Question

I am writing a program to perform various operations on an image using the following code:

import java.awt.Desktop;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.awt.image.WritableRaster;
import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.imageio.ImageIO;

public class BrightnessContrast {
    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub
        int i, j, choice = 1;
        String imgName;
        boolean flag = true;

        String imagePath = "images/test.jpg";
        BufferedImage myImage = ImageIO.read(new File(imagePath));
        int height = myImage.getHeight();
        int width = myImage.getWidth();
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        final BufferedImage greyImage = new BufferedImage(width, height,BufferedImage.TYPE_BYTE_GRAY);
        Graphics grp = greyImage.getGraphics();
        grp.drawImage(myImage, 0, 0, null);
        File f2 = new File("images/BrightnessContrastTestInput.jpg");
        try {
            ImageIO.write(greyImage, "JPG", f2);
        } catch (IOException x) {
            x.printStackTrace();
        }

        while (flag == true) {
            System.out
                    .println(" 1.Brightness \n 2.Contrast \n 3.EXIT!");
            choice = Integer.parseInt(br.readLine());

            switch (choice) {
            case 1:
                //increase brightness

            case 2:
                //increase contrast
            case 3:
                flag = false;
                break;
            default:
                System.out.println("Invalid Option. Please try again.");
                break;
            }
        }
    }

    public static void ImageOperation(BufferedImage greyImage) {

        WritableRaster  myRaster = greyImage.getRaster();

        for (j = 0; j < greyImage.getHeight(); j++) {
            for (i = 0; i < greyImage.getWidth(); i++) {
                //some logic to increase contrast and brightness 
            }
        }

        File f = new File("images/"+imgName);
        try {
            ImageIO.write(greyImage, "JPG", f);
        } catch (IOException x) {
            x.printStackTrace();
        }
    }
    }

}

All the manipulations are done on the writable raster object myRaster in ImageOperation method, myRaster is created using a BufferedImage object greyImage.

Now, in the first run when i (let’s say) increase contrast of an image by a certain factor, it gives a proper result, in the second time if i apply the exact same amount of contrast it does that operation on the previously enhanced image, not the original one, thus, in the second go it gives me a higher contrast.

my question is that, is the BufferedImage object greyImage getting updated each time i increase contrast on the myRaster?

Answer 1

Looking at the source for BufferedImage, getRaster() returns a reference to the underlying raster object within the buffered image. So if you change the raster, you have effectively changed the image.

You might want to make a copy of the original image and then operate on the copy. This should preserve the original.