OptiPNG is a PNG optimizer that recompresses image files to a smaller size, without losing any information.

OptiPNG program also converts external formats (PNM, BMP, GIF, and TIFF) to optimized PNG, and performs PNG integrity checks and corrections.

NOTE: OptiPNG is licensed and released under the zlib/libpng license.

Here are some key features of "OptiPNG":

· It losslessly reduces the bit depth, the color type and the color palette of the image. This step reduces the size of the uncompressed image, which, indirectly, reduces the size of the compressed image (i.e. the size of the PNG file).
· It runs a suite of compression methods and strategies and selects the parameters that yield the smallest output file.
· It concatenates all the IDAT data in a single chunk, minimizing the overhead incurred by chunk headers and CRCs.
· It offers a suite of optimization level presets. Given the number of trials that the user is willing to run, these presets will select the range of compression parameters that are most likely to yield the smallest output.
· It offers a high degree of freedom to advanced users who can choose among many kinds of compression parameters. The optimization level presets and the custom compression parameters may be used in any combination.
· It allows advanced users to disable certain image reductions.
· It corrects integrity errors found in the input files. Bad CRCs, invalid data in ancillary chunks, incomplete PNG files, or extraneous data in IDAT, are examples of such integrity errors.
· It recognizes several external file formats: BMP, GIF, PNM (PBM, PGM, PPM), TIFF

What's New in This Release: [ read full changelog ]

· Upgraded libpng to version 1.2.36-optipng [private]
· Fixed a use-after-free error in the GIF reader.
· (Thanks to Roy Tam for the report, and to Bryan McQuade for the fix.)
· Flushed the output log to display the current trial in real time.
· This only worked on Windows in the previous version.
· (Thanks to Vincent Lefevre for the fix.)
· Fixed an error in reporting unrecognized file formats.
· (Thanks to [LaughingMan] for the report.)
· Removed the requirement to "fix" TIFF files that contain unrecognized
· metadata. (Thanks to Piotr Bandurski for the suggestion.)
· Simplified the option abbreviation rules. Option names can now be
· abbreviated to their shortest unique prefix, as in X11 applications.