When comparing Phototonic vs Gwenview, the Slant community recommends Gwenview for most people. In the question“What are the best FOSS image viewers for UNIX-like systems?” Gwenview is ranked 11th while Phototonic is ranked 15th.
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 Easy to navigate folders
Pro Quickly view image metadata
Pro Easily resize, crop, flip and rotate
Pro Keyboard shortcuts can be redefined
Pro Images can be sorted by name, date and size
Cons
Con No Dark mode
And not a lot of customization available.
Con No WebP image format support
Con Has a bug that causes certain png files to show brighter than normal
The image, if is a png that contains gamma information, will appear washed out. There is still an open ticket concerning this issue.
Con Very slow on remote folders
Compared to others, like XNview, is VERY slow when retrieving images from shared folders (NFS or Samba).
Con Not lightweight
Needs a lot of KDE packages.