RAW to FITS Converter

RAW to FITS Conversion Explained

Converting .RAW to .FITS transforms proprietary digital camera sensor data into the standard format used for astronomical processing. Astrophotographers and researchers perform this conversion to process images captured on consumer cameras using specialized scientific software.

When you convert raw to fits, you gain compatibility with math-heavy astronomical tools and a standardized header system for metadata. You lose proprietary camera metadata, such as manufacturer notes and lens profiles. The main trade-off is file size and compatibility. .FITS files are typically uncompressed and use 32-bit or 64-bit floating-point arrays, making them significantly larger than compressed .RAW files. Furthermore, standard photo editors cannot open .FITS files.

This conversion is a bad idea for standard terrestrial photography. If you want to edit a landscape photo of the night sky in standard software, convert to .TIFF or .DNG instead.

Typical Tasks and Users

This conversion is specific to astrophotography and astronomy. Common users and workflows include:

• Amateur Astrophotographers: Users shooting deep-sky objects with DSLR or mirrorless cameras who need to calibrate, align, and stack their images.
• Citizen Scientists: Amateurs providing data for exoplanet transits or variable star photometry, which requires standardized .FITS headers for time and location.
• Image Calibration: Workflows that require subtracting dark frames, dividing flat frames, and removing bias signals using linear, unprocessed sensor data.

Software & Tool Support

Astronomical software relies heavily on .FITS, while standard photography software relies on .RAW. The following tools bridge the gap:

• PixInsight: A premium, industry-standard astrophotography suite that natively converts and processes these files.
• Siril: A free, open-source astronomical image processing tool that handles conversion and stacking.
• DeepSkyStacker: A free Windows application that reads .RAW files and outputs stacked .FITS or .TIFF files.
• ASTAP: A free astrometric stacking program that converts formats and solves plate coordinates.
• Libraries: Developers use LibRaw to extract sensor data and Astropy in Python to write the .FITS arrays and headers.

Pros and Cons of the Conversion

Pros:

• Scientific Compatibility: Unlocks advanced processing techniques like plate solving, photometric color calibration, and pixel math.
• Standardized Metadata: Converts proprietary EXIF data into readable ASCII headers (e.g., EXPTIME, ISO, DATE-OBS).
• Mathematical Precision: Supports 32-bit and 64-bit floating-point data, preventing clipping during heavy image stretching.

Cons:

• File Size Bloat: Uncompressed .FITS files consume significantly more disk space than lossless compressed .RAW files.
• Loss of Editability: Standard editors like Adobe Lightroom or Capture One cannot read .FITS files.
• Bayer Matrix Complexity: If the conversion debayers the image too early, it ruins the ability to apply proper dark and flat calibration frames.

Conversion Difficulties & Why Convert.Guru

The technical pipeline for converting .RAW to .FITS is complex. The converter must extract the linear sensor data without applying gamma corrections, white balance, or noise reduction. It must also handle the Bayer matrix. For accurate astrophotography calibration, the data must remain in its monochrome, mosaiced state during conversion. Finally, the converter must parse proprietary EXIF data from dozens of camera manufacturers (Canon, Nikon, Sony) and map it accurately to standard .FITS header keywords.

Convert.Guru handles this conversion accurately. It extracts pure linear data without applying unwanted photographic adjustments. It maps critical exposure metadata to the correct headers and outputs standard-compliant .FITS files, saving users from configuring complex command-line scripts or installing heavy processing suites just to format their data.

RAW vs. FITS: What is the better choice?

Which format should you choose?

Choose .RAW for archiving your original camera files and for standard photography workflows. It is the most efficient way to store unprocessed sensor data and offers the best compatibility with commercial photo editors.

Choose .FITS when you are ready to calibrate, stack, and stretch deep-sky astrophotography data. It is mandatory for scientific measurements like astrometry (measuring positions) and photometry (measuring brightness).

Avoid this conversion entirely if your goal is to share an image online or edit a single Milky Way landscape. In those cases, process the .RAW file directly in a photo editor and export it as a .JPEG or .TIFF.

Conclusion

Converting .RAW to .FITS makes sense only when moving from consumer camera capture to advanced astrophotography processing. The biggest limitation to watch for is the massive increase in file size and the complete loss of compatibility with standard photography software. For users who need to bridge the gap between consumer hardware and scientific software, Convert.Guru provides a reliable, technically accurate conversion that preserves linear sensor data and maps critical metadata without requiring complex software installations.