Krdytkyu

The following answer uses a TUI, not a GUI solution:

Depending on your use-case (I use it to make system back-ups) you can use CloneZilla Live. It can create:

• 
  sparse images,


• 
  compressed images of:
  
  
  
  
  • entire systems,
  
  
  • entire drives
  
  
  • simply individual partitions.
  
  
  
  

The main advantages are:

• that it boots from:
  
  
  
  
  • external media
  
  
  • 
    internal media
  
  
  
  


• comes with its own OS (based on Ubuntu)


• it can make exact cold system back-ups that are easily restored.

On top of all these goodies, it can copy MBRs as well.

If a cold system back-up is not what you're looking for, you can still use the technology that CloneZilla is based upon and that is partclone.

Achieving smaller disk images is usually done by ways of not copying zero outed blocks from the initial file system in the image. The concept is called sparse space in files or puching holes in files, and your host file system has to support it.
a bit command line but try this:

sudo apt-get install virt-manager qemu-utils 

And then once it's install you can use :

qemu-img convert -f raw -O raw  /dev/sdX /home/<user>/Ubuntu.img

This will create a sparse ( zeros in the file aren't written) image of your disk.
where -f = format, -O output format. sdX the disk ( can use partitions as well).
The program has advanced features such as snapshots and different output formats (vdi, vmdk, etc).
Your place where you save the image has to support sparse files, or else the size will be just as big, since zeros in the partition will be written to disk. And to make the most of it, do run a program such as sfill or zerofree found in apt on the partition, because free space does not always mean zero space, and you want to maximize the amount of zero space on the file system.

Bonus ninja points. Since linux thinks of disks as "files", then you could also use plain cp, with the condition that your output partition where you park the file knows sparse files.

sudo cp --sparse=always /dev/sdX /home/<user>/Ubuntu.img

Which will create a raw copy by means of cp..

Examples of filesystems that support sparse : ext4, btrfs, xfs, ntfs ( ntfs-3g however might not allow sparse writes).

Examples of filesystems that do not : fat32.

Edit: This will not work well if files deleted from the filesystem are still present on the partition, so first it's necessary to wipe the free space on the target partition:

1. Mount the target partition


2. Run dd if=/dev/zero of=<path_to_partition_volume>/file.dd && rm <path_to_partition_volume>/file.dd
   


3. Unmount the target partition

Then:

You can read the whole partition block by block with dd and output everything to a compression utility like gzip. Most likely any compression tool, even using the fastest/lowest compression settings, will compress all the free space during the process.

With gzip:

sudo dd if=/dev/sdX | GZIP=-1 gzip >/path/to/backup.gz

(GZIP=-1 temporarily sets the environment variable GZIP to -1 to achieve the fastest/lowest compression)

To restore a backup:

gzip -d /path/to/backup.gz >/dev/sdX

How about using ddrescue with -S option?

ddrescue -S /dev/sdXY /<path_to_backup>/backup.img

This will clone each block but zero blocks found in block device /dev/sdXY to /<path_to_backup>/backup.img

It can't be used to make a copy to a smaller drive. When I have a 64 Gb drive that is only 10% filled with data. I would like to be able to copy that to a 6 Gb imagefile, that I can copy on its turn to a 16Gb drive and than expand it to 16 gb

The only possibility I know now is use GParted to shrink the original, than copy it and then resize both. A very risky operation, since you need to shrink and resize the original.

You could use rsync to backup just the files on the partition to another partition. Or tar to create a compressed archive containing all files.

Both probably have (multiple) GUIs, but I've never used those myself.

Clonezilla can actually be quite friendly. The live CD doesn't require any command line usage - I'd be quite happy to call it a GUI even though it doesn't use the mouse - and I think the defaults are OK for a lot of cases. The problem is something you didn't explicitly call out: it doesn't seem to be designed as something you can install on an arbitrary linux system. It's packaged for Debian / Ubuntu specifically, and the Live CD is the easiest way to run it.

Clonezilla / partclone use filesystem-aware cloning and use their own compressed image format.

There's another non-GUI possibility to generate simple (mountable) sparse files, that doesn't rely on detecting zero sectors.

virt-sparsify /dev/your-block-device backup.img

If /tmp is a ramdisk it will warn that it potentially needs more space for temporary files. So you might need to add the option --tmp /var/tmp.