I am suspecting that my webcam is outputting dublicate frames. So I wanted to compare the incoming frame with a stored copy of the previous frame.

However I came across a curious problem when I tried to copy the camera frame into a PImage. When I compare the brightness after having copied the new frame from the camera into my PImage. It is always off by one...

Here is my code

import processing.video.*;

Capture cam;
boolean newFrame = false;
PImage oldCam;

void setup(){
 size(320, 240);  
 cam = new Capture(this, width, height);
 oldCam = new PImage(width, height);
}

void draw(){
 if(newFrame){
   //compare brightness before copy
   println("before copy    new: " + brightness(cam.pixels[0]) + "   old: " + brightness(oldCam.pixels[0]));
   oldCam.copy(cam,0,0,width,height,0,0,width,height);
   //oldCam.loadPixels();
   //oldCam.updatePixels();
   //compare brightness after copy - it should now be the same however it is always off by one
   println("after copy    new: " + brightness(cam.pixels[0]) + "   old: " + brightness(oldCam.pixels[0]));
   newFrame = false;
 }
 
 image(cam, 0, 0);
}

void captureEvent(Capture c){
 c.read();
 newFrame = true;
}


And here is an example of my console output:
before copy    new: 63.0   old: 68.0
after copy    new: 63.0   old: 62.0
before copy    new: 63.0   old: 62.0
after copy    new: 63.0   old: 62.0
before copy    new: 58.0   old: 62.0
after copy    new: 58.0   old: 57.0

As you can see after having copied the image the brightness is always off by one - even though they should be identical. I have tried the old load and update pixels trick but no luck.

Any ideas?

/lars

oldCam = cam.get();

did the trick Thanks

Quite strange - it seems that I get quite a few dublicate frames from my webcam. Well - at least now I can detect it properly.