Comment 3 for bug 1474991

Proposed a merge here: https://code.launchpad.net/~vishalrao/pantheon-greeter/fix-login-wallpaper-glitch/+merge/316812

Although, my patch addresses my hidpi scenario (scale factor > 1) and my wallpaper aspect is same as my monitor aspect of 16:9

This bug is occurring likely due to aspect ratio mismatch between wallpaper and monitor and/or mismatch in greeter scaling (fit to screen) versus gala desktop wallpaper scaling method (fit, zoom, scale, stretch).