Under Drive imaging/Imaging options/Image file you find the settings Compress image file to save storage space. You can choose from the LZNT1 Standard or theBZIP2 process.
LZNT1:This is a compression type based on the Lempel-Ziv algorithm, which is laid out on a real time application. Speed is preferred over the rate of data compression.
BZIP2: is a block type compression process. Compression rate is preferred over velocity.
You can also compress the image after creation under Convert image file in the Tools menu.
Note: Compression increases the time required to create an image file. However, the file then requires less space on the disk.