ECW (file format)

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Enhanced Compression Wavelet
File name extension	`.ecw`
Developed by	Earth Resource Mapping

ECW (Enhanced Compression Wavelet) is an open standard wavelet compression image format developed by Earth Resource Mapping. The file format is optimized for aerial and satellite imagery, and efficiently compresses very large images with fine, alternating contrast. This is a lossy compression format.

It has the following properties:

embeds map projection information
fast compression (about 1.5 MB of compressed file per second on 1 GHz processor)
typical compression ratios between 1:10 and 1:100
possible decompression of selected regions without the need to decompress the whole file
data flow compression allows for compression of big files with small RAM requirements

Despite being open standard there does not currently unfortunately seem to be any Free Software to read or write ECW^[1].

However, there are 2 programs that offer limited support:

MapWindow GIS is a Free Software GIS application that can easily read ECW files and use them in their projects,

IrfanView allows one to read and write (even bulk translated) ECW files, but it does not offer any advanced features.

[edit] Footnotes

^ Earth resource mapping offers libecw for reading ECW but it does not qualify as Free Software since the license which you can see in e.g. https://svn.zib.de/lenne3d/lib/libecw/3.3-2006-09-06/License.txt states e.g. "You are not permitted to change the ECW file format"