Install Darktable 1.6.4 in Ubuntu 14.10/Linux Mint 17

A new release of Darktable, an open source photo workflow software, was announced a few days ago with various improvements, new camera support and translation updates.
Darktable 1.6.4 changelog, according to the release note:
General improvements:

• major rawspeed update
• facebook exporter update (first authentication usability should be much better now)
• first run opencl benchmark to prevent opencl auto-activation if GPU is obviously slower than CPU
• lensfun cornercase fixes
• some mask cornercase fixes
• zonesystem now updates it’s gui when number of zones changes
• spots iop updates
• ui_last/gui_language should work more reliably now
• internal lua updated from 5.2.3 to 5.2.4 (distro typically use their own version of lua)
• gcc 5 should build now

Camera support:

• Canon Digital Rebel (non-european 300D)
• Nikon D5500 (experimental)
• Olympus E-M5 Mark II (experimental)
• Samsung NX500 (experimental)

White balance presets:

• Sony A77 II
• Fujifilm X-E2
• Olympus E-M5 Mark II

Noise profiles:

• Canon 7D Mark II

updated translations:German, French, Russian, Danish, Catalan, Japanese, Dutch.
How to Install/Upgrade Darktable in Ubuntu/Linux Mint:
For Ubuntu 14.04, Ubuntu 14.10, and Linux Mint 17, the new release is available for upgrade in PPA repository.
1. Open terminal from the Dash, Menu, or by pressing Ctrl+Alt+T on keyboard. When it opens, run command to add PPA:

sudo add-apt-repository ppa:pmjdebruijn/darktable-release

2. After adding the PPA, you should be able to upgrade the software through Software Updater (or Update Manager):

Or you can run below commands one by one to install it from terminal:

sudo apt-get update  sudo apt-get install darktable

That’s it. Enjoy!