I didn't find much for instructions on making custom backgrounds. So, if this is redundant I apologize. But, it's actually instruction on fixing the aspect ratio for your backgrounds.
Model: AVIC-8000NEX
Problem: Backgrounds appear stretched
Cause: Display pixels are not 1:1 ratio Resolution: Squish image in the opposite direction before upload
Pretty much the first thing I did after installing my stereo was change the splash screen. I wanted the Nissan hamburger logo to load when I turned my car on. Unfortunately, that nice circular logo was showing up as an oval.
Quick mat