How to address a cv::cuda::GpuMat variable, passed to kernel as cv::cudaPtrStepSz?

C++
1

Hi!
I have an BGR image in device(cv::cuda::GpuMat) and I am passing this variable to my custom kernel function as cv::cuda::PtrStepSz. Below is the code of kernel.

__global__ void hist_mod(
                            int* BMap, int* GMap, int* RMap,
                            cv::cuda::PtrStepSz<uchar> input,
                            unsigned char* output, 
                            int color_width_step,
                            int rows, int cols
                        ){
    
    int xidx = threadIdx.x + blockIdx.x*blockDim.x;
    int yidx = threadIdx.y + blockIdx.y*blockDim.y;

    if(xidx < cols && yidx < rows){
        const int color_tid = yidx * color_width_step + xidx * 3;  // location of the pixel in the image 3d
        // const int gray_tid = yidx * cols + xidx;  // location of the pixel in the image 2d
        
        const unsigned char blue = input(yidx, xidx)[0];
        const unsigned char green = input(yidx, xidx)[1];
        const unsigned char red = input(yidx, xidx)[2];

        output[color_tid] = (uchar)BMap[(int)blue];
        output[color_tid + 1] = (uchar)GMap[(int)green];
        output[color_tid + 2] = (uchar)RMap[(int)red];

    }
}

My query is, as a 3 channel BGR Image, how to address inside the kernel?

        const unsigned char blue = input(yidx, xidx)[0];
        const unsigned char green = input(yidx, xidx)[1];
        const unsigned char red = input(yidx, xidx)[2];
2

Unless I’m missing something it should be

const unsigned char blue = input(yidx, xidx);
const unsigned char green = input(yidx, xidx+1);
const unsigned char red = input(yidx, xidx+2);