download here (FEB 20 2012)
Old version (APR 2010)
This archive contains:
XSIZEQ - a program for resizing 24-bit BMP files at the command line
TENSAI73 - does color reduction of 24-bit BMPs and attempts to optimize the output for the target hardware. Various color depths are supported, multiple palettes, and dithering (every other pixel, Floyd-Steinberg, or none at all). Partial support for scanline color changes, and automatic palette assignment (this part was rewritten).
KYOUJIN - simulates YUV or YJK color space with chroma subsampling and dithering.
FreeBASIC source and win32 binaries are included, as well as palette definitions for C64, TMS9918, NES, and Atari CTIA. Finally, there is a batch file MAKEALL.BAT which can be used to convert one reference .BMP to a series using a wide range of settings
Actually getting the images to display on other hardware is a separate matter! But, images containing 256 or fewer colors can be saved as 8-bit palettized BMPs. The palette is also dumped to TPALETTE.TXT and TPALETTE.PAL, palette maps are written to TPALMAP.BIN, and the 16-bit color index for each pixel is written to TINDEX.BIN
C64 multicolor Atari 5 color TMS9918
NES MSX2 MSX2+
Genesis Master System
Recently, I've been working on moving this functionality into a new menu-driven program, where results can be seen immediately as settings are adjusted. imgtool demo (many of the options are not yet implemented)