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Default raster formats supported by DWG files do not include the ECW format before AutoCAD 2012
AutoCAD 2012 support additional raster file formats (.psd, .dds, .doq, .ecw, .hdr, .jp2, .j2k, .sid, .nitf, .exr)
If you are aware of this limitation, but still want your raster to export to DWG, edit the following configuration variable in the workmode.cfg file:
_USTN_CAPABILITY_DWG < +CAPABILITY_RASTER_ALL_TYPES
This will allow opening of all supported raster types.
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