My understanding of a image backup is that it backs up everthing on you hard drive. My hard drive has 84GB of used space. Here is what I don't understand and maybe someone could clear up for me. When I do an image backup in windows 7 it shows on backup drive that I used 45Gb of space for the image backup. Is windows 7 condensing the data with the backup? Or is something else going on here or is there something wrong.
Thanks for any help.

Yes windows 7 creates a image which takes up far less GB than say a clone of the drive,

Thanks all the replies.