PNGB: GB Graphics Converter PNGB is a command line utility that converts PNG files to GBDK data definitions and code.

It can additionally generate "test code" that allows you to see (to some extent) the result of the conversion and how to use the data.

PNGB currently supports 8x8 tiles (BKG or WIN layers) and Sprites (both 8x8 and 8x16).

It also supports color pictures. If your image has 4 colors or less PNGB will generate an equivalent 15-bit palette for GBC. For images with more than 4 colors you'll have the options to let PNGB convert it to grayscale first and then attempt to match each color with one of the four shades of the original Gameboy.

Currently PNGB can only generate a single palette for the whole image, but in a future it may be able to extract multiple palettes from a single image.

You can see more details and examples in http://damnsoft.org/web/software/pngb