Large TileMap in the background cutting framerate a lot


This is my first post ever here. I read everything I could find about large background images affecting performance without finding any answer what is the best way to solve this.

I done a lot of work on optimizing the game I’m working currently on and I reached ~400fps. But I didn’t expect that fps in my game will go from 400-430 to 320-330 when I added a background that is a 1024x1344 jpg image. It’s a 2.5D sidescroller. First I tried making 32x32 TileSet and made a TileMap from it and I resized it to fit the background. When I saw that it had a large impact on the performance I tried another way, to set “Pixels Per Unreal Unit” to 0.05. That gave me a background that looked sharp without artifacts made by resizing, but the performance stayed the same: I lost ~100fps or 20-25%. I tried putting a large sprite made from the same image and problem stays the same.
I’m packaging the game very often to check the performance and I learned a lot of things about what affects framerate etc. but I can’t solve this problem.

I like optimizing things and making everything as perfect as possible. I done a lot of things to help cpu and gpu be as effective as possible. For example, I have a lot of particle effects and moving actors that are on standby while the player is not close. I didn’t use EventTick or TimeLines at all. I disabled PostProcessing effects that wasn’t necessary. Even the HUD, I made it with Retainer Boxes that switch to drawing at every frame just while the animation is executing, than they go again to redrawing after every few hundred frames. And a lot of other things I couldn’t remember right now.

Does anybody have any experience or advice what is the best way to use a background image in UE4?