XnView
XnView MP/Classic is a free Image Viewer to easily open and edit your photo file. The Image Viewer supports all major image formats (JPEG, TIFF, PNG, GIF, WEBP, PSD, JPEG2000, OpenEXR, camera RAW, HEIC, PDF, DNG, CR2). As Image Viewer you have features like color adjusting, image resizer, cropping, screen capture, metadata editing (IPTC, XMP) and much more. With its easy-to-use explorer-like interface, XnView MP allow you to quickly view your images and photos, but also to make image management. You have features like batch rename, batch converter, duplicate image finder, image compare, but you can also create contact sheets, slideshow.
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Fotoxx
Fotoxx is a free open source Linux program for image editing and collection management. The goal is to meet the needs of serious photographers while remaining fast and easy to use. Navigate a large image collection using a thumbnail browser, click on an image to view or edit. A rich set of edit and retouch functions is available. Import RAW files and edit with deep color. Save revised images as JPEG, PNG (8/16 bits/color), or TIFF (8/16). Select an object or area within an image (freehand draw, follow edges, flood matching tones), apply edit functions, copy and paste, resize, blend, warp, etc. without using layers. Edit functions have fast feedback using the full image. Edit image metadata (tags, geotags, dates, ratings, captions). Search images using any combination of metadata and file and folder names or partial names. Click a marker on a scalable world map to view all photos from that location.
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Image Viewer Ultimate
Image Viewer Ultimate is a great application to view/run slideshows of your images/photos and it is also having batch resize and batch watermark features. Fit to actual size, zoom in, zoom out, full-screen mode, and play images as a slide show on Windows. Set slideshow time, setting available through application preferences. Supports retina display. Can export images as JPEG, PNG, TIFF, JIF, BMP. Batch conversion to the desired format as JPEG, PNG, TIFF, JIF, or BMP. Batch watermark to desired images. Save images in the desired size.
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Pixea
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.
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