Image Processing in Java | Set 12 ( Contrast Enhancement )

In this article we will learn how to enhance contrast of an image using OpenCV library. In order to enhance contrast histogram equalization techniques are used.
For more information about histogram equalization techniques refer to this paper.

At first we need to setup OpenCV for Java, we recommend to use eclipse for the same since it is easy to use and setup. For installation refer to

Now lets understand some of the methods required for contrast enhancement.

  1. equalizeHist(source, destination) – This method resides in Imgproc package of OpenCv. source parameter is 8-bit single channel source image, and the destination parameter is the destination image
  2. Imcodecs.imread()/Imcodecs.imwrite() – These methods are used to read and write images as Mat objects which are rendered by OpenCV.




// Java program to demonstrate contrast enhancement
package ocv;
import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;
public class Main
    public static void main( String[] args )
            // For proper execution of native libraries
            // Core.NATIVE_LIBRARY_NAME must be loaded before
            // calling any of the opencv methods
            System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
            //input image
            Mat source = Imgcodecs.imread("E:\\input.jpg",
            Mat destination = new Mat(source.rows(),
                               source.cols(), source.type());
            // applying histogram equalization
            Imgproc.equalizeHist(source, destination);
            // writing output image
            Imgcodecs.imwrite("E:\\output.jpg", destination);
        catch (Exception e)
            System.out.println("error: " + e.getMessage());


Note: The code will not work in online ide since it requires image in hard drive.



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