Imagine (.img) Reader

Intergraph Corporation has contracted with me to write an Erdas Imagine (.img) to GeoTIFF raster translator. They have gratiously agreed to release the source to the translator under an OpenSource license.

Please note that I am not an employee of Intergraph, and represent them in no way.

The reader consists of a C++ API for reading any information from the Erdas Imagine heirarchical file architecture files, and a high level program for translating raster and georeferencing data to GeoTIFF. At this time the API is not really adequately documented ... if you have an interest in using the API please contact me and I will bundle it up more cleanly.

The API also supports writing a minimal Imagine file. In addition to it's utilization in img2tif, the API is also incorporated into GDAL which provides translation tools to and from Imagine format.

img2tif

The img2tif program converts an Imagine .img file into one or more GeoTIFF files.

Usage: img2tif [-i img_filename] [-o tif_basename] [-c] [-v n...]
       [-rgb [red_band green_band blue_band]] [-?] [-quiet]

Arguments:
    -i    input .img file
    -o    output base file name
          Output files will be named base_name1.tif ... base_nameN.tif,
          where N = no. of bands.
    -rgb  produce an RGB image file from the indicated band numbers
          within an existing imagine file.
    -s    output file is in strips (tiles is default)
    -c    packbits compress flag (def=uncompressed)
    -v    overview sampling increment(s) (0=single, 98=full set minus 2x,
          99=full set)  Examples: -v 2 4 8   -v 0   -v 99
    -quiet Don't produce a translation report.
    -?    Print this explanation of command line arguments

Download:

img2tif_src.zip: img2tif source code as a zip file (circa March/2006).

Things to note:

By default the program creates one GeoTIFF file for each band in the Imagine file. An RGB TIFF file can be created by specifing three bands to use as red, green and blue.
eg. img2tif -rgb 1 2 3 -i irvine2.img -o irvine123.tif
The -s flag can now be used to generate strip oriented TIFF files instead of tiled files. Many applications don't support tiled TIFF files, including older versions of ArcView.
The -v flag can be used to generate overview pyramids. For instance -v 2 4 8 would generate 1/2, 1/4 and 1/8 resolution overviews. By default none are generated, but any existing on the Imagine file are copied over.
If no output file specification is provided, the program will report selected information about the input file.
eg. img2tif -i irvine2.img
The undocumented -dt flag can be used to dump a tree of the datastructures in the Imagine file. The undocumented -dd flag can be used to dump the Imagine data dictionary. This text dump is an example of both together.

Other Imagine Format Resources

Imagine File Format Documents in PostScript: Overview and Detailed
Imagine File Format Documents in PDF: Overview and Detailed
Erdas .img Access Utility - Contains format docs, and libraries (I used the docs, but not the libs).
Text Dump of the .img file structure for a sample file. The data dictionary parser, and tree walkers are working quite well now.
Erdas Imagine .ige file format ... used for images larger than 4GB.

Credits

The img2tif translator was written by Frank Warmerdam (warmerdam@pobox.com). Suggestions for improvement are welcome.

The development of this utility was funded by Intergraph Corporation who agreed for it to released freely.

The development of Erdas Imagine write support was funded by PCI Geomatics, for whom I am incorporating it into GeoGateway.

The img2tif utility uses the libtiff library written by Sam Leffler, and the libgeotiff library written by Niles Ritter.

Thanks to Dave Mayes of BAE Systems, for providing sample files demonstrating the compressed format.