A full-featured splash screen seems to be a bit complicated
However, if you just want to hide all console output during boot, you can make the following changes to /boot/cmdline.txt, so that just the raspberry logo is shown during boot and nothing else:
- Replace "console=tty1" by "console=tty3" to redirect boot messages to the third console.
- Add "loglevel=3" to disable non-critical kernel log messages.
- Hide the text cursor: "vt.global_cursor_default=0".
To see the console output anyway, just press Alt+F3 during or after boot.
You might also want to comment out the line in /etc/inittab that starts a getty process (the login prompt) on tty1.