ImageMagick is a software suite to create, edit, and compose bitmap images. It can read, convert and write images in a variety of formats (about 100) including GIF, JPEG, JPEG-2000, PNG, PDF, PhotoCD, TIFF, and DPX.

Caesium Image Compressor lets you compress your pictures up to 90% without visible quality loss. Providing a simple yet effective interface with a real-time preview and multiple image processing at the same time, everyone will be able to reach the best result.

Saving images for web/email/other media with the best compression ratio and quality is a difficult task if you don’t have the right tools. Choosing the right format then choosing the right parameters are the key factors of smaller files.

FileOptimizer is a lossless file size optimizer supporting AIR, APK, APNG APPX, BMP, CBZ, DOCX, DLL, EPUB, EXE, GIF, GZ, ICO, JAR, JPEG, MNG, MP3, MPP, PNG, PPTX, ODT, OGG, OGV, PDF, PUB, SCR, SWF, TIF, VSD, WEBP, XAP, XLSX, and ZIP file formats among others.

-Combines PNGOUT, OptiPNG, and DeflOpt to create the smallest PNGs -No image quality is lost — only file size -Converts JPG, GIF, TIFF, and BMP files to PNG -Ultra-configurable

PNGGauntlet is a .NET program that uses Ken Silvermans PNGOUT, OptiPNG and DeflOpt to optimize PNG fil.

OptiPNG is a command-line PNG optimizer that recompresses image files to a smaller size, without losing any information. This program also converts external formats (BMP, GIF, PNM and TIFF) to optimized PNG, and performs PNG integrity checks and corrections.

GraphicsMagick is the swiss army knife of image processing. Comprised of 282K physical lines (according to David A. Wheelers SLOCCount) of source code in the base package (or 952K including 3rd party libraries) it provides a robust and efficient collection of tools and libraries...

pngquant is a command-line utility and a library for lossy compression of PNG images.

Oxipng is a multithreaded lossless PNG compression optimizer in Rust. It can be used via a command-line interface or as a library in other Rust programs.

Experimental, fast Web PNG/JPG optimizer which offer lossless, visually lossless or lossy compression. it performs image reductions over iterations thanks to recursive multi-processing and multithreading systems.

Minuimus is a file optimizer utility script: You point it at a file, and it makes the file smaller without compromising the file contents.

ShortPixel is arguably the top WordPress image optimization plugin: simple to set up, it can automatically optimize both your old and new images, as well as PDF files.