Learn about sparse image (extension .sparseimage) files. The sparse image file type is primarily associated with OS X. It is a disk image format similar to DMG. Sparse image files take up less disk space, only using space for data stored in them. They can be created using Apple Disk Utility.
Earlier versions of OS X FileVault feature used encrypted sparse images to secure user home directories. Newer FileVault uses .sparsebundle format instead. Files with .sparseimage extension can be opened using Apple Disk Utility. It may be possible to expand the image back to ISO or DMG formats.
To create a sparse image in Disk Utility, click “New Image” and choose “sparse disk image” from the menu. Over 400 file formats can be opened with File Viewer Plus software. The Windows Registry can also associate .sparseimage extension to corresponding software. Many files contain only simple text data. Files using .sparseimage extension grow as user adds data, using less disk space.
Disk Utility
hdiutil Command-Line Tool