public static Pixel getNeighbor(Pixel[][] pixels, int row, int col, int neighborNo)
  {
    int maxRow = pixels.length - 1;
    int maxCol = pixels[0].length - 1;
    switch (neighborNo % 8)
    {
      case 0:
        return pixels[row == 0 ? row : row - 1][col];
      case 1:
        return pixels[row == 0 ? row : row - 1][col == maxCol ? col : col + 1];
      case 2:
        return pixels[row][col == maxCol ? col : col + 1];
      case 3:
        return pixels[row == 0 ? row : row - 1][col == maxCol ? col : col + 1];
      case 4:
        return pixels[row == maxRow ? row : row + 1][col];
      case 5:
        return pixels[row == maxRow ? row : row + 1][col == 0 ? col : col - 1];
      case 6:
        return pixels[row == 0 ? row : row - 1][col == maxCol ? col : col + 1];
      case 7:
        return pixels[row == 0 ? row : row - 1][col == 0 ? col : col - 1];
    }
    // this shouldn't happen
    return pixels[row][col];
  }