The Distance Transform of a Binary Image

[nithyasubramanian]

Description : This is a image processing program which performs the distance transform of a binary image.Distance transform is widely used for image thinning and finding skeleton of an image.

//1:newfndistrans.java
//2:A bmp monochrome image(preferably 512-512)
//make the image from mspaint or any other source



import java.io.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class newfndistrans extends JFrame{
frame frm=null;
File f;
FileInputStream ff;
Color cl;
int count;
int a[];

int rnum,gnum;
int xsize;
int ysize;
final int sample=5;
String str=null;

newfndistrans(String str)
{
super(str);
frm=new frame();


count=0;
a=new int[8];
rnum=0;gnum=0;
}

public void paint(Graphics g)
{
int x,y,i=0,j=0,temp;

try{

System.out.println("Starting");
System.out.println("filename="+frm.getfilename());
try{f=frm.getfilename();
ff=new FileInputStream(f);
}catch(Exception e){
System.out.println("error in reading file");
}
ff.skip(18);
i=ff.read();
i=((ff.read()<<|i);
i=((ff.read()<<16)|i);
i=((ff.read()<<24)|i);
xsize=i;
System.out.println("width="+xsize);
i=0;
i=ff.read();
i=((ff.read()<<|i);
i=((ff.read()<<16)|i);
i=((ff.read()<<24)|i);
ysize=i;
System.out.println("Height="+ysize);

ff.skip(38);//62-(2+16+4+4=26)=36, actually total=62 Bytes header
//note:make it 38 for nrectbit1.bmp and nrectbit2.bmp
x=0;y=ysize;
int pix[][],mat1[][];
pix=new int[xsize][ysize];
mat1=new int[xsize][ysize];
System.out.println("here");
while(true)
{

rnum=ff.read();
//System.out.println("rnum="+rnum);
if(rnum==-1)break;
count=7;
//image has 0 for black ,1 for white,but my convention is opposite
while(rnum>0)
{
gnum=rnum%2;
if(gnum==0)a[count]=1;
else a[count]=0;
count--;
rnum=rnum/2;
}
while(count>=0)
{a[count]=1;count--;
}
for(i=0;i<=7;i++)
{if(a==0)cl=new Color(255,255,255);
else cl=new Color(0,0,0);
pix

• [y-1]=a;
  mat1
  • [y-1]=a;
    g.setColor(cl);
    g.drawRect(x,y,1,1);
    x++;
    if(x==xsize){x=0;y--;}
    }
    }//end while
    
    System.out.println("File read successfully");
    //sleep for 4 seconds(4000 msec)
    try{Thread.sleep(4000);
    }catch(Exception e){}
    //clear the region where the image was drawn,area near the boundaries
    are
    also cleaned
    for(j=0;j<=ysize+2;j++)
    for(i=0;i<=xsize+2;i++)
    g.clearRect(i,j,1,1);
    //cleaning done above
    
    //0 means white,1 means black
    //perform the distance transform
    for(j=0;j<ysize;j++)
    for(i=0;i<xsize;i++)
    {
    if(mat1[j]==0)continue;
    if((j==0)||(j==ysize-1)){mat1[j]=1;continue;}
    if((i==0)||(i==xsize-1)){mat1[j]=1;continue;}
    
    
    temp=findmin(mat1[i-1][j],mat1[i-1][j-1],mat1[j-1],mat1[i+1][j-1]);
    mat1[j]=temp+1;
    }
    
    
    
    //perform the distance transform from bottom
    for(j=ysize-1;j>=0;j--)
    for(i=xsize-1;i>=0;i--)
    {if(mat1[j]==0)continue;
    if((j==0)||(j==ysize-1)){mat1[j]=1;continue;}
    if((i==0)||(i==xsize-1)){mat1[j]=1;continue;}
    
    
    temp=findmin(mat1[i-1][j+1],mat1[j+1],mat1[i+1][j+1],mat1[i+1][j]);
    if(temp>(mat1[j]-1))temp=mat1[j]-1;
    mat1[j]=temp+1;
    }
    
    int max=-9999,colornum,i1,j1,globmax=-9999;
    x=0;y=0;
    for(j=0;j<ysize-(ysize%sample);j+=sample)
    for(i=0;i<xsize-(xsize%sample);i+=sample)
    {
    max=-9999;
    for(j1=j;j1<j+sample;j1++)
    for(i1=i;i1<i+sample;i1++)
    if(max<mat1[i1][j1])
    {
    max=mat1[i1][j1];
    //xcord=i1;ycord=j1;
    }
    //out of both above for loops
    if(globmax<max)globmax=max;
    
    
    if(max!=0)
    {
    System.out.println("max="+max);
    for(j1=j;j1<j+sample;j1++)
    for(i1=i;i1<i+sample;i1++)
    mat1[i1][j1]=max;
    }
    
    }
    System.out.println("globmax="+globmax);
    for(j=0;j<ysize;j++)
    for(i=0;i<xsize;i++)
    {colornum=(mat1[j]*255)/globmax;//contrast enhancement
    colornum=255-colornum;
    cl=new Color(colornum,colornum,colornum);
    g.setColor(cl);
    g.drawRect(i,j,1,1);
    }
    ff.close();
    System.out.println("program ends");
    }//end try block
    catch(Exception e)
    {System.out.println("Error"+e.getMessage());
    }
    
    
    
    }
    int findmin(int num1,int num2,int num3,int num4)
    {
    int min=4000;
    if(min>num1)min=num1;
    if(min>num2)min=num2;
    if(min>num3)min=num3;
    if(min>num4)min=num4;
    return(min);
    }
    
    public static void main(String args[])
    {
    
    JFrame frm=new newfndistrans("Distance Transform");
    frm.setSize(700,700);
    frm.setVisible(true);
    
    
    }//end main()
    
    }// end class fndistrans
    class frame extends JFrame{
    JButton but;
    JFileChooser fch;
    String filename;
    File file=null;
    //Container con;
    boolean temp;
    frame()
    { super("FileReading");
    setSize(700,500);
    setLayout(new FlowLayout());
    
    temp=true;
    but=new JButton("Open the binary file");
    add(but);
    fch=new JFileChooser();
    but.addMouseListener(new MouseAdapter()
    { public void mousePressed(MouseEvent me)
    {
    int retval=fch.showOpenDialog(but);
    if(retval==JFileChooser.APPROVE_OPTION)
    {
    file=fch.getSelectedFile();
    filename=file.getName();
    System.out.println("1filename="+filename);
    temp=false;
    }
    
    }
    
    });
    setVisible(true);
    while(temp);
    }//end constructor
    File getfilename()
    {System.out.println("filename="+filename);
    return file;
    }