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The correct method for utilizing the gaussian filter function in the CUDA Npp library is as follows:

1. Include the necessary headers:

#include <npp.h>
#include <nppi_filtering_functions.h>

1. Allocate and initialize the NPP image and set the ROI:

NppiSize sizeROI = { width, height };
NppiSize maskSize = { maskWidth, maskHeight };
int nBufferSize = 0;
Npp8u* pBuffer = 0;
Npp8u* pSrcDst = 0;
int nSrcDstStep = 0;
NppiPoint anchor = { maskWidth / 2, maskHeight / 2 };

nppiMalloc(&pSrcDst, nSrcDstStep * height);
nppiSet_8u_C1R(0, pSrcDst, nSrcDstStep, sizeROI);

1. Calculate the size and allocate the buffer for the filter:

nppiFilterGaussBorderGetBufferSize(sizeROI, maskSize, &nBufferSize);
cudaMalloc(&pBuffer, nBufferSize);

1. Apply the filter on the image:

nppiFilterGaussBorder_8u_C1R(pSrcDst, nSrcDstStep, sizeROI, maskSize, anchor, pBuffer);

1. Free the memory:

cudaFree(pBuffer);
nppiFree(pSrcDst);

Note that the above code assumes that you have already defined the input and output size (width and height), mask size (maskWidth and maskHeight), and source/destination step (nSrcDstStep).