title: Crop a 3D image
body: <p>I have an image of size <em>512</em>-by-<em>614</em>-by-<em>196</em>, with <em>196</em> bands or channels.
  I want to crop it to a <em>50</em>-by-<em>50</em>-by-<em>196</em> sub-image,
  I used <code>imcrop</code> but the result is a sub-image that is <em>50</em>-by-<em>50</em>. How can I crop the original image to be <em>50</em>-by-<em>50</em>-by-<em>196</em>?</p>