I'm creating a sketch to analyze realtime video and see if there has been any movement. The sketch then saves any frames which are significantly different from the frame before it.

The sketch waits for 50 frames while the camera initialises. It then duplicates the two frames it needs to compare, and starts comparing & duplicating from there on in. To compare the sketch creates a pixel grid (using the gridVertStep/gridHorzStep variables) and compares colour difference, on these pixel, between the current and previous frames.

This all works well, but runs relatively slowly, I'm on a Dual 1.42Ghz G4 mac, not the fastest machine I'd admit, but even running this at 320x240 the average framerate is about 8fps. not exactly inspiring.

Any ideas on how I can speed this up?

Cheers
Niall


//INIT//
// procesing libraries
import processing.video.*;
import processing.opengl.*;

// variables + setup
Capture myCapture;
int myFrameRate = 25;
boolean initialPlay = true;
PImage frameA;
PImage frameB;

// grid setup
int gridVertStep = 32;
int gridHorzStep = 24;
int gridVert = 1;
int gridHorz = 1;
int gridLookUp = gridVert + gridHorz;

//difference detect
float gridCount = 0;
float gridVariance = 30;
float varianceCount = 0;
float percentage;

//saving bits
int thisFrameCount = 0;
String name;


//SETUP//
void setup () {
 size(320,240);
 background(128);
 this.framerate(myFrameRate);
 String s = "IIDC FireWire Video";
 myCapture = new Capture(this, s, width, height, 25);
}

//LOOP//
void draw () {
 if (frameCount == 50) {
   myCapture.read();
   image (myCapture, 0, 0);
   initDuplicate();
 }
 else if (frameCount > 50) {
   detectChange1();
   percentage = (100 * (varianceCount/gridCount));
   println("percentage: " + percentage);
   if (percentage > 25) {
     saveImage();
   }
   varianceCount = 0;
   myCapture.read();
   image (myCapture, 0, 0);
   duplicate();

 }
 else {
   myCapture.read();
   image (myCapture, 0, 0);
 }
 println("framerate: " + framerate);
}


//FUNCTIONS//
void initDuplicate() {
 frameA = get();
 frameB = get();
}

void detectChange1() { // dotGrid
 //create grid
 gridCount = 0;
 for (gridVert = 0; gridVert < myCapture.height; gridVert += gridVertStep) {
   for (gridHorz = 0; gridHorz < myCapture.width; gridHorz += gridHorzStep) {
     gridCount ++;
     // get colour of grid then check to see if its different
     gridLookUp = gridHorz+gridVert;
     color c = frameA.pixels[gridLookUp];
     color d = frameB.pixels[gridLookUp];

     if ((red(c)+green(c)+green(c)) - (red(d)+green(d)+green(d)) > gridVariance || (red(c)+green(c)+green(c)) - (red(d)+green(d)+green(d)) < -1 * gridVariance) {
       varianceCount ++;
     }  
   }
 }
}

void duplicate() {
 frameA = frameB.get();
 frameB = get();
}

void saveImage() {
 if (thisFrameCount < 10) {
   name = "image-000" + thisFrameCount + ".tga";
 }
 else if (thisFrameCount < 100) {
   name = "image-00" + thisFrameCount + ".tga";
 }
 else if (thisFrameCount < 1000) {
   name = "image-0" + thisFrameCount + ".tga";
 }
 save(name);
 thisFrameCount += 1;
}