Radical Image Optimization Tool (RIOT) is a free image optimizer which will let you to visually adjust compression parameters while keeping minimum filesize!
This photo optimizer has an easy to use interface to compare the original with the optimized image in real time and instantly see the resulting file size. RIOT is lightweight, fast and simple to use, and powerful for advanced users.

Features of RIOT:

1). Open many image types including rare/scientific types

2). Save and optimize JPEG, GIF and PNG with a simple, clean user interface

3). Automatic optimization selects the most suitable format and parameters

4). Works in dual view: (original – optimized image) or single view (optimized image).

5). Automatic preview of resulting image

6). Resize image by using well known resample filters (ex: Lanczos3, Catmull Rom, Bicubic, and others)

7). Out-of-the-box support for external PNG optimizers (optipng, pngout, etc)

8). The compression and the results are comparable to those of commercial products, even higher.

9). Adaptive logarithmic tone mapping algorithm (Drago) used for HDR images

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Download FREE image optimizer: http://luci.criosweb.ro/riot/