title: DCT of an image in octave
body: <p>Acording to Octave <a href="http://octave.sourceforge.net/signal/function/dct2.html" rel="nofollow">documentation for dct2</a>,  <code>dct2 (x)</code> Computes the 2-D discrete cosine transform of matrix <code>x</code> but when I have tried this following code I am getting an error, what can I possibly doing wrong? </p>
  
  <pre><code>A= imread('img.jpg')
  [m,n]=size(A)
  B=dct2(A)
  </code></pre>
  
  <p>it returns an error that:</p>
  
  <pre><code>ERROR: 'dct2' undefined near line 4 column 3
  </code></pre>
  
  <p>I have tried checking whether <code>A</code> is a matrix or not, and its a matrix, so where is the bug? I am using OCtave 3.2.4 on windows.</p>