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−

In this chapter we are going to see how you can download an image from internet, perform some image processing techniques on the image, and then again upload the processed image to a server.

Downloading an Image

In order to download an image from a website, we use java class named URL, which can be found under java.net package. Its syntax is given below −

String website = "http://tutorialspoint.com";
URL url = new URL(website);				

Apart from the above method, there are other methods available in class URL as described briefly −

Example

The following example demonstrates the use of java URL class to download an image from the internet −

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import java.net.URL;

public class Download {

   public static void main(String[] args) throws Exception {
   
  try{
     String fileName = "digital_image_processing.jpg";
     String website = "http://tutorialspoint.com/java_dip/images/"+fileName;
     
     System.out.println("Downloading File From: " + website);
     
     URL url = new URL(website);
     InputStream inputStream = url.openStream();
     OutputStream outputStream = new FileOutputStream(fileName);
     byte[] buffer = new byte[2048];
     
     int length = 0;
     
     while ((length = inputStream.read(buffer)) != -1) {
        System.out.println("Buffer Read of length: " + length);
        outputStream.write(buffer, 0, length);
     }
     
     inputStream.close();
     outputStream.close();
     
  } catch(Exception e) {
     System.out.println("Exception: " + e.getMessage());
  }
   }
}

Output

When you execute the given above, the following output is seen.

It would download the following image from the server.

Uploading an Image

Let us see how to upload an image to a webserver. We convert a BufferedImage to byte array in order to send it to server.

We use Java class ByteArrayOutputStream, which can be found under java.io package. Its syntax is given below −

ByteArrayOutputStream baos = new ByteArrayOutputStream();
ImageIO.write(image, "jpg", baos);

In order to convert the image to byte array, we use toByteArray() method of ByteArrayOutputStream class. Its syntax is given below −

byte[] bytes = baos.toByteArray();

Apart from the above method, there are other methods available in the ByteArrayOutputStream class as described briefly −

Example

The following example demonstrates ByteArrayOutputStream to upload an image to the server −

Client Code

import javax.swing.*;  
import java.net.*; 
import java.awt.image.*;
import javax.imageio.*;
import java.io.*;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;

public class Client{
   public static void main(String args[]) throws Exception{
   
  Socket soc;
  BufferedImage img = null;
  soc=new Socket("localhost",4000);
  System.out.println("Client is running. ");
  
  try {
     System.out.println("Reading image from disk. ");
     img = ImageIO.read(new File("digital_image_processing.jpg"));
     ByteArrayOutputStream baos = new ByteArrayOutputStream();
     
     ImageIO.write(img, "jpg", baos);
     baos.flush();
     
     byte[] bytes = baos.toByteArray();
     baos.close();
     
     System.out.println("Sending image to server. ");
     
     OutputStream out = soc.getOutputStream(); 
     DataOutputStream dos = new DataOutputStream(out);
     
     dos.writeInt(bytes.length);
     dos.write(bytes, 0, bytes.length);
     
     System.out.println("Image sent to server. ");
     dos.close();
     out.close();
     
  } catch (Exception e) {
     System.out.println("Exception: " + e.getMessage());
     soc.close();
  }
  soc.close();
   }
}

Server Code

import java.net.*;
import java.io.*;
import java.awt.image.*;

import javax.imageio.*; 
import javax.swing.*; 

class Server {
   public static void main(String  args[]) throws Exception{
  ServerSocket server=null;
  Socket socket;
  server = new ServerSocket(4000);
  System.out.println("Server Waiting for image");
  socket = server.accept();
  System.out.println("Client connected.");
  
  InputStream in = socket.getInputStream();
  DataInputStream dis = new DataInputStream(in);
  int len = dis.readInt();
  System.out.println("Image Size: " + len/1024 + "KB");
  
  byte[] data = new byte[len];
  dis.readFully(data);
  dis.close();
  in.close();
  InputStream ian = new ByteArrayInputStream(data);
  BufferedImage bImage = ImageIO.read(ian);
 
  JFrame f = new JFrame("Server");
  ImageIcon icon = new ImageIcon(bImage);
  JLabel l = new JLabel();
  
  l.setIcon(icon);
  f.add(l);
  f.pack();
  f.setVisible(true);
   }
}

Output

Client Side Output

When you execute the client code, the following output appears on client side −

Server Side Output

When you execute the server code, the following ouptut appears on server side −

After receiving the image, the server displays the image as shown below −