Creating a custom splash image

[Pander]

Werner,

I've tried this from svn:

pngtopnm "${1:-System_boot.png}" |
  pnmquant -fs 256 |
  ppmtobmp -bpp=8 |
  gzip -9 >"${2:-splash.bmp.gz}"

but it leads to

pnmcolormap: making histogram...
pnmcolormap: 5542 colors found
pnmcolormap: choosing 256 colors...
pnmremap: EOF / read error reading magic number
pnmremap failed, rc=256
ppmtobmp: EOF / read error reading magic number

then I've tried this, which is somewhat the same but without the pipeline:

pngtopnm splash.png > splash.pnm
pnmquant -fs 256 splash.pnm > splash.ppm
ppmtobmp -bpp=8 splash.ppm > splash.bmp
gzip -f9 splash.bmp

and runs without errors but results in an upside down splash of which I
see four images at once and disappears rather quickly because it is not
in the correct format.

Can you tell me what is the best and failsafe method for creating a
custom splash image?

Thanks,

Pander