# Pastebin BMpR1PCe
block convolute_greyscale(clock<rising,56e6>, enable, unsigned<6>[3] input) => (register unsigned<6>[3] output) {
  int i = 0, j = 0, k = 0;

  stream2d<unsigned<6>,5,5,1024> greyscale;
  //Convert pixel to greyscale, and push it into the stream
  greyscale << ((input[0] + input[1] + input[2]) / 3);

  //5x5 sobel matrices
  signed<5>[5][5] m1 = {{1, 2, 0, -2, -1},
                        {4, 8, 0, -8, -4},
                        {6, 12, 0, -12, -6},
                        {4, 8, 0, -8, -4},
                        {1, 2, 0, -2, -1}};

  signed<5>[5][5] m2 = {{-1, -4, -6, -4, -1},
                        {-2, -8, -12, -8, -2},
                        {0, 0, 0, 0, 0},
                        {2, 8, 12, 8, 2},
                        {1, 4, 6, 4, 1}};
  //convolute with horizontal and vertical sobel filters
  signed<16> sum1 = 0, sum2 = 0;
  for(j = 0; j < 5; j++) {
    for(k = 0; k < 5; k++) {
      sum1 += greyscale[j][k] * m1[j][k];
      sum2 += greyscale[j][k] * m2[j][k];
    }
  }
  //take the absolute value of both sums
  if(sum1 < 0) {
    sum1 = 0-sum1;
  }
  if(sum2 < 0) {
    sum2 = 0-sum2;
  }
  //add the absolute values of the two convolution results,
  //and normalise by dividing by 32
  unsigned<9> sum = (sum1 + sum2) >> 5;
  unsigned<6> result;
  //clamp the output value to 63
  if(sum > 63) {
    result = 63;
  } else {
    result = sum;
  }

  for(i = 0; i < 3; i++) {
    output[i] = result;
  }
}