nomacs is a free and open source image viewer, editor.
nomacs, based on OpenCV, QT – can read RAW and psd files along with all common image formats. It also have features to display thumbnails, histogram, meta data etc of an image. GUI of nomacs comes with folder browsing option along with image thumbnail list. It can also browse image directly from zip files.

nomacs image editing features contains options to change brightness, contrast, saturation, hue, gamma and exposure. You can also create false color images using pseudo color function. “A unique feature of nomacs is the synchronization of multiple instances. With this feature you can easily compare images by zooming and/or panning at the exactly same position or even by overlaying them with different opacities.”
nomacs recently launched version 3.4 with introduction of its batch processing UI. You can save common batch configurations in a file for later use. You can refer to the release notes for more details.
How to Install
nomacs team provides nomacs installer for most of popular Linux distributions including a Windows installer as well.
To install nomacs in Ubuntu 16.04 Xenial Xerus, add below PPA and install.
sudo add-apt-repository ppa:nomacs/stable sudo apt-get update sudo apt-get install nomacs
For other installers, visit download page.
You can follow nomacs developments and report bugs @ GitHub