Heinrich Tillack emailed me with this news:

i uploaded a small tool at http://a128.ch9.de

"tga2kmg" tool :

This utility loads 24bit TGAs and converts them into twiddled KMGs of the specified format. Creates working (!!) RGB565, ARGB4444 , ARGB1555 textures. I wrote this tool because I was sick of this non-working PNG lib and would like to have punchthru / translucent textures with alpha channel on my Dreamcast

cygwin/win32 bin+source

regards

heinrich

Thanks to Heinrich for the news.