GfxCon was (and still is) a popular software for image format conversion on the Amiga computer. This was written at a time when images were still challenging to process because the computers had so little memory. 24bit graphics was almost impossible and only used in raytracers. Images with only 32 colors or less were still common and crude graphics modes like the HAM6/8 or EHB (Extra Half-Brite) mode on the Amiga were invented to alleviate the limitations of that time. However, these modes were difficult to handle and image processing software was actually more complex than today. GfxCon used the Median-Cut algorithm for color quantization (color-table generation) and Floyd-Steinberg dithering. Special variants were used for the HAM and EHB modes.
Another popular feature of GfxCon was that it had its own virtual memory handling built-in since neither the AmigaOS nor the processors (68000) supported virtual memory. From the feedback I got, many people still had computers with only 512kb of memory, and this was apparently one of the killer-features of GfxCon.
GfxCon was released long before the internet was widely used and was declared as Cardware (free, just send a postcard to the author, if you like it) and I received lots of postcards from all over the worlds, which I still treasure in a box. Thank you to all users! Unbelievably, today (2011), I still get emails from active GfxCon users.
It is also included in AmiKit.
There are several reviews in magazines. For example this one: