How to export with high resolution a cube render target

My problem is that I’m doing a mirror I do not like how it is with the reflection capturers, I tried it with sceneCaptureCube and turn that into a texture, the result seems great the problem is that it consumes a lot of resources and even deactivates that capture frame by frame I would like to export the HDR and use it as a texture to optimize the game. The problem is that when I export that loses quality