Convert Apple iOS .DMG File to .IPSW – Apple is now always seeding their beta version of iOS as .DMG file instead of regularly .IPSW. However you’ll need the .ipsw version to restore via iTunes as well as to create custom jailbroken firmware either using Sn0wBreeze as well as PwnageTool.
So if you got -for example- iOS 5 beta 6 .DMG file and want to extract the .ipsw file inside it, so here it is nice common methods to do that.
Note: mostly people will say it as “convert .dmg to ipsw” but basically what we gonna do is to extract .ipsw from a .dmg file.
Extract .IPSW from .DMG Using TransMac
Download TransMac here [link]
Extract .IPSW from .DMG Using PowerISO
Download PowerISO here [link]
Basically TransMac and PowerISO is not a free software. Another alternative free tool to open .dmg file and extract .ipsw file contained inside it is by using 7zip tool. 7-Zip can unpack the following formats in addition to the formats it fully supports: ARJ, CAB, CHM, cpio, DEB, DMG, HFS, ISO, LZH, LZMA, MSI, NSIS, RAR, RPM, UDF, WIM, XAR and Z. Download 7zip tool here [link].