OpenCV && C++ 05 - Change Contrast

如果你想加强一幅图像的对比度，可以给每个像素的值都乘以一个大于1的常数

\[new\_image (i, j) = image(i, j) * c\]

其中 \(c > 1\)

如果你想减弱一幅图像的对比度，可以给每个像素的值都乘以一个大于0且小于1的常数

\[new\_image (i, j) = image(i, j) * c\]

其中 \(0 < c < 1\)

Code

/*
作者：郑大峰
时间：2019年09月20日
环境：OpenCV 4.1.1 + VS2017
内容：Change Contrast
*/

#include "pch.h"
#include <iostream>
#include <opencv2/opencv.hpp>

using namespace std;
using namespace cv;

int main()
{
    Mat image = imread("claudia.png");

    if (image.empty())
    {
        cout << "Could not open or find the image" << endl;
        cin.get();
        return -1;
    }

    Mat imageContrastHigh2;
    image.convertTo(imageContrastHigh2, -1, 2, 0); //increase the contrast by 2

    Mat imageContrastHigh4;
    image.convertTo(imageContrastHigh4, -1, 4, 0); //increase the contrast by 4

    Mat imageContrastLow0_5;
    image.convertTo(imageContrastLow0_5, -1, 0.5, 0); //decrease the contrast by 0.5

    Mat imageContrastLow0_25;
    image.convertTo(imageContrastLow0_25, -1, 0.25, 0); //decrease the contrast by 0.25


    //Defining window names for above images
    String windowNameOriginalImage = "Original Image";
    String windowNameContrastHigh2 = "Contrast Increased by 2";
    String windowNameContrastHigh4 = "Contrast Increased by 4";
    String windowNameContrastLow0_5 = "Contrast Decreased by 0.5";
    String windowNameContrastLow0_25 = "Contrast Decreased by 0.25";

    //Create and open windows for above images
    namedWindow(windowNameOriginalImage, WINDOW_NORMAL);
    namedWindow(windowNameContrastHigh2, WINDOW_NORMAL);
    namedWindow(windowNameContrastHigh4, WINDOW_NORMAL);
    namedWindow(windowNameContrastLow0_5, WINDOW_NORMAL);
    namedWindow(windowNameContrastLow0_25, WINDOW_NORMAL);

    //Show above images inside the created windows.
    imshow(windowNameOriginalImage, image);
    imshow(windowNameContrastHigh2, imageContrastHigh2);
    imshow(windowNameContrastHigh4, imageContrastHigh4);
    imshow(windowNameContrastLow0_5, imageContrastLow0_5);
    imshow(windowNameContrastLow0_25, imageContrastLow0_25);

    waitKey(0); // Wait for any key stroke

    destroyAllWindows(); //destroy all open windows

    return 0;
}

Result

Explanation