Processing 1.0 - Processing Discourse - capture images and then sequence them?

intellijel

capture images and then sequence them?
Jul 22^nd, 2009, 8:51pm

I want to use a camera (for now it can just be my webcam) to capture a fixed amount (e.g 16) still images at triggered events (e.g. mouse clicks).

Then I want to display those images in the sequence they were captured at a set interval.

Any tips people would have for implementing this?

My first instinct is to use the Video library to capture the video stream and then use save(filename-####.jpg) to save specific frames.

What would be the best way to stop the video capture and then load and display the images?

naus3a

Re: capture images and then sequence them?
Reply #1 - Jul 23^rd, 2009, 3:34am

i'll make an example using opencv; you can do the same with any video lirary simply changing the opencv calls with you chosen library calls.
to capture at mouse click use something like:

Code:


PImage[] captured_frames;
...
int cnt = 0;
...
void mousePressed(){
   captured_frames[cnt] = opencv.image();
   cnt++;
}

to playback, use something like:
Code:


...
int cnt2 = 0;
...
void draw(){
...
   my_playback();
...
}
...
void my_playback(){
   image(captured_frames[cnt2],0,0);
   cnt2++;
}

intellijel

Re: capture images and then sequence them?
Reply #2 - Jul 23^rd, 2009, 8:19am

thanks for the info!

I tried the code but I have an error "exception in animation thread" whenever I try to save the frame:

Code:

import hypermedia.video.*;

PImage[] captured_frames;
OpenCV opencv;

int cnt = 0;
boolean playmode = false;
 

void setup() {
   size( 320, 240 );
    opencv = new OpenCV( this );
    opencv.capture( width, height );  // open video stream


}

void draw(){
if (playmode) {
   my_playback();
} else {
opencv.read(); 
image( opencv.image(), 0, 0 );
  }
}


void my_playback(){
   for (int i = 0; i<cnt; i++) {
   image(captured_frames[i],0,0);
    delay(200);
   }
  
}

void keyPressed() {
  if (key == 'z') {
     captured_frames[cnt] = opencv.image();
     cnt++;
     println("Z key pressed");
  } else if (key == 'x'){
    playmode = true;
  }
}

any idea what's wrong?

PhiLho

Re: capture images and then sequence them?
Reply #3 - Jul 23^rd, 2009, 9:56am

intellijel wrote on Jul 23^rd, 2009, 8:19am:

I have an error "exception in animation thread"
[...]
any idea what's wrong

Reporting at least the first few lines of an exception always helps in pinning down "what's wrong"...

Now, looking harder at your code, I can guess the exception is on captured_frames array which seems never initialized.

intellijel

Re: capture images and then sequence them?
Reply #4 - Jul 23^rd, 2009, 10:05am

PhiLho wrote on Jul 23^rd, 2009, 9:56am:

intellijel wrote on Jul 23^rd, 2009, 8:19am:

I have an error "exception in animation thread"
[...]
any idea what's wrong

Reporting at least the first few lines of an exception always helps in pinning down "what's wrong"...

Now, looking harder at your code, I can guess the exception is on captured_frames array which seems never initialized.

here's the full error:

Code:

Exception in thread "Animation Thread" java.lang.NullPointerException
	at sketch_jul23a.mousePressed(sketch_jul23a.java:65)
	at processing.core.PApplet.handleMouseEvent(PApplet.java:1608)
	at processing.core.PApplet.dequeueMouseEvents(PApplet.java:1545)
	at processing.core.PApplet.handleDraw(PApplet.java:1437)
	at processing.core.PApplet.run(PApplet.java:1328)
	at java.lang.Thread.run(Thread.java:613)

intellijel

Re: capture images and then sequence them?
Reply #5 - Jul 23^rd, 2009, 10:13am

ok that was a dumb mistake (not initializing the array)

but I now have a different problem where it will only playback a single image and stop.

When I click 'x' it just shows me the last image saved, not a sequence of the last five.

here is the corrected code:

Code:

import hypermedia.video.*;

int maxFrames = 255;

PImage[] captured_frames= new PImage[maxFrames] ;
OpenCV opencv;

int cnt = 0;
boolean playmode = false;
 

void setup() {
   size( 320, 240 );
    opencv = new OpenCV( this );
    opencv.capture( width, height );  // open video stream


}

void draw(){
if (playmode) {
   my_playback();
} else {
opencv.read(); 
image( opencv.image(), 0, 0 );
  }
}


void my_playback(){
   for (int i = 0; i<cnt; i++) {
   image(captured_frames[i],0,0);
    delay(200);
   }
  
}

void keyPressed() {
  if (key == 'z') {
     captured_frames[cnt] = opencv.image();
     cnt = (cnt+1)%maxFrames;
     println("Z key pressed");
  } else if (key == 'x'){
    playmode = true;
  }
}

PhiLho

Re: capture images and then sequence them?
Reply #6 - Jul 23^rd, 2009, 10:26am

That's the classical problem of animations in Processing: we all try (in our early days of Processing) to draw several things in draw(), adding delay() to ensure proper rate. But it just doesn't work: screen is updated only at the end of draw().
You have to add a logic to draw an image, count a number of frames, draw next image, etc.

intellijel

Re: capture images and then sequence them?
Reply #7 - Jul 23^rd, 2009, 4:32pm

PhiLho wrote on Jul 23^rd, 2009, 10:26am:

That's the classical problem of animations in Processing: we all try (in our early days of Processing) to draw several things in draw(), adding delay() to ensure proper rate. But it just doesn't work: screen is updated only at the end of draw().
You have to add a logic to draw an image, count a number of frames, draw next image, etc.

awesome, this was the approach I needed to know about!