Making high quality GUI in unity

How can I make my main menu image quality not being destroyed without slicing it? because when I tried to place the image on the plane, the image’s quality is damage, it’s not sharp enough. I made my image on photoshop with the size of 1280x1024.

By default, Unity importer compress your image. Choose:

Texture Type: GUI
Max Size: 2048
Format: Truecolor