2D image feature extraction.

[Seeya]

Following is the program for 2d image extraction, can anybody plz explain me the first for loop??
/*
*<applet code=HistoGrab.class width=314 height=400>
*<param name=img value=input.jpg>
*</applet>*/
import java.applet.*;
import java.awt.*;
import java.awt.image.*;
public class HistoGrab extends Applet{
Dimension d;
Image img;
int iw,ih;
int pixels[];
int w,h;
int hist[]=new int[256];
int max_hist=0;

public void init()
{
d=getSize();
w=d.width;
h=d.height;

try
{
img=getImage(getDocumentBase(),getParameter("img") );
MediaTracker t=new MediaTracker(this);
t.addImage(img,0);
t.waitForID(0);
iw=img.getWidth(null);
ih=img.getHeight(null);
pixels=new int[iw*ih];
PixelGrabber pg=new PixelGrabber(img,0,0,iw,ih,pixels,0,iw);
pg.grabPixels();

}catch(InterruptedException e){};

for(int i=0;i<iw*ih;i++)
{
int p=pixels[i];
int r=0xff & (p>>16);
int g=0xff & (p>>8);
int b=0xff & (p);
int y=(int)(.33 * r +.56 * g + .11 * b);
hist[y]++;

}
for(int i=0;i<256;i++)
{
if(hist[i]>max_hist)
max_hist=hist[i];
}
}

public void update(){}

public void paint(Graphics g){

g.drawImage(img,0,0,null);
int x=(w-256)/2;
int lasty =h-h * hist[0]/max_hist;
for(int i=0;i<256;i++,x++){
int y=h-h * hist[i]/max_hist;
g.setColor(new Color(i,i,i));
g.fillRect(x,y,1,h);
g.setColor(Color.red);
g.drawLine(x-1,lasty,x,y);
lasty=y;
}
}
}

[DarrylBurke]

BB Code List - Java Programming Forum

can anybody plz explain me the first for loop?

What's there to explain? Tell us what you understand so we can take it from there.
The for Statement (The Java™ Tutorials > Learning the Java Language > Language Basics)

db

[DarrylBurke]

Isn't that code under copyright? Do you have the author's permission to reproduce it in a public forum?

db

[Seeya]

Its not that i dnt knw how for loop works, i didn't understand what " (p>>16) " mean, i mean frm where did this 16 and 8 value come frm. and also the values .33,.56 and .11.

[DarrylBurke]

Isn't that code under copyright? Do you have the author's permission to reproduce it in a public forum?

Please answer this, or this thread may be removed.

db

[DarrylBurke]

Its not that i dnt knw how for loop works, i didn't understand what " (p>>16) " mean, i mean frm where did this 16 and 8 value come frm. and also the values .33,.56 and .11.

Use proper words.

db

[Seeya]

I have no idea about that, i saw that code in reference book, i didnt know anything about the copyright issues, so to be on safer side please remove this thread.

[ronakagrawal2006]

there are 24 bits in p. each of 8 bits contain the values for red,green and blue. you are suppose to extract them.so we and them with 0000FF(1111 1111) which will set the remaining bits to 0.so for red,we are suppose to get the 1st 8 bits,so we shift the 16 bits to right.i.e if the bits are 1101 1101 1110 1110 1001 1001(before shift)it will become 0000 0000 0000 0000 1101 1101 after shift. now we and it with 0000ff so we get the 1st eight bits untouched that is the value for red.
for next step we shift by eight for green
nd in the last step we do it for blue.
Note:0x notifies a hexadecimal number.i.e 0xff = FF= 00ff=0000FF.

[Seeya]

Hey thanks a lot, got my doubts cleared !!

[ronakagrawal2006]

Hey thanks a lot, got my doubts cleared !!

anytime :)