Rendering 4k images -- png or jpg


I have a customer that says the images – png and jpg – rendered by the nVidia Apps look better than the ones rendered by my App. These are full screen 4k images.

He says on the device the nVidia app renders the images first as blurry but then they fill in in high resolution as a series of blocks whereas the ones rendered by my App look down sampled.

Does anyone know anything about this? Do we need to do something special on Shield TV to render images at 4K resolution?