title: applying an image filtering technique on 'selected' pixels in MATLAB
body: <p>The feature extraction step of my algorithm, applies some filter on a "3D" image and use the value of filtered pixels as the feature of original pixels of image.</p>
  
  <p>My problem is that I need the feature of only small subset of pixels(threshold-ed pixels), not all of the image. and it is time consuming to filter all of the image, instead of only some pixels.</p>
  
  <p>My question is how can I filter only selected pixels of an image? Is there any matlab function for this purpose?(I think I can not use imfilter)</p>
  
  <p>Thank you.</p>