Why doesn't Java properly re-create this image from an InputStream?

Question

I've looked at this every way I can think... The problem is that I end up writing the PERFECT number of bytes, and the files are VERY similar - but some bytes are different. I opened the Java generated file in Scite as well as the original, and even though they are close, they are not the same. Is there any way to fix this? I've tried doing everything possible - I've used different wrappers, readers, writers and different methods of taking the byte array (or taking it as chars - tried both) and making it into a file.

The image in question, for the test, is at http://www.google.com/images/srpr/nav_logo13.png. Here's the code:

import java.awt.Image;
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

import javax.imageio.ImageIO;

public class ImgExample
{

    private String address = "http://www.google.com";
    /**
     * Returns a 3 dimensional array that holds the RGB values of each pixel at the position of the current
     * webcam picture. For example, getPicture()[1][2][3] is the pixel at (2,1) and the BLUE value.
     * [row][col][0] is alpha
     * [row][col][1] is red
     * [row][col][2] is green
     * [row][col][3] is blue
     */
    public int[][][] getPicture()
    {
        Image camera = null;
        try {
            int maxChars = 35000;
            //The image in question is 28,736 bytes, but I want to make sure it's bigger
            //for testing purposes as in my case, it's an image stream so it's unpredictable
            byte[] buffer = new byte[maxChars];
            //create the connection
            HttpURLConnection conn = (HttpURLConnection)(new URL(this.address+"/images/srpr/nav_logo13.png")).openConnection();
            conn.setUseCaches(false);
            //wrap a buffer around our input stream
            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            int bytesRead = 0;
            while ( bytesRead < maxChars && reader.ready() )
            {
                //reader.read returns an int - I'm assuming this is okay?
                buffer[bytesRead] = (byte)reader.read();
                bytesRead++;
                if ( !reader.ready() )
                {
                    //This is here to make sure the stream has time to download the next segment
                    Thread.sleep(10);
                }
            }
            reader.close();

            //Great, write out the file for viewing
            File writeOutFile = new File("testgoog.png");
            if ( writeOutFile.exists() )
            {
                writeOutFile.delete();
                writeOutFile.createNewFile();
            }
            FileOutputStream fout = new FileOutputStream(writeOutFile, false);
            //FileWriter fout = new FileWriter(writeOutFile, false);
            //needed to make sure I was actually reading 100% of the file in question
            System.out.println("Bytes read = "+bytesRead);
            //write out the byte buffer from the first byte to the end of all the chars read
            fout.write(buffer, 0, bytesRead);
            fout.flush();
            fout.close();

            //Finally use a byte stream to create an image
            ByteArrayInputStream byteImgStream = new ByteArrayInputStream(buffer);
            camera = ImageIO.read(byteImgStream);
            byteImgStream.close();
        } catch ( Exception e ) { e.printStackTrace(); }
        return ImgExample.imageToPixels(camera);
    }

    public static int[][][] imageToPixels (Image image)
    {
        //there's a bunch of code here that works in the real program, no worries
        //it creates a 3d arr that goes [x][y][alpha, r, g, b val]
        //e.g. imageToPixels(camera)[1][2][3] gives the pixel's blue value for row 1 col 2
        return new int[][][]{{{-1,-1,-1}}};
    }

    public static void main(String[] args)
    {
        ImgExample ex = new ImgExample();
        ex.getPicture();
    }
}

Answer 1

The problem as I see it is that you're using Readers. In Java, Readers are for processing character streams, not binary streams, and the character conversions that it does are most likely what's changing your bytes on you.

Instead, you should read() from the InputStream directly. InputStream's read() will block until data is available, but returns -1 when the end of the stream is reached.

Edit: You can also wrap the InputStream in a BufferedInputStream.