How to split image into small blocks, process on them and then join all the blocks together again?

edit

try to convert the code in this post or the code below

Mat src = imread("e:/getty-apple_large.jpg");

int width = src.cols;
int height = src.rows;
int GRID_SIZE = 100;

vector<Rect> mCells;

for (int y = 0; y < height - GRID_SIZE; y += GRID_SIZE) {
    for (int x = 0; x < width - GRID_SIZE; x += GRID_SIZE) {
        int k = x*y + x;
        Rect grid_rect(x, y, GRID_SIZE, GRID_SIZE);
        cout << grid_rect<< endl;
        mCells.push_back(grid_rect);
        rectangle(src, grid_rect, Scalar(0, 255, 0), 1);
        imshow("src", src);
        imshow(format("grid%d",k), src(grid_rect));
        waitKey();
    }
}

# Image path, number of rows 
# and number of columns 
# should be provided as an arguments
import cv2
import sys
import os


if not os.path.exists('patches'):
    os.makedirs('patches')



nRows = int(sys.argv[2])
# Number of columns
mCols = int(sys.argv[3])

# Reading image
img = cv2.imread(sys.argv[1])
#print img

#cv2.imshow('image',img)

# Dimensions of the image
sizeX = img.shape[1]
sizeY = img.shape[0]

print(img.shape)


for i in range(0,nRows):
    for j in range(0, mCols):
        roi = img[i*sizeY/nRows:i*sizeY/nRows + sizeY/nRows ,j*sizeX/mCols:j*sizeX/mCols + sizeX/mCols]
        cv2.imshow('rois'+str(i)+str(j), roi)
                cv2.imwrite('patches/patch_'+str(i)+str(j)+".jpg", roi)



cv2.waitKey()