Can't understand the warning

Hi, My code works but every time it runs through line 13 it writes on the command window :"Warning: Integer operands are required for colon operator when used as index ". The relevant part of my code looks like that:

   filename = uigetfile;
   obj = mmreader(filename);
   nFrames=obj.NumberOfFrames;
   for k = 1 : nFrames  
   this_frame = read(obj, k);
   thisfig = figure();
   thisax = axes('Parent', thisfig);
   image(this_frame, 'Parent', thisax);
   if k==1
      handle=imrect;
      pos=handle.getPosition;
   end
   partOf=this_frame(pos(2):pos(2)+pos(4),pos(1):pos(1)+pos(3));%this is line 13
   vector(k)=mean2(partOf);
  title(thisax, sprintf('Frame #%d', k));
   end

Why this warning appears and can i ignore it?

[EDITED, Code formatted, Jan]

Answer 1

[Jan]

Indices must have positive integer values for obvious reasons. If any value of pos is not integer, this warning appears and you should fix this depending on your needs. Perhaps pos = round(pos) is a suitable solution, but floor or ceil are possible also.

[Maayan]

Thanks! That solves the problem.

Answer 2

[Walter Roberson]

Why are you assuming tat handle.getPosition is always going to return integers ? Have a closer look at the values in "pos".

You have not defined any axis Position or xlim or ylim, so the axis is going to be whatever size it happens to default to.

You will find the result to be different if you add the command

axes(thisax, 'image')

after your image() call.