Image Slicer ..

Question

Hey there,
I have been writing this program to slice an image into smaller parts. Quite simple, you give it an image, an array of rows and an array of columns and it gives you the image sliced up. (code follows)
All is well and good when I provide it with a PNG but with other formats i'm getting some strange results.
n.b this isnt too urgent as i shall probably only be wanting to slice PNG files; but it would be nice to know i could do others if i should want to, and anyway, i would really like to know why it shouldnt work.
Attempting it with a GIF appears to work, but when I try to view the new files I am told they cannot be shown as they contain errors.
JPGs give me a run time error, as the ImageTypeSpecifier returned by the call to ImageReader.getRawImageType(0) is null.
Anyway, heres the code,
import java.awt.*;
import java.awt.image.*;
import javax.imageio.*;
import javax.imageio.stream.*;
import java.io.*;
public class ImageSlicer {
     public static void main(String args[]) throws IOException {
          ImageSlicer is = new ImageSlicer("unchopped.png");
          int[] r = {20,50};
          int[] c = {40,250};
          is.setRows(r); is.setCols(c);
          is.slice();
     public ImageSlicer(String image_file) {
          img_f = image_file;
          img = Toolkit.getDefaultToolkit().createImage(img_f);
          mt = new MediaTracker(new Container());
          mt.addImage(img,0);
          try {
              mt.waitForID(0);
          } catch(InterruptedException e){}
     private String img_f;
     private Image img;
     private int[] rows, cols;
     private MediaTracker mt;
     public void setRows(int[] row_cut) {
          rows = new int[row_cut.length+1];
          int i;
          for(i=0;i<row_cut.length;i++)
               rows[i] = row_cut;
          rows[i] = img.getHeight(null);
     public void setCols(int[] col_cut) {
          cols = new int[col_cut.length+1];
          int i;
          for(i=0;i<col_cut.length;i++)
               cols[i] = col_cut[i];
          cols[i] = img.getWidth(null);
     public void slice() throws IOException {
          long strt = System.currentTimeMillis();
          if(rows==null) {
               rows = new int[1];     rows[0] = img.getHeight(null);
          if(cols==null) {
               cols = new int[1];     cols[0] = img.getWidth(null);
          ImageInputStream iis = ImageIO.createImageInputStream( new File(img_f) );
          ImageReader ir = (ImageReader)ImageIO.getImageReaders(iis).next();
          ir.setInput(iis);
          int i,j,x,y,w,h; BufferedImage b;
          for(i=0;i<rows.length;i++)
               for(j=0;j<cols.length;j++) {
                    if(i==0)
                         y = 0;
                    else
                         y = rows[i-1];
                    if(j==0)
                         x = 0;
                    else
                         x = cols[j-1];
                    w = cols[j] - x;
                    h = rows[i] - y;
                    b = makeSlice(x,y,w,h,ir.getRawImageType(0));
                    String f = img_f.substring(0,img_f.lastIndexOf(".")) + "_" + i + "_" + j + "." + ir.getFormatName();
                    ImageIO.write(b,ir.getFormatName(),new File(f));
          long time = System.currentTimeMillis()-strt;
          System.err.println("image sliced in " + time + "ms.");
     public BufferedImage makeSlice(int x, int y, int w, int h, ImageTypeSpecifier its) {
          BufferedImage bi = its.createBufferedImage(w,h);
          Image i = Toolkit.getDefaultToolkit().createImage(
                    new FilteredImageSource(img.getSource(),new CropImageFilter(x,y,w,h)) );
          mt.addImage(i,1);
          try {
          mt.waitForID(1);
          } catch(InterruptedException e){}
          Graphics g = bi.createGraphics();
          g.drawImage(i,0,0,null);
          g.dispose();
          return bi;

Answer 1

I love a nice challenge to get the brain thinking. This one was fun.
Heres what I came up with (not really sure what exactly you were trying to do with your rows and columns....)
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.awt.image.Raster;
import java.io.File;
import javax.imageio.ImageIO;
* @author Ian Schneider
public class ImageSlicer {
    public static final void main(String[] args) throws Exception {
        String srcFile = args[0];
        String[] names = args[0].split("\\.");
        int w = Integer.parseInt(args[1]);
        int h = Integer.parseInt(args[2]);
        BufferedImage img = ImageIO.read(new File(srcFile));
        slice(img,w,h,names[0],names[1]);
    static void slice(BufferedImage img,int w,int h,String name,String ext) throws Exception {
        BufferedImage piece = new BufferedImage(w,h,img.getType());
        int iw = img.getWidth();
        int ih = img.getHeight();
        Rectangle srcRect = new Rectangle(w,h);
        int idx = 0;
        for (int x = 0; x < iw; x+=w) {
            for (int y = 0; y < ih; y+=h) {
                srcRect.setLocation(x,y);
                Raster rect = img.getData(srcRect);
                piece.getRaster().setRect(-x,-y,rect);
                File f = new File(name + "_" + idx++ + "." + ext);
                System.out.println("writing " + f);
                ImageIO.write(piece,ext,f);
}Couple of things to note here:
1) reusing the BufferedImage destination piece. This will make things much more efficient for a large image.
2) creating the BufferedImage using the same type as the source image (no more messed up output)
3) using Raster to copy the data - makes things easier. Note the -x,-y translation in the setRect method. This is because the getData method returns a Raster "view" not a copy of the data. The x and y locations are therefore the same and must be translated back to 0,0 for the copy.
4) the input arguments are file and desired size of resulting pieces (width X height)
There are obviously lots of improvements to make here, I tried to focus on just the image processing portion.
Have fun