pngcrush is a free and open-source command-line utility for optimizing PNG image files.

The main purpose of pngcrush is to reduce the size of the PNG IDAT data stream by trying various combinations of compression methods and delta filters.

The main use of pngcrush is for reducing the size of the image data contained in the IDAT section.

[3] pngcrush compresses the image with multiple different combinations and then stores the smallest of the resulting files.

pngcrush, when told, will also losslessly reduce the bit-depth of images or apply a color palette when possible if doing so results in a smaller file size.