Opencv MAX-MIN滤波器|极客教程

使用MAX-MIN滤波器来进行滤波吧。

MAX-MIN滤波器使用网格内像素的最大值和最小值的差值对网格内像素重新赋值。通常用于边缘检测。

边缘检测用于检测图像中的线。像这样提取图像中的信息的操作被称为特征提取。

边缘检测通常在灰度图像上进行。

python实现：

import cv2
import numpy as np

# Gray scale


def BGR2GRAY(img):
    b = img[:, :, 0].copy()
    g = img[:, :, 1].copy()
    r = img[:, :, 2].copy()

    # Gray scale
    out = 0.2126 * r + 0.7152 * g + 0.0722 * b
    out = out.astype(np.uint8)

    return out

# max-min filter


def max_min_filter(img, K_size=3):
    H, W = img.shape

    # Zero padding
    pad = K_size // 2
    out = np.zeros((H + pad * 2, W + pad * 2), dtype=np.float)
    out[pad: pad + H, pad: pad + W] = gray.copy().astype(np.float)
    tmp = out.copy()

    # filtering
    for y in range(H):
        for x in range(W):
            out[pad + y, pad + x] = np.max(tmp[y: y + K_size, x: x + K_size]) - \
                np.min(tmp[y: y + K_size, x: x + K_size])

    out = out[pad: pad + H, pad: pad + W].astype(np.uint8)

    return out


# Read image
img = cv2.imread("../imori.jpg").astype(np.float)

# grayscale
gray = BGR2GRAY(img)

# Max-Min filtering
out = max_min_filter(gray, K_size=3)

# Save result
cv2.imwrite("out.jpg", out)
cv2.imshow("result", out)
cv2.waitKey(0)
cv2.destroyAllWindows()

C++实现：

#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
#include <iostream>
#include <math.h>

// BGR -> Gray
cv::Mat BGR2GRAY(cv::Mat img){
  // get height and width
  int width = img.cols;
  int height = img.rows;

  // prepare output
  cv::Mat out = cv::Mat::zeros(height, width, CV_8UC1);

  // each y, x
  for (int y = 0; y < height; y++){
    for (int x = 0; x < width; x++){
      // BGR -> Gray
      out.at<uchar>(y, x) = 0.2126 * (float)img.at<cv::Vec3b>(y, x)[2] \
        + 0.7152 * (float)img.at<cv::Vec3b>(y, x)[1] \
        + 0.0722 * (float)img.at<cv::Vec3b>(y, x)[0];
    }
  }
  return out;
}

// max min filter
cv::Mat max_min_filter(cv::Mat img, int kernel_size){
  int height = img.rows;
  int width = img.cols;
  int channel = img.channels();

  // prepare output
  cv::Mat out = cv::Mat::zeros(height, width, CV_8UC1);


  int pad = floor(kernel_size / 2);

  double vmax = 0, vmin = 999, v = 0;

  // filtering  
  for (int y = 0; y < height; y++){
    for (int x = 0; x < width; x++){
      vmax = 0;
      vmin = 999;
      for (int dy = -pad; dy < pad + 1; dy++){
        for (int dx = -pad; dx < pad + 1; dx++){
          if (((y + dy) >= 0) && (( x + dx) >= 0) && ((y + dy) < height) && ((x + dx) < width)){
            v = (double)img.at<uchar>(y + dy, x + dx);
            if (v > vmax){
              vmax = v;
            }
            if (v < vmin){
              vmin = v;
            }
          }
        }
      }
      out.at<uchar>(y, x) = (uchar)(vmax - vmin);
    }
  }
  return out;
}

int main(int argc, const char* argv[]){
  // read image
  cv::Mat img = cv::imread("imori.jpg", cv::IMREAD_COLOR);

  // BGR -> Gray
  cv::Mat gray = BGR2GRAY(img);

  // max min filter
  cv::Mat out = max_min_filter(gray, 3);

  //cv::imwrite("out.jpg", out);
  cv::imshow("answer", out);
  cv::waitKey(0);
  cv::destroyAllWindows();

  return 0;
}

输入：

MAX-MIN滤波器