Instructions:

Create a boot image in gimp (480x800 24bit RGB color) and save as "C source code header".
Edit makebootlogo.cpp to include the path to the newly created "C source code header" file.

Run the createLogos.sh script:
./createLogos.sh

Copy the file into the Kernel's source path:
cp logo_rgb24_wvga_portrait_custom.h ../Kernel/drivers/video/samsung/logo_rgb24_wvga_portrait.h

Compile your kernel as usual.

Look to the dual-binaries branch if you plan on replacing the charge image.