Here's how you can install the Nomacs image viewer in Ubuntu 14.04. Nomacs Image Lounge can handle most image formats including RAW images.
1. Open a terminal window.
2. Type in the following commands then hit Enter after each.
sudo add-apt-repository ppa:nomacs/stable
sudo apt-get update
sudo apt-get install nomacs
It also includes other main editing features such as: crop, color correction, brightness and contrast, resize, saturation, hue, gamma, exposure, and create mosaic images from multiple pictures, etc. Additionally it allows user to compare images and spot the differences between both. Drag 'n' Drop operation is supported or you may can add images from directory or add single image and multiple images can be browsed easily.More at Noobs Lab
Additional resources for Nomacs Image Lounge