Why does not line appear over plot

I am trying to draw a skeleton over an RGB image. pos2D is a cell which holds the x,y coordinates of the body.

for w= 1:10
    color = imresize(Foto(:,:,w),COL_SCALE);
    c.im = imshow(color,[]);
    %set(c.im,'CData',color); 

      skeleton = pos2D{1,w};   
      for m = 1:19
          X1 = [skeleton(SkeletonConnectionMap(m,1),1) skeleton(SkeletonConnectionMap(m,2),1)];
          Y1 = [skeleton(SkeletonConnectionMap(m,1),2) skeleton(SkeletonConnectionMap(m,2),2)];
          line(X1,Y1, 'LineWidth', 1.5, 'LineStyle', '-', 'Marker', '+', 'Color', 'r');    
      end
  end

Outside the loop it works perfecty, i.e. if i change the w index by hand and do step by step, the line appears. However, when I do these nested loops it does not work. It only appears in the last frame before closing the loop. I tried hold on and off several times. What am I missing?

Thanks!

Answer 1

[OCDER]

Using imshow will replace the current axes and everything drawn on that axes, including the lines. To fix, use imshow once and then change CData of that image handle. This way, your lines are not deleted.

for w = 1:10
    color = imresize(Foto(:,:,w),COL_SCALE);
    skeleton = pos2D{1,w};
    if w == 1
        c.im = imshow(color, []);
    else
        c.im.CData = color;
    end
    for m = 1:19
        X1 = [skeleton(SkeletonConnectionMap(m,1),1) skeleton(SkeletonConnectionMap(m,2),1)];
        Y1 = [skeleton(SkeletonConnectionMap(m,1),2) skeleton(SkeletonConnectionMap(m,2),2)];
        line(X1,Y1, 'LineWidth', 1.5, 'LineStyle', '-', 'Marker', '+', 'Color', 'r');    
    end
end

[Walter Roberson]

And add drawnow() after the line() call to cause them to show up immediately.

[Walter Roberson]

for w = 1:10
    color = imresize(Foto(:,:,w),COL_SCALE);
    skeleton = pos2D{1,w};
    if w == 1
        c.im = imshow(color, []);
        c.lh = line(nan, nan, 'LineWidth', 1.5, 'LineStyle', '-', 'Marker', '+' 'Color', 'r');
    else
        c.im.CData = color;
    end
    for m = 1:19
        X1 = [skeleton(SkeletonConnectionMap(m,1),1) skeleton(SkeletonConnectionMap(m,2),1)];
        Y1 = [skeleton(SkeletonConnectionMap(m,1),2) skeleton(SkeletonConnectionMap(m,2),2)];
        set(c.lh, 'XData', X1, 'YData', Y1);
        drawnow()   
    end
end

[OCDER]

Hi Andrés, Walter answered your next question. What you want to do is the first loop w = 1, do imshow and draw your 19 lines. In all other loop w > 1, adjust the data in imshow and line.

for w = 1:10
    color = imresize(Foto(:,:,w),COL_SCALE);
    skeleton = pos2D{1,w};
    if w == 1 %First time, make image and 19 lines
        c.im = imshow(color, []);
        for m = 1:19
            X1 = [skeleton(SkeletonConnectionMap(m,1),1) skeleton(SkeletonConnectionMap(m,2),1)];
            Y1 = [skeleton(SkeletonConnectionMap(m,1),2) skeleton(SkeletonConnectionMap(m,2),2)];
            c.lh(m) = line(X1, Y1, 'LineWidth', 1.5, 'LineStyle', '-', 'Marker', '+', 'Color', 'r');
        end 
    else %All other times, adjust image and 19 lines position
        c.im.CData = color;
        for m = 1:19
            X1 = [skeleton(SkeletonConnectionMap(m,1),1) skeleton(SkeletonConnectionMap(m,2),1)];
            Y1 = [skeleton(SkeletonConnectionMap(m,1),2) skeleton(SkeletonConnectionMap(m,2),2)];
            set(c.lh(m), 'XData', X1, 'YData', Y1);
            drawnow()   
        end
    end
end

Answer 2

[Andrés Méndez]

Donald,

There seems to be something about timing. If I do the CData, i just get a final black background with all the skeleton on top, no video with RGB sequence...

Things change if i put a pause(0.01) in the loop Then I see the image sequence with the skeleton drawn on top (why is this?)...however, the skeleton appears and disappears with the imshow...if I do what you suggest (c.im.CData) i can see the image sequence but the skeleton do not disappear and add one on top of each other. how do i erase the skeleton to update it with the next?

Thanks!