Black Bird Image Optimizer is a commercial tool that is able to optimize the size of PNG and JPG files. Although the tool uses color quantization, specifically harnessing compression tools pngquant and jpegtran. With these it is able to reduce the number of colors in an image, while maintaining the overall visual construction. The resulting image does look very similar to the original, however it does not produce lossless compression.

The app is fairly straightforward to use. Simply start it and hit 'Upload File' then select a target file that is subsequently displayed in the 'Before' window. In a few seconds a reduced version of your image is displayed in the 'Optimized' window with the reduced file size.

Color quantization reduces the number of colors in an image while maintaining its overall visual construction. Depending on the file type, this can reduce the file size of the image.

Black Bird Image Optimizer also tries to find the best colortype for a PNG file. At the beginning of this process, it should transform the RGB area that let it to choose the optimal colortype with more precision.

The app also lets you apply some effects to enhance the image further, such as adding a blur effect, or tweaking brightness and contrast.

Overall, Black Bird Image Optimizer has a restrictive trial policy that only lets you work with one image at a time, and you can only optimise 20 images before you have to pay for a licence fee. So, if you need to reduce the size of a few images and want to test a out a simple app, then Black Bird Image Optimizer should be worthy of your time.