Convert a disk image to another format using Disk Utility on Mac
You can convert the image format and encryption of a disk image.
For example, if you create a read/write disk image but later want to prevent changes to the image, you can convert it to one of the read-only disk image formats.
In the Disk Utility app
on your Mac, choose Images > Convert, select the disk image file you want to convert, then click Open.Click the Image Format pop-up menu, then choose a new image format.
Read-only: The disk image can’t be written to, and is quicker to create and open.
Compressed: Compresses data, so the disk image is smaller than the original data. The disk image is read-only.
Read/write: Allows you to add files to the disk image after it’s created.
DVD/CD master: Can be used with third-party apps. It includes a copy of all sectors of the disk image, whether they’re used or not. When you use a master disk image to create other DVDs or CDs, all data is copied exactly.
Hybrid image (HFS /ISO/UDF): This disk image is a combination of disk image formats and can be used with different file system standards, such as HFS, ISO and UDF.
If you want to change the encryption, click the Encryption pop-up menu, then choose an encryption type.
Enter a new name for the image in the Save As field, click Save, then click Done.