I see now that this is what they purport to do. However I still maintain that the presentation is dishonest. Showing a comparison at 25% scale gives the impression that the tool is better at choosing "nearly lossless" setting than it really is. Look at the dog image, which on their demo appears to be identical to the original.
Now look at it at 100% scale: http://imgur.com/z12mHnd . Block artifacts galore. Now sure, it may still do a better job than just choosing a constant quality setting and applying it across the board. But the demo doesn't show us that. It doesn't even make the right kind of comparison.
What we need is a comparison of choosing a single quality level, and using JPEGmini. To be useful, here's the kind of demo we'd need to see.
On the right side: five JPEGs saved with JPEGmini, having a total file size of X, shown at 100% resolution.
On the left side: five JPEGs saved with a constant quality setting, chosen so that the total file size is X, also shown at 100% resolution.
Then we'd honestly know whether the program is worth using.
My guess? Probably not. The train station image, for example, is so grainy that you can compress it to damn near 600KB (50% in GIMP) before the artifacts are really noticeable (and well beyond that if you scale it down to 25% afterward). So did JPEGmini's visual model detect this and cut the bitrate down accordingly? No, it decided that the image should be saved at the equivalent of 83%, making the file more than twice as large as necessary. And this is on an image that was presumably handpicked as a shining example of how well the product works.
My guess is that if you just chose around a 75% quality setting and compressed all of your JPEGs that way, you'd do just as well as JPEGmini.
Now look at it at 100% scale: http://imgur.com/z12mHnd . Block artifacts galore. Now sure, it may still do a better job than just choosing a constant quality setting and applying it across the board. But the demo doesn't show us that. It doesn't even make the right kind of comparison.
What we need is a comparison of choosing a single quality level, and using JPEGmini. To be useful, here's the kind of demo we'd need to see.
On the right side: five JPEGs saved with JPEGmini, having a total file size of X, shown at 100% resolution.
On the left side: five JPEGs saved with a constant quality setting, chosen so that the total file size is X, also shown at 100% resolution.
Then we'd honestly know whether the program is worth using.
My guess? Probably not. The train station image, for example, is so grainy that you can compress it to damn near 600KB (50% in GIMP) before the artifacts are really noticeable (and well beyond that if you scale it down to 25% afterward). So did JPEGmini's visual model detect this and cut the bitrate down accordingly? No, it decided that the image should be saved at the equivalent of 83%, making the file more than twice as large as necessary. And this is on an image that was presumably handpicked as a shining example of how well the product works.
My guess is that if you just chose around a 75% quality setting and compressed all of your JPEGs that way, you'd do just as well as JPEGmini.