There another great tool by leecherman for those custom bubbles. So you can make they look just like you want them too, with the simple Pboot creator for the PSVita.
Read me: Just Drag’n’Drop *.ISO, *.PBP, *.SFO files to the first input field to fetch the files from it. Press on the Save icon to Save the new created PBOOT.PBP file.
The supported image files are:
*.PNG, *.JPG, *.JPEG, *.BMP, *.GIF
If the image dimension larger\smaller than the default size ( 144×80, 80×80 )
This tool will automatically resize it.