Ristretto

Eye of GNOME is an image viewer. With it you can view images of almost any type. You can manage large collections of images and can display a slideshow. You can also make basic changes to photos like rotating or flipping them, or converting them to a different file format. The images should automatically open in the Image Viewer when you double-click an image file in the file browser. If this is not the case, you should make Image Viewer the default application for viewing images. You can zoom in and out to show more or less of an image on the screen. It is useful if you want to see a large image completely or if you want to inspect the details of an image. The Image Viewer tries to guess the file format to save the image in based on the file extension you choose. If you don't recognize the file extension you type, or if you don't know which one to use, click Supported Image Files in the Save Image window. This will allow you to choose a file type from the drop down box.

Pixea is an image viewer for macOS with a nice minimal modern user interface. Pixea works great with JPEG, HEIC, PSD, RAW, WEBP, PNG, GIF, and many other formats. Provides basic image processing, including flip and rotate, showing a color histogram, EXIF, and other information. Supports keyboard shortcuts and trackpad gestures. Shows images inside archives, without extracting them. Supports JPEG, HEIC, GIF, PNG, TIFF, Photoshop (PSD), BMP, fax images, macOS and Windows icons, radiance images, and Google's WebP. RAW formats Leica DNG and RAW, Sony ARW, Olympus ORF, Minolta MRW, Nikon NEF, Fuji RAF, Canon CR2 and CRW, Hasselblad 3FR. Sketch files (preview only) and ZIP archives. Export JPEG, JPEG-2000, PNG, TIFF, and BMP. Pixea supports animated GIF, PNG, and WebP images.