I'm looking for a Linux file manager with a resizable preview pane that fits full images rather than showing low-resolution cached thumbnails. I'd also like to pin folders in the sidebar and have previews load quickly.
JPG and PNG are the main formats I need. Animated GIF or WebP support would be a bonus, as would zooming with the mouse wheel over the preview.
Try Dolphin. Its resizable information panel can show an image fitted to the available space without relying on a saved thumbnail, and you can pin folders to the sidebar.
GIF previews are supported, and videos can be played in the panel too. Images are scaled down to fit but not enlarged beyond their original size. Preview speed and mouse-wheel zoom are worth testing for your files, since those details aren't established here.
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w.604+spoolmark:
Video previews can be set to play automatically. Otherwise, you need to click play.