OpenCV : Make sharpen image color

We sometimes take pictures where there is no light, so the pictures come out dark. This means it did not have a wide range of colors. For example, an image with a minimum value of 20 and a maximum value of 100 will be dark. So we need to wide the color range of the image 0 to 255.

The full code is as follows.

#include <iostream>
#include <opencv2/opencv.hpp>
using namespace cv;
using namespace std;

void meanVal(Mat* inputArray){
    double minVal, maxVal;
    minMaxIdx(*inputArray, &minVal, &maxVal); //get min, max value of matrix    

    double ratio = (maxVal - minVal)/255; 
    *inputArray = (*inputArray - minVal)/ratio; // wide image range    

    cout << minVal << "," << maxVal << endl;
}

int main() {
    Mat img = imread("./res/woman.png");
    imshow("origin", img);
    vector<Mat> bgr_img;
    split(img, bgr_img); // split matrix to 3 channels (Blue, Green, Red)    

    meanVal(&bgr_img[0]);
    meanVal(&bgr_img[1]);
    meanVal(&bgr_img[2]);

    merge(bgr_img, img); // merge three channels to on matrix
    img = img + Scalar(10, 20, 20); // add warm color to img    

    imshow("result", img);
    waitKey(0);
    return 0;
}

• Split matrix by channel

void split(InputArray mat, OutputArrayOfArrays mv)

• Merge channels to one matrix

void merge(InoutArraysOfArrays mv, OutputArray mat)

• Get min, max value of matrix

void minMaxIdx(InputArray src, double* minVal, double* maxVal = 0, int* minIdx = 0, int* maxIdx = 0, InputArray mask = noArray());