# AstroFileViewer — FITS and XISF Viewer

> View and process astronomical image files (FITS, XISF) on iOS devices. (iPhone/iPad app by Joerg Klaas.)

- Source: https://appshunter.io/ios/app/astrofileviewer/id6760240080 (this page in markdown: same URL + `.md`)
- Developer: [Joerg Klaas](https://appshunter.io/developer/1879846001)
- Category: Photo & Video, Utilities
- Price: Free
- Rating: 5.00/5 from 1 App Store ratings · 1 written reviews indexed
- Age rating: 4+
- Requires: iOS 16.4 · 1 MB
- Languages: American English
- Released: 2026-03-12
- Data updated: 2026-08-06
- Monetization: free
- User reviews in markdown: https://appshunter.io/ios/app/astrofileviewer/id6760240080/reviews.md

## What is AstroFileViewer?

AstroFileViewer lets you open and view astronomical image files (FITS and XISF) directly on your iPhone or iPad. Whether you receive a sub-exposure via AirDrop, download one from Safari, or browse your imaging files in the
  Files app — AstroFileViewer displays them with a proper PixInsight-compatible STF auto-stretch so you can actually see what's in your data.

  Why stretching, gradient control and denoising on an iPhone?
  Simple. You get an early impression of how your data could look after post-processing. And it's simply fun too.

  Features:

  - Open FITS and XISF files from Files, Safari, AirDrop, email, Google Drive, or any share sheet
  - PixInsight-compatible Screen Transfer Function (STF) auto-stretch for proper visualization of linear astronomical data
  - Supports mono and RGB images from all major astro cameras, including OSC debayer (RGGB, GRBG, GBRG, BGGR)
  - Dark point slider — clip noisy backgrounds, just like AstroBlink on macOS
  - Contrast slider — S-curve with logarithmic response for fine control
  - Color saturation slider — boost Ha reds and OIII blues in your OSC data
  - GPU bilateral denoise — edge-preserving noise reduction, up to 300% strength
  - Gradient correction — auto-detects and removes linear light pollution gradients
  - Auto-rotate — landscape images automatically fill your screen in portrait mode
  - File history with swipe navigation — swipe left/right to flip through recently opened files, even after restarting the app
  - Recent files on start screen — thumbnail grid of your last 6 images for quick access
  - Tap-to-fullscreen — single tap hides all UI for distraction-free viewing
  - Pinch-to-zoom up to 10x with smooth panning
  - SNR and star count shown in the status bar
  - FITS/XISF header inspector — view all keywords with important ones highlighted
  - Save to Photos as a stretched JPEG with all adjustments baked in
  - Full compression support: LZ4, LZ4HC, zlib, zstd, fpack (Rice, GZIP), ByteShuffle
  - Persistent settings — all sliders and toggles remembered between sessions
  - Built-in help section — tap the ? icon anytime
  - All processing happens on the GPU. All sliders respond in real-time.

  AstroFileViewer registers as a handler for .xisf, .fits, .fit, and .fts files on your device.

  No account required. No internet connection needed. Your files stay on your device.
  Built by an astrophotographer, for astrophotographers.

## Key features

- Open FITS and XISF files from various sources
- PixInsight-compatible STF auto-stretch
- Mono and RGB image support with OSC debayer
- Dark point and contrast sliders
- Color saturation adjustment
- GPU bilateral denoise
- Gradient correction

## Recent user reviews (1 of 1)

All indexed reviews: https://appshunter.io/ios/app/astrofileviewer/id6760240080/reviews.md

### 5/5 — Great App for Astrphotographers

*2026-04-10*

This is an app that I've been waiting for. Gives the ability to open and edit astro image files in the professional FITS format. Very fast with great editing tools.

**Developer response:** 🙏🏻👍🏻

## Frequently asked questions about AstroFileViewer

### What file formats does AstroFileViewer support?

AstroFileViewer supports FITS and XISF files, which are common formats in astrophotography. It can also handle compressed versions like LZ4, zlib, and zstd.

### Does AstroFileViewer have ads?

No, AstroFileViewer does not contain advertisements. It is a completely free application designed for astrophotographers.

### Can I edit my astronomical images with AstroFileViewer?

Yes, AstroFileViewer offers several editing features. You can adjust dark point, contrast, and color saturation, as well as apply GPU-accelerated denoising and gradient correction.

### What devices is AstroFileViewer compatible with?

AstroFileViewer is designed for Apple devices and is compatible with both iPhone and iPad.

### How does AstroFileViewer handle image stretching?

It uses a PixInsight-compatible Screen Transfer Function (STF) auto-stretch to properly visualize linear astronomical data, making faint details visible.

### Is AstroFileViewer suitable for beginners in astrophotography?

While built by an astrophotographer, the app's features like auto-stretch and gradient correction can be very helpful for beginners to quickly assess their data quality.

### How often is AstroFileViewer updated?

The latest version, 1.5.0, was released on May 3, 2026, indicating recent development activity. Updates typically bring new features and improvements.

### Can I save my processed images from AstroFileViewer?

Yes, you can save your adjusted images as stretched JPEGs directly to your Photos app, with all your applied adjustments baked in.

## Version history (last 5 releases)

### 1.5.0 — 2026-05-03

Now with TIFF Support

### 1.4.1 — 2026-04-03

Fixed an issue with pre processed or stacked files from e.g. AstroPixelProcessor

### 1.4.0 — 2026-03-23

What's New (v1.4.0):

  - Dark point slider — clip faint background noise
  - Contrast & saturation sliders — S-curve contrast, color boost for OSC
  - GPU bilateral denoise — up to 300%
  - Gradient correction — auto LP removal, up to 300%
  - Auto-rotate landscape images to portrait
  - File history — swipe between recent files, thumbnail grid on start screen
  - Tap-to-fullscreen immersive mode
  - SNR & star count in status bar
  - Logarithmic contrast curve for usable full-range control
  - Home button to return to start screen
  - Swipeable slider panel
  - Performance: cached STF params, stats computed once per image
  - Fix: Bayer pattern detection now case-insensitive
  - Fix: file opening from share sheet reliability

### 1.3.2 — 2026-03-13

Fixed FITS UTI org.fits.fits → gov.nasa.gsfc.fits
and inserted trilinear filter to avoid moire effects.

### 1.3 — 2026-03-12

No release notes.

## More apps by Joerg Klaas

- [Atempause](https://appshunter.io/ios/app/atempause/id6759622605)

All apps by Joerg Klaas: https://appshunter.io/developer/1879846001

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-08-06.*