LinuxWhat is the ECW file format?
.ecw is a proprietary wavelet compression format optimized for aerial and satellite imagery, developed by Earth Resource Mapping and now owned by Hexagon (via ERDAS and Intergraph). .ecw files hold data gathered with satellite or aerial cameras, always accompanied by embedded geospatial coordinate metadata.
The format is designed to meet the needs of geolocation and data mapping. Images in this format are used alongside geospatial data in GIS platforms such as QGIS and ArcGIS.
Image data stored in an .ecw file are compressed using a lossy wavelet algorithm with minimal perceptible quality loss. This type of file is ideal for large-format imagery because the ECW compression algorithm handles very large rasters efficiently, reaching compression ratios from 1:10 to 1:100 - a range hard to achieve with conventional formats such as GeoTIFF. ECW supports up to 8 bits per band and up to 255 image bands, accommodating multi-spectral as well as standard RGB imagery; ECW version 3 extended per-band depth to 16 bits.
Files are identified by the ASCII signature eW (hex 65 57) at byte offset 0. The ERDAS ECW/JP2 SDK writes both .ecw and JPEG 2000 files - the two formats carry distinct signatures and are not interchangeable. Large datasets can be streamed tile-by-tile using the ecwp:// protocol.
Security & safety
RISK: LOWECW is passive raster imagery with no scripting, so the file itself is low-risk. The practical cautions are licensing and provenance: ECW decoding is free but the codec is proprietary (Hexagon), so some open-source builds omit the ECW driver; and aerial/ satellite imagery can be sensitive or licence-restricted data - respect the provider's terms. Avoid sketchy 'ECW viewer' download sites that bundle adware; use IrfanView, XnView, QGIS or GDAL from their official pages.
Format details
in a nutshellPrograms that open ECW files
Windows7 apps
IrfanView
Free Install IrfanView plus its plugin pack (the ECW plugin uses the Hexagon decoder), then File > Open the .ecw to view/export. 
QGIS
Open-source Layer > Add Raster Layer > select the .ecw - opens with full georeferencing via the bundled GDAL ECW driver. Best free GIS option. 
GDAL (gdal_translate)
Open-source Command line: gdal_translate in.ecw out.tif - reads ECW (free decode) and converts to GeoTIFF/JPEG/PNG/etc.
ArcGIS Pro / ArcGIS Desktop
Paid Add the .ecw as a raster layer; reads ECW natively. (db lists legacy ArcGIS Desktop - ArcGIS Pro is the current product.)
FME Form (FME Desktop)
Paid Read ECW and transform/convert it within data pipelines. (Rebranded 'FME Form'; db 'FME Desktop' is the old name.) 
macOS2 apps
QGIS
Open-source Add Raster Layer to open the .ecw via GDAL on macOS - the main free option (most Mac image apps can't read ECW). 
Technical details
deep spec| File signature (magic bytes) | `65 57 01 06` at byte offset 0 - ASCII `eW` followed by `0x01 0x06` |
| MIME type | `image/x-ecw` |
| Compression method | Lossy discrete wavelet transform (DWT) with hierarchical subband decomposition |
| Typical compression ratio | 1:10 to 1:100 with minimal perceptible quality loss |
| Bit depth per band | 1 to 8 bits per band per channel in the standard format |
| Maximum image bands | Up to 255 bands, enabling multi-spectral and hyperspectral imagery |
| Embedded georeferencing | CRS, datum, and geographic bounding box stored directly in the file header |
| Streaming protocol | `ecwp://` (ECW Streaming Protocol) for progressive, tile-based network delivery |
| Internal color transform | RGB imagery converted to YCbCr internally before wavelet encoding; greyscale encoded directly |
| Progressive decoding | Hierarchical wavelet tree allows decoding at multiple resolutions without reading the full file |
| Typical file-size reduction | A 1 GB aerial mosaic commonly compresses to under 50 MB with acceptable visual quality |
| Encoding SDK | Write access requires the proprietary ERDAS ECW/JP2 SDK (Hexagon Geospatial); GDAL provides read access in licensed builds |
| Command-line conversion | Convert to GeoTIFF via `gdal_translate -of GTiff input.ecw output.tif` |
| Primary application domain | Aerial ortho-photography, satellite basemaps, and large-scale topographic mapping |
| Released | 1998 (Earth Resource Mapping, Perth, Australia - alongside Image Web Server) |
| Specification | gdal.org |
ECW conversions
Community Q&A
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