gif2png is a simple command-line utility to convert images from GIF to PNG format. It automatically preserves transparency, interlacing and text comments, and it can do multiple images in one command (e.g., gif2png *.gif). The distribution also includes a web2png script that can be used to convert an entire web tree; it calls gif2png to do image conversions, then patches IMG SRC tags correctly in referring pages.
pngcrush is an excellent batch-mode compression utility for PNG images. Depending on the application that created the original PNGs, it can improve the file size anywhere from a few percent to 40% or more (completely losslessly). The utility also allows specified PNG chunks (e.g. text comments) to be inserted or deleted, and it can fix incorrect gamma info written by Photoshop 5.0 as well as the erroneous iCCP chunk written by Photoshop 5.5.
This is a simple command-line utilitiy to convert images from TIFF to PNG format. It is primarily useful in dealing with TIFF images that contain alpha channels (transparency information), since the NetPBM suite is (currently) ill-suited for such conversions. A few test images are included.
glbmp is a lightweight and portable partial glaux replacement, providing auxDIBImageLoad and related device-independent bitmap image loading functionality. At the basic level, it's a flexible bitmap loader and decoder that can be used anywhere the color data of a bitmap is required. It supports uncompressed monochrome, 16 color, 256 color, and 24-bit bitmap files of any size, and allows for flexible output formats.