Slight difference between original image from OpenCV (HTTP) and DeepStream gRPC

[fanzh]

1. In DeepStream, the format after decoding is NV12. In nvinferserver, the input format will be converted to RBA with NvBufSurfTransformAsync() for normalization.
2. regarding my test, I mean, maybe the format conversion causes the accuracy loss. in my test, the input format is RGBA. in python backend, the R,G,B data is still the same with intput. you can dump the intermediate data to compare. Here is the faq Dump NV12 NvBufSurface into a YUV file. regarding nvvideoconvert, nvvideoconvert support more format conversion in latter versions, but these formats are not used in your python code.