pngcrush can be used to change the color encoding of an image. For example, if an image contains 10 colors but has a color palette of 256 entries (8-bit), pngcrush can be used to reduce the color palette to a 4-bit one and truncate the palette to 10 entries. pngcrush can also change the color type of the image. For a true-color image, changing the color type from 2 to 0 converts it to greyscale. Greyscale images are generally smaller than truecolor images because, in addition to the optional alpha channel, only one 8-bit channel is used per pixel rather than three. Greyscale images are also generally smaller than paletted images because they do not need to define a color palette. For a truecolor-alpha image, changing the color type from 6 to 2 removes the alpha channel. Chunk and metadata manipulation PNG images contain chunks with information about the image, such as its resolution (the phys chunk), the time it was last modified (the tIME chunk), and textual metadata (the text chunk and its variants). With pngcrush, a user can edit or remove those ancillary chunks. See also PNGOUT Zopfli References Further reading External links pngutils for the Win32 console pngcrush fork with optimized zlib using SSE2+ instructions, developed by CloudFlare Free graphics software Free data compression software Free software programmed in C