Direct Acces to YUV in Cuda?

hello
I want Process Only On Y Channel of YUV color format.
how can Direct Access to YUV color format In cuda Kenel in cudaYUV-NV12.cu In this https://github.com/dusty-nv/jetson-inference/blob/master/util/cuda/cudaYUV-NV12.cu??
Thanks,