Write pixel data in a grayscale image in java

Question

I am developing a project on image processing where I have to fill the digitized images of cracked paintings. I have to convert a color image to grayscale, performing some calculations on the 2D Array of the gray image and writing it back as gray image. The code for this is:

BufferedImage colorImage=ImageIO.read(new File(strImagePath));

            BufferedImage image = new BufferedImage(colorImage.getWidth(),colorImage.getHeight(),BufferedImage.TYPE_BYTE_GRAY);
            Graphics g = image.getGraphics();
            g.drawImage(colorImage, 0, 0, null);
            g.dispose();

            ImageIO.write(image,"PNG",new File("Image.PNG"));

            BufferedImage imgOriginal=ImageIO.read(new File("Image.PNG"));

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

            BufferedImage im=new BufferedImage(width,height,BufferedImage.TYPE_BYTE_GRAY);

            int arrOriginal[][]=new int[height][width];


            for(int i=0;i<height;i++)
                for(int j=0;j<width;j++)
                    arrOriginal[i][j]=imgOriginal.getRGB(j,i)& 0xFF;

            for(int i=0;i<height;i++)
                for(int j=0;j<width;j++)
                    im.setRGB(j,i,arrOriginal[i][j]);

            ImageIO.write(im,"PNG",new File("Image1.PNG"));

But the output image is very much darker, I am not getting the original image back (I have not done any changes yet).

I think there should be some changes in setRGB() statement but I don't know what.

To write image back, I have also tried:

`

BufferedImage im = new BufferedImage(width,height,BufferedImage.TYPE_BYTE_GRAY);
 WritableRaster raster = im.getRaster();
 for(int i=0;i<height;i++)
     for(int j=0;j<width;j++)
         raster.setSample(j,i,0,arrOriginal[i][j]);

`

But it also don't give me original image back.

Can anyone provide me the solution of this problem? Thanks in advance.

you should be inform that firefox and chrome does not render png with the same colors and it can come from the java rendering engine too. — Kiwy, Nov 27 '13 at 14:25
@Kiwy I am using javax.swing as my project is a stand alone project. — BK Prajapati, Nov 27 '13 at 15:15
See also http://stackoverflow.com/questions/3106269/how-to-use-type-byte-gray-to-efficiently-create-a-grayscale-bufferedimage-using — halfbit, Nov 27 '13 at 15:21

score 6 · Accepted Answer · answered Nov 27 '13 at 14:57

I don't know anything about Java-based image processing, but I do know quite a lot about image processing in general, so I will see if I can give you any ideas. Please don't shoot me if I am wrong - I am just suggesting an idea.

In a greyscale image, the red, green and blue values are all the same, i.e. Red=Green=Blue. So, when you call getRGB and do the AND with 0xff, you are probably getting the blue component only, but that is ok as the red and green are the same - because it's greyscale.

I suspect the problem is that when you write it back to create your new output image, you are only setting the blue component and not the red and green - which should still be the same. Try writing back

original pixel + (original pixel << 8 ) + (original pixel <<16)

so that you set not only the Blue, but also the Red and Green components.

Thanks for your response. Now I am getting original image back. And sorry I can't vote you up because my reputation doesn't allow me... — BK Prajapati, Nov 27 '13 at 15:19

Write pixel data in a grayscale image in java

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