PNGOUT

PNGOUT is a console-based application intended to help you easily compress and optimize PNG image files. Aside from this main function, it is capable of performing conversion operations, enabling you to process popular types of graphic formats.
Relying on powerful compression algorithms, PNGOUT aims to assist you in finding the perfect combination of parameters that can set a balance between the compression rate and the picture quality.
It only runs in the command prompt, which might be an inconvenient to those who are not accustomed with the console and the way commands are executed. Even so, the simple syntax and the instructions displayed at each run should be enough to help you figure out its functioning mode.
PNGOUT accepts multiple formats as its input, namely PNG, JPG, GIF, TGA, PCX and BMP files, but it only outputs PNG images. Since it runs exclusively in the console, it does not allow batch operations.
There are various commands that you can use in order to configure the conversion and / or compression procedure. PNGOUT can modify the color type of the input image, apply it filters, change the color bit depth and keep or remove optional chunks. Along with the selected compression strategies ('Xtreme', 'Intense', 'Longest Match', 'Huffman Only'), all these parameters have an impact on the resulting compression ratio.
There are additional options dedicated to specifying the number of block splits to use in the compression process or insert a minimum number of codes to the Huffman tables, which ensures the compatibility of the output with some PNG decoders.
PNGOUT comprises an image converter and a compression tool in a single package, offering you a fast way to generate optimized PNG images. While the lack of a user-friendly GUI might be a drawback for some, the application is easy to use for those who are a bit familiar with the console.