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How to open .FTS files on iOS

To open .FTS files on iOS, iOS may not preview FITS/FTS files in Quick Look; transfer the .FTS file to a desktop computer and open it with a FITS viewer (for example, one of the viewers listed on NASA’s FITS viewer page).

Step-by-step instructions

  1. iOS may not preview FITS/FTS files in Quick Look; transfer the .FTS file to a desktop computer and open it with a FITS viewer (for example, one of the viewers listed on NASA’s FITS viewer page).

Alternative methods

  • Open .FTS in a browser-based viewer if desktop apps fail.
  • Try opening .FTS on iOS with a secondary app to rule out app-specific issues.
  • Convert .FTS only with trusted tools when direct opening is not possible.

Common issues

The .FTS file won’t open or shows as an unknown format

Many default photo viewers do not support FITS/FTS, so the OS may not know which app to use.

  1. Open the file in a FITS-capable viewer (NASA’s FITS viewer page lists common FITS software, e.g., SAOImage DS9).
  2. If it still fails, confirm the file is actually a FITS file (FTS is commonly used for FITS, but the extension alone is not a guarantee).

The image looks blank, very dark, or has strange contrast

FITS pixel data often requires scientific scaling/stretching; it may not display well with default settings.

  1. In your FITS viewer, adjust display scaling/stretch (e.g., different autoscale options) to reveal faint detail.
  2. Check the header metadata and data type handling; some files contain high dynamic range or non-visual data arrays.

The file opens but metadata/headers look confusing

FITS headers use standardized keyword/value cards and can be extensive and technical.

  1. Use your FITS tool’s header viewer to inspect keywords and comments; this is the canonical metadata for the dataset.
  2. Refer to the FITS standard documentation for header structure and keyword conventions.

A program reports the FITS file is corrupted or non-compliant

Incomplete downloads, transfer issues, or non-standard writers can produce files that strict readers reject.

  1. Re-download or re-copy the file using a reliable method and verify it was fully transferred.
  2. Try opening with another FITS-capable tool/library (many software stacks use CFITSIO, which is widely used for FITS reading/writing).

Security note

FITS/FTS files are data files (not executable), but they should still be treated as untrusted input: malformed files can trigger bugs in complex image/data parsers. Prefer opening unknown .FTS files with well-maintained FITS tools.

Back to .FTS extension page