answer_5.cpp

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

// BGR -> HSV
cv::Mat BGR2HSV(cv::Mat img){
  // get height and width
  int width = img.cols;
  int height = img.rows;

  float r, g, b;
  float h, s, v;
  float _max, _min;

  // prepare output
  cv::Mat hsv = cv::Mat::zeros(height, width, CV_32FC3);

  // each y, x
  for (int y = 0; y < height; y++){
    for (int x = 0; x < width; x++){
      // BGR -> HSV
      r = (float)img.at<cv::Vec3b>(y, x)[2] / 255;
      g = (float)img.at<cv::Vec3b>(y, x)[1] / 255;
      b = (float)img.at<cv::Vec3b>(y, x)[0] / 255;

      _max = fmax(r, fmax(g, b));
      _min = fmin(r, fmin(g, b));

      // get Hue
      if(_max == _min){
	      h = 0;
      } else if (_min == b) {
	      h = 60 * (g - r) / (_max - _min) + 60;
      } else if (_min == r) {
	      h = 60 * (b - g) / (_max - _min) + 180;
      } else if (_min == g) {
	      h = 60 * (r - b) / (_max - _min) + 300;
      }

      // get Saturation
      s = _max - _min;

      // get Value
      v = _max;

      hsv.at<cv::Vec3f>(y, x)[0] = h;
      hsv.at<cv::Vec3f>(y, x)[1] = s;
      hsv.at<cv::Vec3f>(y, x)[2] = v;
    }
  }
  return hsv;
}


// HSV -> BGR
cv::Mat HSV2BGR(cv::Mat hsv){
  // get height and width
  int width = hsv.cols;
  int height = hsv.rows;

  float h, s, v;
  double c, _h, _x;
  double r, g, b;

  // prepare output
  cv::Mat out = cv::Mat::zeros(height, width, CV_8UC3);

  // each y, x
  for (int y = 0; y < height; y++){
    for (int x = 0; x < width; x++){

      h = hsv.at<cv::Vec3f>(y, x)[0];
      s = hsv.at<cv::Vec3f>(y, x)[1];
      v = hsv.at<cv::Vec3f>(y, x)[2];

      c = s;
      _h = h / 60;
      _x = c * (1 - abs(fmod(_h, 2) - 1));

      r = g = b = v - c;
      
      if (_h < 1) {
        r += c;
        g += _x;
      } else if (_h < 2) {
        r += _x;
        g += c;
      } else if (_h < 3) {
	  g += c;
	  b += _x;
      } else if (_h < 4) {
	  g += _x;
	  b += c;
      } else if (_h < 5) {
	  r += _x;
	  b += c;
      } else if (_h < 6) {
	  r += c;
	  b += _x;
      }

      out.at<cv::Vec3b>(y, x)[0] = (uchar)(b * 255);
      out.at<cv::Vec3b>(y, x)[1] = (uchar)(g * 255);
      out.at<cv::Vec3b>(y, x)[2] = (uchar)(r * 255);
    }
  }

  return out;
}

// inverse Hue
cv::Mat inverse_hue(cv::Mat hsv){
  int height = hsv.rows;
  int width = hsv.cols;

  for(int y = 0; y < height; y++){
    for(int x = 0; x < width; x++){
      hsv.at<cv::Vec3f>(y, x)[0] = fmod(hsv.at<cv::Vec3f>(y, x)[0] + 180, 360);
    }
  }

  return hsv;
}


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

  // BGR -> HSV
  cv::Mat hsv = BGR2HSV(img);

  // Inverse Hue
  hsv = inverse_hue(hsv);

  // Gray -> Binary
  cv::Mat out = HSV2BGR(hsv);

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

  return 0;
}