Show semi-transparent image on top of other JPEG

[Mike London]

Does anyone have an example showing how to put a semi-transparent image (JPEG) on top of another JPEG image?
The effect would be a type of watermark.
Thanks in adavnce.
-- Mike

[Nathan Pruett]

Take a look at the code I posted in this thread. I posted a small watermarking application I made. It uses text that can be partially transparent, but the general idea is the same.

[Mike London]

Hi Nathan,
Yes, you posted that code to my earlier message. Your code is excellent! However, because I'm new to graphics programming, I found it difficult to extract what I needed from your cool code.
I bought the "Java 2D API" book, but have found it (***VERY***) slow going.
What I'm trying to do (which may actually be in your code)is the following:
1. Open a JPEG file that has a background image.l
2. Open another JPEG file that has a "watermark" image.
3. Write the watermark image onto the background iamge (using some kind of "transparency setting")
If you could take a quick look at the code I've come up with so far and make some suggestions, I would REALLY appreciate it. <s>
I really appreciate your replies.
-- Mike
package combinetwojpegimages;
import java.io.*;
import javax.imageio.*;
import java.awt.image.BufferedImage;
import java.awt.geom.AffineTransform;
import java.awt.*;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGEncodeParam;
import com.sun.image.codec.jpeg.JPEGImageDecoder;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

public class combine
{
public static void main (String args[])
{
File f1 = new File(args[0]);
BufferedImage biOne;
BufferedImage biTwo;
BufferedImage bOutput=null;
Graphics goutPut = null;
// create JPEG image encoder to write to the output file to.
OutputStream outStream = new FileOutputStream("outFile.jpg");
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(outStream);

// Define background image which we'll put the foreground image on top of
InputStream backGroundImage = new FileInputStream(new File(args[0]));
JPEGImageDecoder decoder = JPEGCodec.createJPEGDecoder(backGroundImage);
BufferedImage imageBack = new BufferedImage(40,30,BufferedImage.
TYPE_INT_RGB);
// Define foreground image -- will be partially transparent.
InputStream foreGroundImage = new FileInputStream(new File(args[1]));
JPEGImageDecoder decoder2 = JPEGCodec.createJPEGDecoder(foreGroundImage);
BufferedImage imageFore = new BufferedImage(40,30,BufferedImage.
TYPE_INT_ARGB);
try
{
// getGraphics() creates an offscreen (only) graphics workarea.
Graphics inputBackground = imageBack.getGraphics();
Graphics inputForeground = imageFore.getGraphics();

// create a temp buffered image workspace
BufferedImage tmp = new BufferedImage(50,50,BufferedImage.TYPE_INT_RGB);
Graphics gOut = tmp.createGraphics();
// start of writing imageFore onto imageBack using temp file tmp
// making the imageFore semi-transparent.


// End of writing mageFore onto imageBack using temp file tmp
// making the imageFore semi-transparent.

encoder.encode(tmp);
}
catch (Exception e)
{
System.out.println(e.getMessage());
}
// Do output of image below.
try
{
JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(encoder);
param.setQuality((float)1.0, true);
encoder.encode(encoder, param);
InStream.close();
outStream.flush();
outStream.close();
}
catch (Exception e)
{
System.out.println(e.getMessage());
}
}
}

[Nathan Pruett]

Ok... here's some code that works... it uses ImageIO, because it's easier to use, and is now standard with JDK 1.4... the com.sun JPEG stuff was always "unofficial". I put in lots of comments, so it should be easy to follow what I did. There's probably some better way to do this with BufferedImageOp, but this was just a quick solution...

import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStream;
 
import javax.imageio.ImageIO;
 
public class combine {
  
    public static void main ( String args[] ) {
        try {
            // Create output file
            OutputStream outStream = new FileOutputStream( "outFile.jpg" );
            
            // Load specified foreground and background JPEGs
            BufferedImage fgImage = ImageIO.read( new File( args[1] ) );
            BufferedImage bgImage = ImageIO.read( new File( args[0] ) );
            
            // Create a temporary BufferedImage for transparency.
            // Need to create it with TYPE_INT_ARGB so that it will have 
            // support for alpha transparency, which JPEGs do not have.
            BufferedImage tmpImage = new BufferedImage( fgImage.getWidth(), fgImage.getHeight(), BufferedImage.TYPE_INT_ARGB );
            Graphics gOut = tmpImage.createGraphics();
            
            // draw the foreground image on the temporary image
            gOut.drawImage( fgImage, 0, 0, null );
            gOut.dispose();
            
            // this block takes the temporary image,
            // grabs each pixel's red, green, blue, and alpha values,
            // messes with them, and writes it back out.
            int width = tmpImage.getWidth();
            int height = tmpImage.getHeight();
            int[] pixels = new int[ width * height ];
            pixels = tmpImage.getRGB( 0, 0, width, height, pixels, 0, width );
            for ( int i = 0; i < pixels.length; i++ ) {
                Color c = new Color( pixels[i] );
                int a = c.getAlpha();
                int r = c.getRed();
                int g = c.getGreen();
                int b = c.getBlue();
                // set alpha value to 65...
                // that means image is 65% transparent.
                c = new Color( r, g, b, 65 );
                pixels[i] = c.getRGB();
            }
            tmpImage.setRGB( 0, 0, width, height, pixels, 0, width );
            
            // paste the now transparent image onto the background.
            Graphics bgc = bgImage.createGraphics();
            bgc.drawImage( tmpImage, 10, 10, null );
            bgc.dispose();
            
            // Save the new composite image
            ImageIO.write( bgImage, "JPEG", outStream );
            outStream.close();
        }
        catch ( Exception x ) {
            x.printStackTrace();
        }
    }
} 

[Mike London]

Thanks!!
-- Mike

[Mike London]

Nate,
I wanted to post another thank you reply for the code you posted above.
Your code worked great and taught me a lot about graphics, which I'm totally new to.
Thank you, again, very, very much!
-- Mike