Losing Pixel Dithering Effect when Game Runs

Hello, I'm just starting work on a vertical shooter with a scrolling background. I created a very long (400 x 2400px) png image that is supposed to scroll. The image features a pixel dithering effect for shading:



The issue I have is when I run my game with these settings I get this instead:



I've tried turning off HDR on my monitor. Googling around to see if anyone has a...

Losing Pixel Dithering Effect when Game Runs