When comparing Ristretto vs Phototonic, the Slant community recommends Phototonic for most people. In the question“What are the best FOSS image viewers for UNIX-like systems?” Phototonic is ranked 15th while Ristretto is ranked 19th. The most important reason people chose Phototonic is:
Beside being pretty clean and easy-to-use, the UI is also pretty fast.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Fast startup
Pro Lightweight
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.
Cons
Con Lack of critical shortcuts and functions like moving the image up and down once zoomed (something like Alt+Down/PgDown on some viewers)
Con Crashes sometimes on large images
Con No Dark mode
And not a lot of customization available.