When comparing Phototonic vs GPicView, the Slant community recommends GPicView for most people. In the question“What are the best FOSS image viewers for UNIX-like systems?” GPicView is ranked 13th while Phototonic is ranked 15th. The most important reason people chose GPicView is:
When opening multiple images at once it opens every single picture in a separate window.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Clean and functional UI
Beside being pretty clean and easy-to-use, the UI is also pretty fast.
Pro Can be easily keyboard driven
Lots of pre-defined keyboard shortcuts.
Pro Highly customizable
Lots of options to personalize your experience. You can set Photonic to fit images by width and height, or width or height; rotate according to Exif orientation; show/hide image name in viewer; adjust space between thumbnails; adjust delay between slides.
Pro Multiple windows
When opening multiple images at once it opens every single picture in a separate window.
Pro Functional
It has all the necessary functions that you can reasonably expect from a lightweight image viewer: you can view all the image files in a directory, rotate and save them.
Pro Customizable
Pro Extremely lightweight
And still you can browse all images in a directory.
Cons
Con No Dark mode
And not a lot of customization available.