Warning('OFF','all') does nothing?

In my code I put:

warning('OFF','all')

and then I read some images and display them in a figure from within a loop. Every single iteration I get the WARNING message below. What is the point of the warning off command if I get a warning anyway?? I've tried various combinations of the above command and I get the error no matter what.

Warning: Image is too big to fit on screen; displaying at 67% 
> In images.internal.initSize (line 71)
  In imshow (line 336)
  In MyDir (line 48)