Binarization.java

package uk.co.mmscomputing.image.operators;

import java.awt.image.*;

public class Binarization extends Operator{

  private int rshift=0,gshift=0,bshift=0;

  public Binarization(){}

  public Binarization(int threshold){
    rshift+=64-(threshold*128)/100;
    gshift+=64-(threshold*128)/100;
    bshift+=64-(threshold*128)/100;
  }

  public BufferedImage filter(BufferedImage image){
    switch(image.getType()){
    case BufferedImage.TYPE_BYTE_BINARY: return image;
    case BufferedImage.TYPE_BYTE_GRAY:   return filterGray(image);
    default:                             return filterRGB(image);
    }
  }

  public BufferedImage filterGray(BufferedImage image){
    int c;
    int w=image.getWidth();
    int h=image.getHeight();

    Histogram hs=new Histogram(256);

    for(int y=0;y<h;y++){
      for(int x=0;x<w;x++){
        c=image.getRGB(x,y)&0x000000FF;
        hs.write(c);
      }
    }
    int t=hs.getThreshold();

    System.out.println("Threshold=["+t+"]");

    BufferedImage dest=new BufferedImage(w,h,BufferedImage.TYPE_BYTE_BINARY);

    for(int y=0;y<h;y++){
      for(int x=0;x<w;x++){
        c=image.getRGB(x,y)&0x000000FF;
        if(c>t){
          dest.setRGB(x,y,-1);
        }else{
          dest.setRGB(x,y,0);
        }
      }
    }
    return dest;
  }

  public BufferedImage filterRGB(BufferedImage image){
    int c;
    int w=image.getWidth();
    int h=image.getHeight();

    Histogram rhs=new Histogram(256);
    Histogram ghs=new Histogram(256);
    Histogram bhs=new Histogram(256);

    for(int y=0;y<h;y++){
      for(int x=0;x<w;x++){
        c=image.getRGB(x,y);
        rhs.write((c>>16)&0x000000FF);
        ghs.write((c>> 8)&0x000000FF);
        bhs.write( c     &0x000000FF);
      }
    }
    int rt=rhs.getThreshold()+rshift;
    int gt=ghs.getThreshold()+gshift;
    int bt=bhs.getThreshold()+bshift;

    System.out.println("Threshold[r,g,b]=["+rt+","+gt+","+bt+"]");

    BufferedImage dest=new BufferedImage(w,h,BufferedImage.TYPE_BYTE_BINARY);

    int r,g,b;
    for(int y=0;y<h;y++){
      for(int x=0;x<w;x++){
        c=image.getRGB(x,y);
        r=(c>>16)&0x000000FF;
        g=(c>> 8)&0x000000FF;
        b= c     &0x000000FF;

        if((r>rt)||(g>gt)||(b>bt)){
          dest.setRGB(x,y,-1);
        }else{
          dest.setRGB(x,y,0);
        }
      }
    }
    return dest;
  }
}

/*
	[1] Shunji Mori; Optical Character Recognition (1999); John Wiley & Sons
    	4.2 Thresholding selection based on global discriminant analysis; pp.112

  [2] Ioannis Pavlidis, Vassilios Morellas, Pete Roeber; Programming Cameras and Pan-Tilts with DirectX and Java
      Morgan-Kaufmann Publishers; ISBN 1-55860-756-0
      pp.69

  Original Paper:

  [3] Otsu,N.A Threshold Selection Method from Gray-Level Histograms.
      IEEE Transactions on Systems,Man, and Cybernetics,1979,vol.9,pp.62-66
*/