RIOT (Radical Image Optimization Tool)

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Radical Image Optimization Tool (RIOT for short) is a free image optimizer that will let you to visually adjust compression parameters while keeping minimum filesize.
It uses with a side by side (dual view) or single view interface to compare the original with the optimized image in real time and instantly see the resulting file size.

Main features:

• open many image types including rare/scientific types
• save and optimize JPEG, GIF and PNG with a simple, clean user interface
• works in dual view: (original – optimized image) or single view (optimized image).
  Automatic preview of resulting image
• in-place compare function (alternativelly display the original image over the optimized image to notice small pixel changes)
• compress files to desired filesize threshold
• fast processing (all is done in memory);
  see instant results including resulting filesize
• batch support (process multiple files at once)
• transparency handling options
• decide if you want to keep metadata (comments, IPTC, Adobe XMP, EXIF profiles, ICC profiles).
  Unsupported metadata is removed
• transfer metadata between image formats (destination format must support them)
• common tools: pan and zoom, rotate, flip
• basic image adjustments: brightness, contrast, gamma, invert
• visually reduce number of unique colors for PNG and GIF images in order to reduce filesize
  (two quantization methods are available: Xiaolin Wu and NeuQuant neural net)
• resize image by using well known resample filters (ex: Lanczos3, Catmull Rom, Bicubic, and others)
• out-of-the-box support for external PNG optimizers (optipng, pngout, etc)
• the compression and the results are comparable to those of commercial products, even higher.
• Adaptive logarithmic tone mapping algorithm (Drago) used for HDR images