Author: saqibkhan

In this chapter we learn to increase the sharpness of an image using Gaussian filter.

First we use OpenCV function GaussianBlur. It can be found under Imgproc package. Its syntax is given below −

Imgproc.GaussianBlur(source, destination, new Size(0,0), sigmaX);

The parameters are described briefly −

Further, we use OpenCV function addWeighted to apply image watermark to image. It can be found under Core package. Its syntax is given below −

Core.addWeighted(InputArray src1, alpha, src2, beta, gamma, OutputArray dst);

The parameters of this function are described below −

Apart from the GaussianBlur method, there are other methods provided by the Imgproc class. They are described briefly −

Example

The following example demonstrates the use of Imgproc and Core class to apply sharpening to an image −

import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.core.Size;
import org.opencv.highgui.Highgui;
import org.opencv.imgproc.Imgproc;

public class Main {
   public static void main( String[] args ) {
  try{
     System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
     Mat source = Highgui.imread("digital_image_processing.jpg",
     Highgui.CV_LOAD_IMAGE_COLOR);
     Mat destination = new Mat(source.rows(),source.cols(),source.type());
     Imgproc.GaussianBlur(source, destination, new Size(0,0), 10);
     Core.addWeighted(source, 1.5, destination, -0.5, 0, destination);
     Highgui.imwrite("sharp.jpg", destination);
  } catch (Exception e) {
  }
   }
}

Output

When you execute the given code, the following output is seen −

Original Image

Sharped Image

In this chapter learn how to enhance the contrast of an image using histogram equalization.

We use the OpenCV function equalizeHist() method. It can be found under Imgproc package. Its syntax is given below −

Imgproc.equalizeHist(source, destination);

The parameters are described below −

Apart from the equalizeHist() method, there are other methods provided by the Imgproc class. They are described briefly −

Example

The following example demonstrates the use of Imgproc class to enhance contrast of an image −

import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.highgui.Highgui;
import org.opencv.imgproc.Imgproc;

public class Main {

   static int width;
   static int height;
   static double alpha = 2;
   static double beta = 50;
   
   public static void main( String[] args ) {
   
  try {
     System.loadLibrary( Core.NATIVE_LIBRARY_NAME );
     Mat source = Highgui.imread("grayscale.jpg", 
     Highgui.CV_LOAD_IMAGE_GRAYSCALE);
     Mat destination = new Mat(source.rows(),source.cols(),source.type());
     
     Imgproc.equalizeHist(source, destination);
     Highgui.imwrite("contrast.jpg", destination);
     
  } catch (Exception e) {
     System.out.println("error: " + e.getMessage());
  }
   }
}

Output

When you execute the given code, the following output is seen −

Original Image

Enhanced Contrast Image

In order to convert a color image to Grayscale image, you need to read pixels or data of the image using File and ImageIO objects, and store the image in BufferedImage object. Its syntax is given below −

File input = new File("digital_image_processing.jpg");
BufferedImage image = ImageIO.read(input);	

Further, get the pixel value using method getRGB() and perform GrayScale() method on it. The method getRGB() takes row and column index as parameter.

Color c = new Color(image.getRGB(j, i));
int red = (c.getRed() * 0.299);
int green =(c.getGreen() * 0.587);
int blue = (c.getBlue() *0.114);

Apart from these three methods, there are other methods available in the Color class as described briefly −

The last step is to add all these three values and set it again to the corresponding pixel value. Its syntax is given below −

int sum = red+green+blue;
Color newColor = new Color(sum,sum,sum);
image.setRGB(j,i,newColor.getRGB());

Example

The following example demonstrates the use of Java BufferedImage class that converts an image to Grayscale −

import java.awt.*;
import java.awt.image.BufferedImage;

import java.io.*;

import javax.imageio.ImageIO;
import javax.swing.JFrame;

public class GrayScale {

   BufferedImage  image;
   int width;
   int height;
   
   public GrayScale() {
   
  try {
     File input = new File("digital_image_processing.jpg");
     image = ImageIO.read(input);
     width = image.getWidth();
     height = image.getHeight();
     
     for(int i=0; i<height; i++) {
     
        for(int j=0; j<width; j++) {
        
           Color c = new Color(image.getRGB(j, i));
           int red = (int)(c.getRed() * 0.299);
           int green = (int)(c.getGreen() * 0.587);
           int blue = (int)(c.getBlue() *0.114);
           Color newColor = new Color(red+green+blue,
           
           red+green+blue,red+green+blue);
           
           image.setRGB(j,i,newColor.getRGB());
        }
     }
     
     File ouptut = new File("grayscale.jpg");
     ImageIO.write(image, "jpg", ouptut);
     
  } catch (Exception e) {}
   }
   
   static public void main(String args[]) throws Exception {
  GrayScale obj = new GrayScale();
   }
}

Output

When you execute the given example, it converts the image digital_image_processing.jpg to its equivalent Grayscale image and write it on hard disk with the name grayscale.jpg.

Original Image

Grayscale Image

An image contains a two dimensional array of pixels. It is actually the value of those pixels that make up an image. Usually an image could be color or grayscale.

In Java, the BufferedImage class is used to handle images. You need to call getRGB() method of the BufferedImage class to get the value of the pixel.

Getting Pixel Value

The pixel value can be received using the following syntax−

Color c = new Color(image.getRGB(j, i));

Getting RGB Values

The method getRGB() takes the row and column index as a parameter and returns the appropriate pixel. In case of color image, it returns three values which are (Red, Green, Blue). They can be get as follows−

c.getRed();
c.getGreen();
c.getBlue();

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Getting Width and Height of Image

The height and width of the image can be get by calling the getWidth() and getHeight() methods of the BufferedImage class. Its syntax is given below−

int width = image.getWidth();
int height = image.getHeight();

Apart from these methods, there are other methods supported in the BufferedImage class. They are described briefly−

Example

The following example demonstrates the use of java BufferedImage class that displays pixels of an image of size (100 x 100)−

import java.awt.*;
import java.awt.image.BufferedImage;

import java.io.*;

import javax.imageio.ImageIO;
import javax.swing.JFrame;

class Pixel {
   BufferedImage image;
   int width;
   int height;
   
   public Pixel() {
  try {
     File input = new File("blackandwhite.jpg");
     image = ImageIO.read(input);
     width = image.getWidth();
     height = image.getHeight();
     
     int count = 0;
     
     for(int i=0; i<height; i++) {
     
        for(int j=0; j<width; j++) {
        
           count++;
           Color c = new Color(image.getRGB(j, i));
           System.out.println("S.No: " + count + " Red: " + c.getRed() +"  Green: " + c.getGreen() + " Blue: " + c.getBlue());
        }
     }
  } catch (Exception e) {}
   }
   
   static public void main(String args[]) throws Exception {
  Pixel obj = new Pixel();
   }
}

Output

When you execute the above example, it would print the pixels of the following image −

Original Image

Pixels Output

If you scroll down the ouput, the following pattern is seen−