To convert a MrSID (Multiresolution Seamless Image Database) from LizardTech you’ll need GDAL (Geospatial Data Abstraction Library) — Mac Users: download here — along with its MrSID Plugin — Mac Users: scroll down at link above.
Once both are installed you can use
gdal_translate to do the actual conversion. Beware that converting will give you a gigantic file and will take a while. Best is to resize the output, to not end up with images of 500MB.
Convert MrSID to PNG and resize
/Library/Frameworks/GDAL.framework/Programs/gdal_translate -of PNG -outsize 10% 10% input.sid output.png
More info on the parameters can be found on the GDAL site.
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