Displaying Multiple Images With a Loop

I'm trying to display an image from a camera feed each time through the loop, but right now it only displays a blank figure each time through and then only displays the image once the loop terminates.

while 1
    frame = getsnapshot(vid);

      newFaceList = faceRecog(frame, kernel, prevFaceList);

      for i = 1:size(newFaceList)
         face = newFaceList(i);
         rowshift = uint32( face.pos(1) - (face.face_size(1)) );    
         colshift = uint32( face.pos(2) - (face.face_size(2)) );     
         if face.type == 2
             zombieResize = imresize(zombieFace, [face.face_size(1) face.face_size(2)]);
             zsize = size( zombieResize );
             frame( uint32(1:zsize(1) )+rowshift, uint32(1:zsize(2) )+colshift, :) = zombieResize;
         elseif face.type == 1
             humanResize = imresize(humanFace, [face.face_size(1) face.face_size(2)]);
             frame((1:size(zombieResize,1))+rowshift, (1:size(zombieResize,2))+colshift, :) = humanResize;
         end
      end

      imshow(frame)

      prevFaceList = newFaceList;
  end

How can I get the program to display the most recent image for each iteration?

Answer 1

[Jan]

Does inserting a drawnow after imshow help?

[Michael Plante]

It does make the images appear with each iteration, but it does seem to slow down the program significantly. I'd like to avoid that if at all possible.

[Matt Kindig]

One way that might speed up the program is to only modify the 'CData' (the actual image content) each time, rather than calling imshow (which actually creates a new image object). Outside your while loop, call imshow with the first frame data, and save the handle. Then instead of the imshow() call, just set the 'CData' property for that handle. Something like this:

himg = imshow( first_frame);
while 1,
    frame =  getsnapshot(vid);
    %all your other code here
    set(himg, 'CData', himg);  %instead of imshow
    drawnow;
    prevFaceList = newFaceList;
end

Again, I'm not sure what kind of speed benefits you get, but might be worth a shot.

Answer 2

[Image Analyst]

Can the camera go live? If so, why don't you just use the preview() function?

[Michael Plante]

There was more code between getting the snapshot and displaying it concerning facial recognition and overlaying other image data depending on the results of the facial recognition, so I need individual frames instead of just a video feed. I'll edit the question and include that part.

[Image Analyst]

What's the class of humanface and humanresize? Is it single or double? If so, try

cla; % Prevent stuffing too many images into the axes.
imshow(frame, []);
drawnow;
pause(0.5); % Pause for 1/2 second before next frame blows it away.

to scale it properly for display.