Preview not showing actual size

I'm on a 15" 2017 MacBook Pro with a 4k secondary display and every time I preview an image that has let's say a full-HD resolution (1920x1080) it previews in "actual size" much larger and pixelated. That's very annoying because I use the spacebar preview and the preview app all the time and need to see the images non-pixelated in real size. I already tried changing the preview options for the actual size but it doesn't fix it.

Any help is appreciated!