Recommended image format for Upfront parallax.

I'd like to ensure my parallax images are sharp and clean. I have an image I've exported as a png8, 144ppi, 99k, 1800x900 pixels (white space, mostly.) The image is optimized for web, but still looks reasonably sharp despite being a png8. However, after I've imported into Upfront as a parallax background, the image is zoomed in and pixelated. I'm viewing my page on a large 27" mac screen. Should I sized the image to 2400 pixels wide to accommodate these screen sizes?

The site is located here: http://www.iconmarketing.works - The second parallax (Web Services) is the one I'm questioning.