Faststone Image Viewer

FastStone Image Viewer is a free image browser, editor, and converter for Windows. It opens common formats (JPEG, PNG, BMP, GIF, TIFF, WebP) along with RAW files from Canon, Nikon, Sony, and other camera manufacturers. The program combines a file browser with a fullscreen viewer, basic editing tools, and batch processing. A portable version runs from a USB drive without installation.

What it does

The main window shows a folder tree on the left and thumbnail previews on the right. Double-click any image or press Enter to switch to fullscreen mode, where you navigate with arrow keys. In fullscreen, moving the mouse to the left edge reveals an editing panel with crop, resize, color adjustment, red-eye removal, and drawing tools. All edits apply to the current image and you save with a single keystroke.

Batch Convert (F3) processes hundreds of files at once. Select images, pick an output format, and optionally apply transformations through Advanced Options: resize, rotate, add watermark, adjust brightness, change DPI, add text overlay. Batch Rename (F4) renames files using templates with sequential numbering, date stamps, or original filename components. These two features alone replace dedicated batch processing software for most photographers.

The comparison tool displays up to four images side by side with synchronized zoom and pan, useful for picking the best shot from a series. Screen capture grabs the full screen, a window, a rectangle, or a freeform shape, with a built-in annotation editor for arrows and text.

Who it is for

I use FastStone as my default image viewer because it opens everything fast, displays RAW files without extra software, and handles batch jobs that would take forever one by one. If you need a lightweight viewer that also crops, resizes, and converts without loading a full editor, this is the best free option on Windows.