How can I convert Yuv420 to BGR in gpu mode

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When I use cv::cvtColor in CPU,cvtColor(yuvImage, rgbImg, COLOR_YUV2BGR_I420);It works well.I can get a correct BGR picture But I want to use gpu accelerate this transform,I use gpu::cvtcolor to instead.I find this function don't support COLOR_YUV2BGR_I420 code.It has a code named YUV2BGR and Ycrcb2BGR,but this code need Yuv src picture 8UC3.I don`t know why.YUV420 picture in CPU it should be 8UC1,is it? How can I convert Yuv420 to BGR in gpu mode?