title: Matlab detectSURFFeatures() error: "Expected input number 1, I, to be two-dimensional."
body: <p>I'm following Matlab > Help guide "Object Detection in a Cluttered Scene Using Point Feature Matching" and detectSURFFeatures() gets error because it expects a 2-dimensional input argument.   .png doesn't work either.</p>
  
  <blockquote>
    <blockquote>
      <p>boxImage = imread('C:\WORK\images for feature matching\iPhone6p_back_clean.JPG');</p>
      
      <p>boxPoints = detectSURFFeatures(  boxImage );</p>
    </blockquote>
  </blockquote>
  
  <p>Error using detectSURFFeatures
  Expected input number 1, I, to be two-dimensional.</p>
  
  <p>Error in detectSURFFeatures>checkImage (line 124)
  validateattributes(I,{'logical', 'uint8', 'int16', 'uint16', ...</p>
  
  <p>Error in detectSURFFeatures (line 81)
  checkImage(I);</p>