I'm not exactly sure of that...but the image I made is lower than the originaly provided one and works fine for me...1.13kb PNG format I think it is...
What I did was simply make a Monochrome bitmap image in paint (black & white colors only) and later save it as a PNG image so I could add another color (in this case dark red) instead of white.
Remember, he states in the readme that only basic name_plate backgrounds will work for now, because more elaborate ones seem to require the firmware spoof hack, which is currently disabled for SE users, cause it'll lead you to partial bricking and having to recover your fw. Hope this helps.
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