice — keep the format simple, text-headered, and forever stable — is widely cited as a triumph of scientific data stewardship.
Technical Specifications
- MIME type
- image/fits
- 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
Typical Sizes & Weights
Backyard-telescope CCD shot (5 MP)
10-30 MB
Hubble WFC3 single exposure
~65 MB
JWST NIRCam full detector
~650 MB
STRENGTHS & LIMITATIONS.
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.
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.
CURIOSITIES & TRIVIA.
Every raw image from the Hubble, James Webb, Chandra, and essentially every professional telescope is a FITS file.
FITS was ratified in 1982 and has maintained complete backward compatibility — files from 1982 open identically in 2026 software.
NASA's Mikulski Archive for Space Telescopes (MAST) holds over 2 million public Hubble FITS files free to download.
FITS headers are ASCII text with 80-character records — you can open a FITS in Notepad and read the observation's metadata directly.
The format can hold images, spectra, binary tables, and any n-dimensional array — one container for astronomy's entire data spectrum.
Specialized Utilities for .FITS Files
Compress Image to 20KB
Compress signature scans, stamp images, and ID photos to strictly ≤ 20 KB (20,000 bytes) for strict online exam and government application portals using binary-search JPEG quantization. Executes isolated compress processing via imagemagick (COMPRESS (imagemagick): Isolated compress pipeline via imagemagick with SHA-256 verification) with deterministic output verification and automatic 60-minute GDPR file deletion.
Compress Image to 50KB
Compress JPG, PNG, or WebP photos to strictly under 50 KB (50,000 bytes) for passport portals, university admissions, civil service forms, and KYC uploads without changing pixel dimensions. Executes isolated compress processing via imagemagick (COMPRESS (imagemagick): Isolated compress pipeline via imagemagick with SHA-256 verification) with deterministic output verification and automatic 60-minute GDPR file deletion.
Compress JPG to 100 KB
Upload a JPG and download a decodable JPG at or below 100,000 bytes. If the limit cannot be reached, no output is offered. Executes isolated compress processing via imagemagick (COMPRESS (imagemagick): Isolated compress pipeline via imagemagick with SHA-256 verification) with deterministic output verification and automatic 60-minute GDPR file deletion.
Crop Image & Photo Resizer
Crop and resize JPG, PNG, WEBP, and AVIF images to exact pixel dimensions, social media aspect ratios, or custom print DPI online for free. Executes isolated resize processing via imagemagick (RESIZE (imagemagick): Isolated resize pipeline via imagemagick with SHA-256 verification) with deterministic output verification and automatic 60-minute GDPR file deletion.
Resize Image
Resize images to exact dimensions or scale by percentage. Lock aspect ratio to prevent distortion. Supports all common image formats. Executes isolated resize processing via (RESIZE (): Isolated resize pipeline via with SHA-256 verification) with deterministic output verification and automatic 60-minute GDPR file deletion.
PNG Compressor — Reduce PNG Size Preserving Transparency
Compress PNG images up to 80% while preserving full alpha-channel transparency, or lock exact file size targets (20 KB, 50 KB, 100 KB). Executes isolated compress processing via imagemagick (COMPRESS (imagemagick): Isolated compress pipeline via imagemagick with SHA-256 verification) with deterministic output verification and automatic 60-minute GDPR file deletion.
WEBP Compressor — Optimize WebP for Core Web Vitals
Compress WEBP images for ultra-fast page loads and Lighthouse scores with fine-grained quality sliders and exact byte targets. Executes isolated compress processing via imagemagick (COMPRESS (imagemagick): Isolated compress pipeline via imagemagick with SHA-256 verification) with deterministic output verification and automatic 60-minute GDPR file deletion.
Favicon Generator — Multi-Resolution .ICO from PNG, SVG or WEBP
Generate a production-ready multi-resolution favicon.ico containing 16x16, 32x32, 48x48, 64x64, 128x128, and 256x256 alpha layers from any logo. Generates multi-resolution ICO containers (16×16, 32×32, 48×48), Apple Touch icons (180×180), and PWA manifest PNGs from a single source graphic with crisp alpha-channel anti-aliasing.
EXIF Metadata Remover
Strip hidden GPS coordinates, camera serial numbers, timestamps, and XMP/IPTC metadata from JPG, PNG, WebP, and TIFF photos before sharing online. Strips sensitive EXIF camera serials, GPS coordinates, IPTC copyright blocks, and XMP editing history from JPEG, PNG, WebP, and HEIC images after normalizing physical orientation flags.
Image to Text (OCR)
Extract text from images using optical character recognition. Supports photos of documents, screenshots, receipts, and handwritten notes in 100+ languages. Executes isolated ocr processing via (OCR (): Isolated ocr pipeline via with SHA-256 verification) with deterministic output verification and automatic 60-minute GDPR file deletion.
JPG to Word Converter (OCR)
Convert scanned JPG, PNG, and WEBP images into editable Microsoft Word (DOCX) documents using 12-language optical character recognition (OCR). Executes isolated convert processing via pandoc (CONVERT (pandoc): Isolated convert pipeline via pandoc with SHA-256 verification) with deterministic output verification and automatic 60-minute GDPR file deletion.
Common Use Cases
Primary production use cases for .FITS (FITS Astronomical Image) center on Raster & Vector Images pipelines requiring [MIME type: image/fits · 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]. 1) Self-documenting — every file carries complete observational metadata. 2) Lossless — bit-exact storage of detector readouts. 3) Capacity planning and delivery optimization across standard footprints (Backyard-telescope CCD shot (5 MP) → 10-30 MB; Hubble WFC3 single exposure → ~65 MB; JWST NIRCam full detector → ~650 MB), with direct interoperability across PDF, PNG, MP4 via imagemagick.
FITS — Limitations
Known technical limitations and troubleshooting for .FITS (FITS Astronomical Image): 1) Niche — used almost exclusively in astronomy. 2) File sizes are large (no default compression). 3) When software or upload portals reject image/fits streams due to profile mismatches (MIME type: image/fits · 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), converting .FITS to PDF, PNG, MP4 on KaijuConverter normalizes headers, color/audio streams, and metadata with automatic 60-minute GDPR cleanup.
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.
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.
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.
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