When you make available images on the Internet, be it embedded on a website, in documents, or by sending images as email attachments, you and the target audience often benefit from reduced file sizes. Webmasters may benefit from a fast optimized website in several ways, from improved click through rates to less visitors who close the tab before the full website has been been loaded. It also reduced the bandwidth the site needs to deliver its contents to its visitors. Bandwidth and time are also the factors when it comes to documents, email attachments and other forms of making images available to other users.
We have covered several automated solutions in the past. From the Thunderbird extension Shrunked Image Resizer, the WordPress plugin WP-Smush It to desktop applications to optimize images for websites and other purposes.
PNG Gauntlet is a desktop tool for Windows and Mac - the Windows version requires the Microsoft .Net Framework 4.0 - that can reduce the size of png files without reducing the image's quality at the same time. It combines three different tools for the purpose to create the smallest possible file size. What about other image formats? If you want, you can have them converted to the optimized png format.
The interface provides you with all the settings that you need to get started. Before you do, I'd suggest you click on Tools > Options to make sure everything is set correctly here. If you plan on working on the PC while the program compresses the images, you should consider checking the run compressors with low priority box to avoid slow downs on the system. Depending on your system, you may also, or alternatively, uncheck the preference to compress multiple files at once.
When that is out of the way you need to add an output directory where the optimized images are saved to. You can alternatively overwrite the existing files, but since you do not have an option to compare results, I'd suggest you do not the first times you use the program. Images can be dragged and dropped individually, in bulk or as folders into the interface.
A click on optimize runs the optimization of all images that you have added, and PNG Gaunlet will display the old and new image size, as well as the reduced size in percentage on the screen. In the status bar you find the total size that was saved by the operation, as well as information about the status of the operation. As you can see from the screenshot, the program is not the fastest. If you want fast, you should take a look at Riot instead which I have linked above. The program may not create the smallest file, but it does not take that long to get the images compressed and the difference is not that big that you can't make use of it.
Still, if you want the maximum then PNG Gauntlet can get that extra percentage off of the image size.