Re: Image Thinning using JAVA

From:

Knute Johnson <nospam@knutejohnson.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 26 Jun 2012 22:04:25 -0700

Message-ID:

<jse48p$pku$1@dont-email.me>

On 6/26/2012 8:15 PM, John B. Matthews wrote:

In article <jsd9em$hur$1@dont-email.me>,
Knute Johnson <nospam@knutejohnson.com> wrote:

     public static BufferedImage convertToGray(BufferedImage image) {
         BufferedImage gray = new BufferedImage(image.getWidth(),
             image.getHeight(), BufferedImage.TYPE_BYTE_GRAY);
         ColorConvertOp op = new ColorConvertOp(
             image.getColorModel().getColorSpace(),
             gray.getColorModel().getColorSpace(), null);
         op.filter(image, gray);
         return gray;
     }

Thanks for weighing in on this. Your approach has always worked
flawlessly on JPG images, but I had trouble with a PNG file: the result
was unusually dark, and a subsequent call to gray.getGrapics() failed.
I'd welcome any insight you can offer.

You can use the same technique as above with an AffineTransformOp, as
John Matthews mentioned, to scale an image.

I had good results with AffineTransformOp.TYPE_NEAREST_NEIGHBOR for
down sampling:

<https://sites.google.com/site/trashgod/scaled>

As recently suggested by BGB:

<https://groups.google.com/d/msg/comp.lang.java.programmer/zH_xK85o2mA/V--P6ruObwUJ>

You got me interested on that one. I made a really simple test program
because of time constraints.

What I found was that if you just did a ColorConvertOP to a PNG or a
JPEG image, the image was in fact fairly dark. But if you then convert
that image to a compatible image it looks really good in gray scale.

Here's the simple code.

package com.knutejohnson.test;

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.io.*;
import javax.imageio.*;
import javax.swing.*;

import com.knutejohnson.classes.ImageUtilities;

public class PNGtoGray extends JPanel implements ActionListener {
     private BufferedImage bi;

     public PNGtoGray(BufferedImage bi) {
         this.bi = bi;

         setPreferredSize(new Dimension(bi.getWidth(),bi.getHeight()));
     }

     public void actionPerformed(ActionEvent ae) {
         bi = ImageUtilities.convertToGray(bi);
         bi = ImageUtilities.convertToCompatible(bi);
         repaint();
     }

     public void paintComponent(Graphics g) {
         g.drawImage(bi,0,0,null);
     }

     public static void main(final String[] args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 try {
                     BufferedImage bi = ImageIO.read(new File(args[0]));
                     JFrame f = new JFrame("PNGtoGray");
                     f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                     PNGtoGray ptg = new PNGtoGray(bi);
                     f.add(ptg,BorderLayout.CENTER);
                     JButton b = new JButton("Conver to Gray");
                     b.addActionListener(ptg);
                     f.add(b,BorderLayout.SOUTH);
                     f.pack();
                     f.setVisible(true);
                 } catch (IOException ioe) {
                     System.out.println(ioe);
                 }
             }
         });
     }
}

package com.knutejohnson.classes;

import java.awt.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.io.*;
import java.util.*;
import javax.imageio.*;
import javax.imageio.stream.*;
import javax.imageio.plugins.jpeg.*;

public class ImageUtilities {
     public static void writeJPEG(RenderedImage image, float quality,
File file)
      throws IOException {
         if (quality < 0.0f || quality > 1.0f)
             throw new IllegalArgumentException("0.0 < Quality < 1.0");
         ImageWriter writer = null;
         Iterator iter = ImageIO.getImageWritersByFormatName("JPEG");
         if (!iter.hasNext())
             throw new IOException("No Writers Available");
         writer = (ImageWriter)iter.next();
         if (file.exists())
             file.delete();
         ImageOutputStream ios = ImageIO.createImageOutputStream(file);
         writer.setOutput(ios);
         JPEGImageWriteParam iwp = new JPEGImageWriteParam(null);
         iwp.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
         iwp.setCompressionQuality(quality);
         writer.write(null,new IIOImage(image,null,null),iwp);
         ios.flush();
         writer.dispose();
         ios.close();
     }

     public static BufferedImage convertToGray(BufferedImage image) {
         BufferedImage gray = new BufferedImage(image.getWidth(),
          image.getHeight(),BufferedImage.TYPE_BYTE_GRAY);
         ColorConvertOp op = new ColorConvertOp(
          image.getColorModel().getColorSpace(),
          gray.getColorModel().getColorSpace(),null);
         op.filter(image,gray);
         return gray;
     }

     public static BufferedImage scaleImage(BufferedImage src, double sx,
      double sy, int interpolationType) {
         AffineTransformOp op = new AffineTransformOp(
          AffineTransform.getScaleInstance(sx,sy),interpolationType);
         return op.filter(src,null);
     }

     public static BufferedImage scaleImage(BufferedImage src, double sx,
      double sy, RenderingHints hints) {
         AffineTransformOp op = new AffineTransformOp(
          AffineTransform.getScaleInstance(sx,sy),hints);
         return op.filter(src,null);
     }

     public static BufferedImage convertToCompatible(BufferedImage image) {
         GraphicsEnvironment ge =
          GraphicsEnvironment.getLocalGraphicsEnvironment();
         GraphicsDevice gd = ge.getDefaultScreenDevice();
         GraphicsConfiguration gc = gd.getDefaultConfiguration();

         BufferedImage compatible =
gc.createCompatibleImage(image.getWidth(),
          image.getHeight());

         if (compatible.getType() == image.getType())
             return image;

         ColorConvertOp op = new ColorConvertOp(
          image.getColorModel().getColorSpace(),
          compatible.getColorModel().getColorSpace(),null);

         return op.filter(image,compatible);
     }
}

--

Knute Johnson