code for my blog post <https://superkogito.github.io/blog/DivideImageUsingOpenCv.html> a snippet for dividing image into blocks

DivideImageUsingOpenCv.cpp

/***********************************************************************
 * \file   DivideImageUsingOpenCv.cpp
 * \brief  divide image into multiple blocks using OpenCV.
 *
 * \author SuperKogito
 * \date   October 2020
 *
 * @note:
 * references and sources:
 * - https://answers.opencv.org/question/53694/divide-an-image-into-lower-regions/
 * - https://graphicdesign.stackexchange.com/questions/30008/crop-a-big-picture-into-several-small-size-pictures
 ***********************************************************************/
#include <Windows.h>
#include <opencv2/opencv.hpp>
#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include <opencv2/core/utils/filesystem.hpp>

using namespace std;
using namespace cv;

int divideImage(const cv::Mat& img, const int blockWidth, const int blockHeight, std::vector<cv::Mat>& blocks)
  {
   // Checking if the image was passed correctly
   if (!img.data || img.empty())
   {
  		std::wcout << "Image Error: Cannot load image to divide." << std::endl;
    	return EXIT_FAILURE;
   }

   // init image dimensions
   int imgWidth = img.cols;
   int imgHeight = img.rows;
   std::wcout << "IMAGE SIZE: " << "(" << imgWidth << "," << imgHeight << ")" << std::endl;

   // init block dimensions
   int bwSize;
   int bhSize;

   int y0 = 0;
   while (y0 < imgHeight)
   {
     // compute the block height
     bhSize = ((y0 + blockHeight) > imgHeight) * (blockHeight - (y0 + blockHeight - imgHeight)) + ((y0 + blockHeight) <= imgHeight) * blockHeight;

  	 int x0 = 0;
  	 while (x0 < imgWidth)
  	 {
       // compute the block height
  	   bwSize = ((x0 + blockWidth) > imgWidth) * (blockWidth - (x0 + blockWidth - imgWidth)) + ((x0 + blockWidth) <= imgWidth) * blockWidth;

  		 // crop block
  		 blocks.push_back(img(cv::Rect(x0, y0, bwSize, bhSize)).clone());

  		 // update x-coordinate
  		 x0 = x0 + blockWidth;
  	 }

  	 // update y-coordinate
  	 y0 = y0 + blockHeight;
   }
   return EXIT_SUCCESS;
  }

  int main()
  {
   // init vars
   const int blockw = 128;
   const int blockh = 128;
   std::vector<cv::Mat> blocks;

   // read png image
   Mat image = cv::imread("Lenna.png", IMREAD_UNCHANGED);
   cv::imshow("Display window", image);

   // divide image into multiple blocks
   int divideStatus = divideImage(image, blockw, blockh, blocks);

   // debug: save blocks
   cv::utils::fs::createDirectory("blocksFolder");
   for (int j = 0; j < blocks.size(); j++)
   {
     std::string blockId = std::to_string(j);
  	 std::string blockImgName = "blocksFolder/block#" + blockId + ".png";
  	 imwrite(blockImgName, blocks[j]);
   }

   return 0;
  }