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New Installer: Tarball Images
The installation of many RPMs can take quite a lot of time. For speeding this up, openSUSE introduced set of images.
Based on software selection, the installer evaluates the best image set (which matches the software selection best), deploys this set of images, and installs or removes packages to match packages which user selected.
The image sets are predefined by the media; YaST is not able to freely combine the images and install any subset of them. The reason is that each set also has to define the RPM database after its images are deployed; there is no way to reconstruct the RPM database and after image set is deployed, the RPM database must match the installed packages (resp. packages included in the image set).
The reason to have image sets is to reduce the space requirement on the media. If there were e.g. KDE and GNOME system images on the media, a lot of stuff (basic utilities, X11) would be included in both of the images. Currently, the KDE and GNOME image sets share one or more base system images and each of them provides one or more additional images to complete the package set.
In openSUSE, the images are implemented as compressed tarballs. This format is the most convenient, as unlike disk images, one can untar multiple archives to the same filesystem or to multiple filesystems; layout of such filesystems does not need to match how files are spread across multiple tarballs.
The best matching image set is evaluated based on selected patterns. This is, of course, most effective if users only select patterns and do not fiddle too much with individual package selection.
After images are deployed, the installer reinitializes the target (in order to read the RPM database deployed with the image) and finishes the installation, which means to remove the superfluous packages and install the missing ones.
Image installation can only be used for new system installation; it does not help to speed up upgrade or on-line migration.