When comparing kphotoalbum 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 kphotoalbum is ranked 17th. The most important reason people chose Phototonic is:
Beside being pretty clean and easy-to-use, the UI is also pretty fast.
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Pros
Pro You can annotate images and search them using these annotations
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 Not lightweight, needs a lot of KDE packages
Con No Dark mode
And not a lot of customization available.