There are HDR compression settings in the details panel
This should provide a 16 bit depth for each Channel.
But there are some discussions about color displaying since they switched to a new color scheme for more realistic recreation of colors (I don’t know much about it)
By the way: you should add an extra alpha channel and save it as TGA with 32bit from photoshop. This way you can avoid getting this dark edge that PNG is creating in Unreal. PNG really has no Alpha Channel, it’s just an extra color that is declared as transparent and Unreal doesn’t put it out like from an image with real alpha channel. Also you may have seen some textures in Engine Content strech out from the pixels on the alpha channel covers, that gets important on Mipmapping, when low resolutions can’t be that exact with the alpha. [https://forums.unrealengine.com/filedata/fetch?id=1136878][2]