File extension

.img

ERDAS IMAGINE (IMG) raster format

.img files in this context are ERDAS IMAGINE raster images: a geospatial raster format (HFA) used in remote sensing and GIS to store multi-band imagery together with georeferencing, statistics, and pyramids.

Known meanings

Formats and reference material for .img

ERDAS IMAGINE (IMG) raster format

Hierarchical (HFA) geospatial raster format for multi-band imagery and GIS data

  • gis-formats
  • ERDAS / Hexagon Geospatial
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Details

Format notes

ERDAS IMAGINE (IMG)

The .img extension here refers to the ERDAS IMAGINE raster format, a widely used container for geospatial imagery in remote sensing and GIS. It stores gridded raster data — satellite and aerial imagery, elevation models, classification results, and other continuous or categorical rasters — along with the metadata needed to place that data on the Earth’s surface.

The underlying structure is the Hierarchical File Architecture (HFA), a tree of typed nodes. This lets an .img hold multiple bands, per-band statistics and histograms, a color table, a map projection and georeferencing, and reduced resolution overviews (“pyramids”) for fast display, all inside one file. Large datasets may accompany the .img with auxiliary files, so the raster is not always a single standalone file.

Note: .img is a heavily overloaded extension. It is also used for raw disk and CD/DVD images, floppy images, and other unrelated formats. An .img file should be identified by its content and context, not by extension alone.

Capabilities And Tooling

Because it was designed for analytical imagery, the format supports many data types (from single-bit and 8-bit through floating point), large files, and rich attached metadata. It is broadly supported by GIS and remote-sensing software, and open tools such as GDAL implement the HFA driver for reading and writing .img, which makes it a practical interchange format across ecosystems.

Preservation Notes

For preservation and transfer, keep any sidecar files together with the .img, and record the coordinate reference system, pixel size, band definitions, and nodata value, since analytical value depends on correct georeferencing and band semantics. When converting to another raster format such as GeoTIFF, preserve the projection, nodata handling, and statistics rather than only the pixel values.

Security Notes

As a structured binary format with nested nodes and variable-length records, an .img parser should validate node offsets, band and dimension counts, and allocation sizes from untrusted files before trusting them, to avoid out-of-bounds reads or excessive memory allocation.

Further Reading

  • GDAL HFA (.img) driver: https://gdal.org/drivers/raster/hfa.html
  • ERDAS IMAGINE product overview: https://en.wikipedia.org/wiki/ERDAS_IMAGINE