Processing 1.0 - Processing Discourse - Calculating difference of two images

seltar

Calculating difference of two images
May 27^th, 2005, 1:33am

Here's a little function i mashed up..
It calculates the difference between two images, as the topic says. It is fairly simple though, and i would like any comments on to how i possibly could improve any of it.

i use it to record changes to a previously taken videosnapshot.

color [] a, is videoinput.pixels, and color [] b is the image you are checking up against.
tip: if you use a singlecolored source-image, it excludes that color from the video-input.

usage in draw():
image(renderDifference(cam.pixels,img.pixels,10),0,0);

Code:

 
PGraphics3 renderDifference(color [] a, color [] b, float sens)
{
  PGraphics3 tmp = new PGraphics3(width,height,null);
  color trans = color(0,255,0); // the color of the pixels that haven't changed
  for(int i = 0; i < width; i++)
  {
    for(int j = 0; j < height; j++)
    {
	float rA = red(a[j*width+i]);
	float gA = green(a[j*width+i]);
	float bA = blue(a[j*width+i]);
	float rB = red(b[j*width+i]);
	float gB = green(b[j*width+i]);
	float bB = blue(b[j*width+i]);
	boolean changed = false;
	
	// RED
	if((rA>(rB+sens)) || ((rA+sens)<rB)) changed = true;
	
	// GREEN
	if((gA>(gB+sens)) || ((gA+sens)<gB)) changed = true;

	// BLUE
	if((bA>(bB+sens)) || ((bA+sens)<bB)) changed = true;
	
	if(changed)
	  tmp.pixels[j*width+i] = a[j*width+i];
	else
	  tmp.pixels[j*width+i] = trans;
    }
  }
  return tmp;
}

void mousePressed()
{
  color c = Scamera.pixels[mouseY*width+mouseX]; 
  // get the current color under mouse
  // for setting single-colored source images
  // # add some function to color source image
}

-seltar

« Last Edit: May 27^th, 2005, 2:43am by seltar »

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large-x YaBB Newbies Offline Posts: 4	Re: Calculating difference of two images Reply #1 - May 27^th, 2005, 1:06pm you might try using HSB colorspace instead of RGB; you would only need to test one value, hue or brightness, instead of 3

st33d

Re: Calculating difference of two images
Reply #2 - May 29^th, 2005, 2:00am

A speedier method would be trim those floats to ints using a trick I learned from the seniors:
Code:


for (int iy = 0; iy < img1.height; iy++){
for (int ix = 0; ix < img1.width; ix++){
color c1 = img1.pixels[ix + iy * img1.width];
color c2 = img2.pixels[ix + iy * img2.width];
int  r1=c1>>16&0xff;
int  g1=c1>>8&0xff;
int  b1=c1&0xff;
int  r2=c2>>16&0xff;
int  g2=c2>>8&0xff;
int  b2=c2&0xff;
display.pixels[ix + iy * display.width] = color (abs(r1-r2),abs(g1-g2),abs(b1-b2));
}
}

And I got a nice brightness value reader off of Fry:
Code:


int gray(color p) {
  return max((p >> 16) & 0xff, (p >> 8) & 0xff, p & 0xff);
}

Handy stuff I'm still using.

Quasimondo

Re: Calculating difference of two images
Reply #3 - May 31^st, 2005, 10:13am

As the size of the camera image is usually the same size as the canvas, there is a lot of optimizations you can apply - get rid of all those multiplications in the first place.

The second, much bigger optimization is to use bitwise XOR (^) instead of abs(a-b) - it also makes the extraction of the rgb values obsolete:

Code:


function dif(int[] img){
   for (int i=pixels.length;--i>-1;pixels[i]^=img[i]){}
}

function imgDif(int[] img1,int[] img2){
   for (int i=pixels.length;--i>-1;pixels[i]=img1[i]^img2[i]){}
}

Mario Klingemann | Quasimondo | Incubator | côdeazur

cosmin Full Member Offline Posts: 103	Re: Calculating difference of two images Reply #4 - May 31^st, 2005, 10:44am and maybe if((rA>(rB+sens)) \|\| ((rA+sens)<rB)) changed = true; should be if (sens > abs(rA-rB)) changed = true; seems cleaner and probably a little faster
	http://10megatons.com

cosmin

Re: Calculating difference of two images
Reply #5 - May 31^st, 2005, 10:59am

BTW, I'm new to this, and new to java for that matter, so I don't get this PGraphics stuff. From what I could find I understand it's better engine then the normal loadpixels / pixels because it deals with a buffer, or something like that, but I'm lacking in syntax.

So, could you post a little more code (or all of it ? Cheesy

) because I don't understand where should I get color[]b from. I tried initialising it to a white image, but that just turned the screen green, allthough color[]a is the camera image.

And I think there should be a color[]b =color[]a at the end somewhere, but that's another thing.

And I'd really like to see this thing, because I built my own camera difference thingie and it's a little slow, so if I'm gaining performance, I want in

Code:


import processing.video.*;
Capture cam;
PImage img;

color c;
int camW = 320;
int camH = 240;

void setup(){
  size(camW,camH);
  fill(255,0,0);
  String s =  Capture.list()[0];
  cam = new Capture(this, s, camW,camH);
  img = new PImage(width,height);
  for (int i=0;i<width*height; i++){
    img.pixels[i] = color(0,0,0);
  }
}



void draw(){
   image(renderDifference(cam.pixels,img.pixels,10),0,0);
 }

That's it, and the other file is your renderDifference function

http://10megatons.com

seltar

Re: Calculating difference of two images
Reply #6 - May 31^st, 2005, 2:54pm

check out http://seltar.wliia.org .. rewritten the webcam functions to image so they'll work on web.. with sources.. color [] b is just an image.pixels ..
the way i use it is..
color [] a = myCamera.pixels
color [] b = mySourceImage.pixels
and it calculates the difference between the two..
so it sortof looks like a greenscreen.. i've added a color [] c, for video-background.. but that's another thing..

hope you figure out what you need..if not, please post again.. i'll be glad to help you out

-seltar

I'm bored, therefore I program
http://seltar.org > seltar's special place
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http://libraries.seltar.org > seltar's libraries

cosmin Full Member Offline Posts: 103	Re: Calculating difference of two images Reply #7 - May 31^st, 2005, 4:21pm Thenk you sir, it worked. Now the cam is visible under the top image's mask. Now I gotta explre more to see what this PGraphics3 is all about.
	http://10megatons.com

cosmin

Re: Calculating difference of two images
Reply #8 - Jun 2^nd, 2005, 7:02pm

The next step. I have this code:

Code:


import processing.video.*; 
PImage img, oldCam;
Capture cam;

boolean src = false, shiftdown = false;
int sens = 70;
int[] ax,ay;
int num = 0;

void setup(){
  size(320, 240, P3D);
  framerate(20);
  String s =  Capture.list()[0];
  cam = new Capture(this, s, 320, 240, 30);

  img = loadImage("a.jpg");
  oldCam = img;
}

void draw(){
  image(renderDifference(cam.pixels, oldCam.pixels, sens),0,0);
} 



void captureEvent(Capture camera) { 
  cam.read(); 
} 





PGraphics3 renderDifference(color[] a, color[] b, int sens){
  PGraphics3 tmp = new PGraphics3(width,height,null);
  color trans = color(255,255,255); //the colour of the pixels w/ movement
  color ch = color(0,0,0); //the colour of the pixels that haven't changed
  
  for(int i = 0; i < width; i++) {
    for(int j = 0; j < height; j++){
	float bA = brightness(a[j*width+i]);
	float bB = brightness(b[j*width+i]);

	if (sens<abs(bA-bB))  tmp.pixels[j*width+i] = ch;
	else   tmp.pixels[j*width+i] = trans;
    }
  }

  for (int i=0;i<width*height;i++)  oldCam.pixels[i] = cam.pixels[i];
  return tmp;
}

The problem with it is that it flickers, it looks like a 1/1 flicker (one frame's ok, the other one is missing or something) and I'm not sure if it's from the code or not.
My camera seems pretty noisy, maybe that's it ...
OR, it just looks like flicker because it happends fast, I don't know, can't tell. Does it flicker for you too ?

If it's from the code guess I could implement something like a blending, although for what I want I don't think it's needed ... I'll have to think about that later.

And what's with those lines ... any idea ?

http://10megatons.com

seltar

Re: Calculating difference of two images
Reply #9 - Jun 2^nd, 2005, 7:17pm

well, those lines are probably linked to what the a.jpg contains i guess..

this stopped the flickering for me:
(i used new PImage instead of loading an image..)
Code:



  img = new PImage(width,height);
  oldCam = img;
}

void draw(){
  image(renderDifference(cam.pixels, oldCam.pixels, sens),0,0);
}  

void captureEvent(Capture cam) {  
  cam.read();  
}  

PGraphics3 renderDifference(color[] a, color[] b, int sens){
  PGraphics3 tmp = new PGraphics3(width,height,null);
  color trans = color(255,255,255); //the colour of the pixels w/ movement
  color ch = color(0,0,0); //the colour of the pixels that haven't changed

  for(int i = 0; i < width; i++) {
    for(int j = 0; j < height; j++){
	float bA = brightness(a[j*width+i]);
	float bB = brightness(b[j*width+i]);

	if (sens<abs(bA-bB))  tmp.pixels[j*width+i] = ch;
	else   tmp.pixels[j*width+i] = trans;
	oldCam.pixels[i] = cam.pixels[i];
    }
  }
  return tmp;
}

I'm bored, therefore I program
http://seltar.org > seltar's special place
http://snippet.seltar.org > seltar's snippet palace
http://libraries.seltar.org > seltar's libraries

st33d God Member Offline Posts: 666	Re: Calculating difference of two images Reply #10 - Jun 3^rd, 2005, 10:33pm Quasimondo wrote on May 31^st, 2005, 10:13am: The second, much bigger optimization is to use bitwise XOR (^) instead of abs(a-b) - it also makes the extraction of the rgb values obsolete Damn that's tasty. I'm still trying to comprehend bitwisdom. You learn something new everyday.