Convert FITS to SGI

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FITS vs SGI Format Comparison

Aspect FITS (Source Format) SGI (Target Format)
Format Overview
FITS
Flexible Image Transport System

Scientific image format developed by NASA and the International Astronomical Union FITS Working Group (IAUFWG), first defined in 1981. Supports 8/16/32/64-bit integer and 32/64-bit floating-point pixel data with multi-extension architecture for storing multiple images and tables per file. Includes WCS (World Coordinate System) metadata for celestial coordinate mapping. The standard data format for astronomical observatories worldwide.

Lossless Standard
SGI
Silicon Graphics Image

Raster image format developed by Silicon Graphics Inc. for IRIX workstations. Supports 8-bit and 16-bit per channel with optional RLE compression. Historically important in professional 3D graphics, scientific visualization, and film production.

Standard Format Lossless
Technical Specifications
Data Types: 8/16/32/64-bit integer, 32/64-bit float
Structure: Multi-extension (images, tables, headers)
Metadata: WCS celestial coordinates, extensive headers
Byte Order: Big-endian (FITS standard)
Extensions: .fits, .fit, .fts
Color Depth: 8-bit or 16-bit per channel
Compression: None or RLE
Channels: 1 (grayscale) to 4 (RGBA)
Byte Order: Big-endian
Extensions: .sgi, .rgb, .bw
Image Features
  • Data Types: Integer (8-64 bit) and floating-point (32-64 bit)
  • Multi-Extension: Multiple images and binary tables per file
  • WCS Metadata: World Coordinate System for celestial mapping
  • Header Keywords: Extensive ASCII keyword-value metadata
  • Dynamic Range: Full floating-point for scientific flux data
  • Coordinate Systems: Equatorial, galactic, ecliptic reference frames
  • 8-bit and 16-bit per channel depth
  • RLE compression option
  • 1-4 channel support (grayscale to RGBA)
  • Big-endian byte order
  • Simple flat file structure
  • Historical SGI workstation standard
Processing & Tools

FITS data handling with astropy and Python:

from astropy.io import fits
import numpy as np

# Open FITS file with full header access
hdul = fits.open('observation.fits')
header = hdul[0].header  # WCS, telescope info
data = hdul[0].data       # Pixel array

# Access multi-extension data
for ext in hdul:
    print(ext.name, ext.data.shape if ext.data is not None else 'No data')
SGI image from FITS astronomical data:
from astropy.io import fits
from PIL import Image
import numpy as np

hdul = fits.open('supernova.fits')
data = np.clip(hdul[0].data, 0, 255).astype('uint8')
img = Image.fromarray(data).convert('RGB')
img.save('supernova.sgi')
Advantages
  • Full floating-point dynamic range for scientific data
  • Multi-extension architecture for complex datasets
  • WCS metadata preserves celestial coordinate information
  • Extensive header keywords for observation metadata
  • Universal standard across all astronomical observatories
  • Supported by every major astronomical software package
  • 16-bit per channel depth
  • Lossless RLE compression
  • Simple and fast to process
  • Historical scientific computing format
  • Pillow native read/write
  • Multi-channel support
Disadvantages
  • Not viewable in standard image viewers or browsers
  • Requires specialized astronomical software
  • Large file sizes for high-resolution observations
  • Big-endian byte order can cause processing overhead
  • Complex multi-extension structure
  • Niche format with limited modern use
  • Big-endian byte order can cause issues
  • No animation or transparency standards
  • Largely obsolete outside legacy workflows
  • Limited modern tool support
Common Uses
  • Space telescope observations (Hubble, JWST, Chandra)
  • Ground observatory data (VLT, Keck, Gemini)
  • Sky survey archives (SDSS, 2MASS, Gaia)
  • Solar observation data (SDO, SOHO)
  • Radio astronomy imaging (ALMA, VLA)
  • Legacy SGI IRIX workstation compatibility
  • Scientific visualization archives
  • Film production legacy workflows
  • 3D graphics texture storage
  • Historical data preservation
Best For
  • Scientific astronomical observations with precise flux data
  • Multi-band imaging campaigns requiring coordinated datasets
  • Archival storage with full observation metadata
  • Pipeline processing requiring WCS coordinate transforms
  • Legacy SGI workstation astronomy software compatibility
  • Scientific visualization archives from observatories
  • 16-bit depth preservation for astronomical data
  • Historical astronomical data format migration
Version History
Introduced: 1981 (NASA/IAU FITS Working Group)
Current: FITS Standard 4.0 (2018)
Status: Active, universal astronomical standard
Evolution: FITS 1.0 (1981) → 2.0 (1988) → 3.0 (2008) → 4.0 (2018)
Introduced: 1984 (Silicon Graphics Inc.)
Format: SGI RGB / IRIS
Status: Legacy, declining use
Evolution: SGI IRIX native (1984) → cross-platform support → legacy
Software Support
Astronomy: ds9, IRAF, PixInsight, Aladin, TOPCAT
Libraries: astropy (Python), cfitsio (C), FITSIO (IDL)
Space Agencies: NASA HEASARC, ESA archives, MAST
Other: ImageMagick, GIMP (via plugin), Pillow (limited)
Original: SGI IRIX workstations
Libraries: Pillow, ImageMagick, OpenCV
Viewers: IrfanView, XnView, display (IRIX)
Other: GIMP, ffmpeg

Why Convert FITS to SGI?

Converting FITS to SGI format addresses compatibility with legacy Silicon Graphics workstations and their software ecosystem. Many astronomical institutions operated SGI IRIX systems for decades, and some legacy software and archives still use the SGI image format.

SGI format's 16-bit per channel support makes it one of the few legacy formats capable of preserving higher bit-depth from FITS data. This is relevant when migrating astronomical data to or from systems that use the SGI image format as their native raster format.

Historical VFX production pipelines that processed astronomical imagery for planetariums and science documentaries often used SGI format. Converting FITS to SGI maintains compatibility with these established workflows and archived project files.

The conversion reads FITS data and produces SGI files with optional RLE compression. The big-endian byte order of both FITS and SGI formats aligns naturally, and the simple flat-file structure ensures reliable data transfer.

Key Benefits of Converting FITS to SGI:

  • 16-Bit Depth: Preserves FITS 16-bit data, unlike most legacy formats limited to 8-bit
  • Legacy Compatibility: Essential for SGI IRIX workstations still operating in some institutions
  • RLE Compression: Optional compression reduces file sizes for storage-constrained systems
  • Historical Archives: Access and maintain compatibility with historical astronomical data collections
  • VFX Pipeline: Compatible with legacy film production and planetarium rendering workflows
  • Simple Structure: Flat file format with straightforward read/write implementation
  • Big-Endian Native: Natural byte-order alignment with FITS format eliminates swap overhead

Practical Examples

Example 1: Legacy SGI Workstation Compatibility

Scenario: A research institution maintains SGI IRIX workstations for legacy astronomical software and needs to convert modern FITS data for display on these systems.

Input FITS file (hst_archive.fits):

FITS astronomical data:
  Resolution: 2048×2048 HST image
  Data: WFPC2 archival data
  Instrument: Hubble WFPC2
  Content: Deep field observation

Output SGI file (hst_archive.sgi):

Converted SGI output:
  SGI IRIX native format
  16-bit depth preserved
  RLE compressed output
  Legacy workstation display

Example 2: VFX Film Production Pipeline

Scenario: A visual effects studio using SGI-format texture pipelines (from legacy film production tools) converts astronomical imagery for use in a space documentary.

Input FITS file (nebula_plate.fits):

FITS astronomical data:
  Resolution: 4096×4096 nebula composite
  Data: Ha/OIII/SII palette
  Instrument: Large-format telescope
  Content: Veil Nebula supernova remnant

Output SGI file (nebula_plate.sgi):

Converted SGI output:
  VFX pipeline compatible
  Film production standard
  Multi-channel RGB
  High-quality texture input

Example 3: Scientific Visualization Archive

Scenario: A computational astrophysics lab archives simulation visualization output in SGI format for compatibility with their long-running data visualization infrastructure.

Input FITS file (simulation_output.fits):

FITS astronomical data:
  Resolution: 1024×1024 simulation frame
  Data: N-body simulation render
  Instrument: Supercomputer output
  Content: Galaxy collision simulation

Output SGI file (simulation_output.sgi):

Converted SGI output:
  Visualization archive format
  Historical consistency
  Simple file structure
  Infrastructure compatible

Frequently Asked Questions (FAQ)

Q: What is FITS format?

A: FITS (Flexible Image Transport System) is the universal astronomical data format since 1981, developed by NASA and the IAU. It stores scientific observations with floating-point precision and celestial coordinate metadata.

Q: What is SGI format?

A: SGI (Silicon Graphics Image) is a raster format from Silicon Graphics workstations, supporting 8-bit and 16-bit per channel with optional RLE compression. It was historically important in scientific visualization and film production.

Q: Why convert FITS to SGI?

A: Converting FITS to SGI is relevant for legacy SGI workstation compatibility, historical VFX production pipelines, and scientific visualization archives. It's particularly useful when working with older astronomical software that runs on IRIX systems.

Q: Does SGI support 16-bit per channel?

A: Yes, SGI format supports both 8-bit and 16-bit per channel, making it one of the few legacy formats that can preserve higher bit-depth from FITS data. This is useful for maintaining astronomical data precision.

Q: Is SGI format still used?

A: SGI format has largely been superseded by PNG, TIFF, and EXR. It remains relevant only for legacy system compatibility, historical archive access, and specific VFX production tools that still support it.

Q: What is the byte order of SGI files?

A: SGI files use big-endian byte order, matching FITS format's big-endian convention. This means no byte-swapping is needed when converting between the two formats on big-endian systems.

Q: Can SGI store alpha transparency?

A: Yes, SGI format supports up to 4 channels (RGBA), providing full alpha transparency. However, not all SGI-compatible software correctly handles the alpha channel.

Q: What modern tools can read SGI files?

A: Pillow, ImageMagick, GIMP, IrfanView, XnView, and FFmpeg can all read SGI files. Most modern image editors provide at least read support for this format.