Change Contrast of an Image

Steps to Change Contrast of an Image | OpenCV with Visual Studio in Windows 10. In this Tutorial, we are going to increase and decrease contrast of an image using OpenCV.

1. First of all, Follow this tutorial to Install & Configure OpenCV with Visual Studio 2015


2. Copy the Full Source Code to Change Contrast of an Image from here:

#include<opencv2/highgui/highgui.hpp>

using namespace cv;

int main()
{
 //Load an Image
 Mat img = imread("C:/Briefcase/Chess.jpg", CV_LOAD_IMAGE_COLOR);
 namedWindow("Image", CV_WINDOW_AUTOSIZE);
 imshow("Image", img);

 //Change Contrast Effect
 Mat imgInc;
 img.convertTo(imgInc, -1, 2, 0);  //increase (double) contrast 

 Mat imgDec;
 img.convertTo(imgDec, -1, 0.5, 0); //decrease (halve) contrast

 namedWindow("Inc contrast", CV_WINDOW_AUTOSIZE);
 namedWindow("Dec contrast", CV_WINDOW_AUTOSIZE);

 imshow("Inc contrast", imgInc);
 imshow("Dec contrast", imgDec);

 //Wait Key press
 cvWaitKey(0);

 //destroy windows
 destroyAllWindows();
 return 0;
}

OR
Get ChangeContrast.cpp from Github:
Download ChangeContrast.cpp


3. Paste full source code and Run it (Ctrl+F5 or F5).

OUTPUT

Load Image OpenCV

Increase Contrast of an Image - OpenCV

Decrease Contrast of an Image - OpenCV

Explaination :
Function used:
img.convertTo(imgInc, -1, 2, 0) - This function can process images and increase(double) contrast.
img.convertTo(imgDec, -1, 0.5, 0) - This function can process images and decrease(halve) contrast.

• 1^st parameter is the output matrix.
• 2^nd parameter is Depth of the output image. If rtype is negative, output type is same as the input type.
• 3^rd parameter is the multiplication or scaling factor, every pixel will be multiplied by this value.
• 4^th parameter is delta factor added to the scaled values.

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