c++圖像處理之池化操作

 

池化後的圖像尺寸發生變化，計算公式如下：

思路：

1、遍歷池化後的圖像數據。

2、在原圖找到滑動窗口下對應的數據值（max、aveal等）。

以平均池化爲例，數據類型爲opencv 的mat格式：

void ave_pool(int filter_size, int padding, int stride)
{
  Mat src = imread("pic/open_image.jpg", IMREAD_COLOR);
  static int yu;
  int width = src.cols;
  int height = src.rows;
  int channels = src.channels();
  int _width = (float)(width - filter_size) / stride + 1;
  int _height = (float)(height - filter_size) / stride + 1;

  Mat out = Mat::zeros(Size(_width, _height), CV_8UC3);
  printf("w=%d,h=%d,c%d\n", _width, _height, out.channels());

  for (int j = 0; j < _height; j++)
  {
    uchar *ptrlines = out.ptr<uchar>(j);

    for (int i = 0; i < _width; i++)
    {
      for (int k = 0; k < channels; k++)
      {
        ptrlines[3 * i + k] = get_max(src, filter_size, i * stride, j * stride, k);
      }
    }
  }

  imwrite("out.jpg", out);
  imshow("answer", out);
  waitKey(0);
  destroyAllWindows();
}

uchar get_ave(Mat src, int filter_size, int x, int y, int c)
{
  float sum;

  for (int j = 0; j < filter_size; j++)
  {
    uchar *ptr = src.ptr<uchar>(y + j);

    for (int i = 0; i < filter_size; i++)
    {
      sum += ptr[(x + i) * 3 + c];
    }
  }
  uchar ave = sum / (filter_size * filter_size);

  return ave;
}

下面輸入：ave_pool(9,0,2)

 

總結：以上效果說明pool對圖像具有采樣功能，通常用於對特徵圖像進行降維（特徵壓縮）。