Linear Color Gradient in openCV

Question

i am trying to create gradient of two colors like Photoshop. r,g,b of two colors is input and result will be the Mat of gradient. I tried it like for 5 hours at least and i could not find exact effect as of the Photoshop. I tried to create my own formula (as i could not find any on the web), by changing RGB to HSV and then adding the difference of hue, with respect to the total number of rows, to each row of Mat with and also decreasing intensity to the center of image and then increasing it again. The code is self explanatory.

Additionally if anyone can tell me the exact formula for creating a gradient it will be really helpful.

here is how Photoshop gradient looks like

and this is what i get from my code

 int r1, g1, b1, r2, g2, b2;

 r1 = 255;
 g1 = 0;
 b1 = 0;
 r2 = 0;
 g2 = 255;
 b2 = 0;

 Mat input = imread("img.jpg");
 Mat color1(input.size(), input.type());
 Mat color2(input.size(), input.type());

 vector<Mat> bgr1;
 vector<Mat> bgr2;

 split(color1, bgr1);
 bgr1[0] = b1;
 bgr1[1] = g1;
 bgr1[2] = r1;
 merge(bgr1, color1);

 split(color2, bgr2);
 bgr2[0] = b2;
 bgr2[1] = g2;
 bgr2[2] = r2;
 merge(bgr2, color2);

 vector<Mat> hls1;
 vector<Mat> hls2;

 cvtColor(color1, color1, CV_BGRA2BGR);
 cvtColor(color1, color1, CV_BGR2HSV);
 split(color1, hls1);

 cvtColor(color2, color2, CV_BGRA2BGR);
 cvtColor(color2, color2, CV_BGR2HSV);
 split(color2, hls2);

 double h1 = hls1[0].at<uchar>(0, 0);
 double h2 = hls2[0].at<uchar>(0, 0);
 double dif = (h2 - h1) / input.rows;
 double h = h1;

 double halfL = 255 / 2;
 double halfR = input.rows / 2;
 double ldif = halfL / halfR;
 double l = 255;
 bool isHalf = false;

 for (int i = 0; i < input.rows; i++)
 {
  for (int j = 0; j < input.cols; j++)
  {
   hls1[0].at<uchar>(i, j) = h;
   hls1[2].at<uchar>(i, j) = l;
  }


  if (isHalf == false){
   l -= ldif;
  }
  else{
   l += ldif;
  }

  if (i < input.rows * 0.40)
  {
   h += dif * 0.40;
  }
  else if (i < input.rows * 0.60)
  {
   h += dif * 3;
  }
  else
  {
   h += dif * 0.40;
  }

  if (i >= input.rows / 2)
  {
   isHalf = true;
  }
 }

 merge(hls1, color1);
 merge(hls2, color2);

 cvtColor(color1, color1, CV_HSV2BGR);
 cvtColor(color1, color1, CV_BGR2BGRA);

 cvtColor(color2, color2, CV_HSV2BGR);
 cvtColor(color2, color2, CV_BGR2BGRA);

 namedWindow("Color1", cv::WINDOW_NORMAL);
 resizeWindow("Color1", color1.size().width / 2, color1.size().height / 2);
 imshow("Color1", color1);

 waitKey(0);
 destroyAllWindows();
 system("pause");

Answer 1

I corrected my first code

It seems to be a really complex code for something that should be easier. I would do something like that.

int taille = 500;    
Mat image(taille,taille,CV_8UC3);
for(int y = 0; y < taille; y++){
   Vec3b val;
   val[0] = 0; val[1] = (y*255)/taille; val[2] = (taille-y)*255/taille;
   for(int x = 0; x < taille; x++)
      image.at<Vec3b>(y,x) = val;
}

On Micka's advice, I add a picture of the result with taille = 400;