Real-time PSNR/SSIM computation while encoding with NVENC

Hi everyone,

I am performing HEVC video encoding on the pictures copied into the GPU memory. While running the encoder, I would like to measure the standard quality metrics PSNR & SSIM. Unlike x265 / x264 ,from NVENC documentation, I couldn’t find a configuration flag that makes these quality measurements while performing the compression. NPP has already defined the GPU accelerated quality metrics:

However, in this case, I need to access the memory location of the reconstructed raw frame (as displayed at the decoder) for the current frame that is being compressed.
Could you please guide me how to access the reconstructed frame / decoded raw frame in order compare the quality with respect to the original raw frame by feeding into the above mentioned npp functions?