program for tracking the moving object in an video,by centroid method

I have made the program for tracking the moving object in an video,by centroid method, but after 44 frames an error is coming. I have located plus sign on the centroid, and it is appearing till frame 44 but after it an error is coming. Following is the error Subscript indices must be logical or real positive integers error in im(p,y) Following is my code

clc;
close all;
          %read the first frame of video
vidObj=VideoReader('tank_human.avi');
% Create an axes
      currAxes = axes;
% Read video frames until available
k=1;
    while hasFrame(vidObj)&&(k<=100)
          vidFrame = readFrame(vidObj);
          image(vidFrame, 'Parent', currAxes);
          currAxes.Visible = 'off';
          pause(1/vidObj.FrameRate);            
     F=getframe;
      %figure(2);
      %imshow(F.cdata);
      [F,map]=frame2im(F);
 im=rgb2gray(F);
 %figure(3);
%imshow(im);
im=double(im);
[row1,col1]=size(im);
if(k>18&&k<24)
  n1=120;
else if(k>=24)
  n1=140;
   else
      n1=115;
  end
end

if true
  % code
endn2=310+k;
%%Extract 64 x 64 subframe from 1st frame 
row2=row1-n1;
col2=col1-n2;
subframe=zeros(100,100);
m1=1;
m2=1;
while m1<=100;
  while m2<=100;
      subframe(m1,m2)=im(row2,col2);
      col2=col2+1;
      m2=m2+1;
  end
  row2=row2+1;
  m1=m1+1;
 m2=1;
 col2=col1-n2;
end
subframe1=subframe;
%figure(4);
%imshow(subframe1,[]);
int_sumx=0;
x_cent=0;
row3=row1-n1;
col3=col1-n2;
z1=row3;z2=col3;
while z1<=(row3+100)
  while z2<=(col3+100)
      x_cent=x_cent+(im(z1,z2)*z1);
      int_sumx=int_sumx+im(z1,z2);
      z2=z2+1;
  end
  z1=z1+1;
  z2=col3;
end
x_int_cent=(x_cent/int_sumx);
int_sumy=0;
y_cent=0;
row3=row1-n1;
col3=col1-n2;
z1=row3;z2=col3;
while z1<=(col3+100)
  while z2<(row3+100)
      y_cent=y_cent+(im(z1,z2)*z2);
      int_sumy=int_sumy+im(z1,z2);
      z2=z2+1;
  end
  z1=z1+1;
  z2=col3;
end
y_int_cent=(y_cent/int_sumy);
% superimpose '+' on target and encircle it %
x=floor(x_int_cent);
y=floor(y_int_cent);
%a=im(x,y);
for p=(x-2):1:(x+2)
  im(p,y)=256;
end
for q=(y-2):1:(y+2)
  im(x,q)=256;
end
figure(2);
imshow(im,[]);colormap(gray);
k=k+1
    end

Answer 1

[Image Analyst]

Without your video file and more comments in your code, I'm not going to dive into that and debug it, especially when it's something you can do yourself. See http://blogs.mathworks.com/videos/2012/07/03/debugging-in-matlab/

My guess is that either p or y is zero like the error message says. Or else they're fractional numbers. See the FAQ:

http://matlab.wikia.com/wiki/FAQ#How_do_I_fix_the_error_.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22.3F