https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/hdiutil.1.html
convert image -format format -o outfile convert image to type format and write the result to outfile. As with create, the correct filename extension will be added only if it isn't part of the provided name. Format is one of: UDRW - UDIF read/write image UDRO - UDIF read-only image UDCO - UDIF ADC-compressed image UDZO - UDIF zlib-compressed image UDBZ - UDIF bzip2-compressed image (OS X 10.4+ only) UFBI - UDIF entire image with MD5 checksum UDRo - UDIF read-only (obsolete format) UDCo - UDIF compressed (obsolete format) UDTO - DVD/CD-R master for export UDxx - UDIF stub image UDSP - SPARSE (grows with content) UDSB - SPARSEBUNDLE (grows with content; bundle-backed) RdWr - NDIF read/write image (deprecated) Rdxx - NDIF read-only image (Disk Copy 6.3.3 format) ROCo - NDIF compressed image (deprecated) Rken - NDIF compressed (obsolete format) DC42 - Disk Copy 4.2 image