Editor’s note: The following review is part of Macworld’s GemFest 2012 series. Every weekday from mid June through mid August, the Macworld staff will use the Mac Gems blog to briefly cover a favorite free or low-cost program. Visit the Mac Gems homepage for a list of past Mac Gems.

ImageOptim 1.4.0 helps not just the developers and designers who use the software, but also any of those users’ users, too. Let me explain: The free utility takes in your PNG, JPEG, and GIF files (including GIF animations) and optimizes them by shrinking their file sizes, often considerably. And it does so without affecting the image quality.

ImageOptim’s interface is Spartan but functional. Drag images onto its window or Dock icon, or click on the plus (+) button to select images from a standard Open dialog box. The app immediately starts optimizing the images, using one or more of a slew of command-line image optimization tools: PNGOUT, AdvPNG, Pngcrush, extended OptiPNG, JpegOptim, jpegrescan, jpegtran, and Gifsicle are all seamlessly integrated. ImageOptim doesn’t offer a whole lot of insight into what it’s doing, but you can mouse-over an individual image on the list to see which tool the app is using to shrink the image.

Alongside each filename, ImageOptim lists its file size (in bytes), and the percentage by which the file size was shrunk from the original. That number can vary widely depending upon your source image, but I’ve compressed some images more than 80-percent.

While I wish ImageOptim included a running total of just how much smaller all the files in a given batch are combined, that’s at worst a minor oversight. The app works efficiently, it’s brain-dead simple to use, and it does just what it promises.

[Staff writer Lex Friedman would be a billionaire if he could invent an ImageOptim for text.]

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