title: Is there any way to iterate and take out 3d slices of a tensor?
body: <p>Is there a way to iterate over values of a 3D tensor for multiplication?
  I have a 3x3 mask that I want to multiply with each 3 dimensional pixels of an rgb image</p>
  
  <p>AN equivalent implementation is, say I have a 3x3 tensor which is a mask and a nonex200x200x3 rgb image. I want to multiply the 3x3 mask with the (r,g,b) value at (0,0,:) and then again with (0,1,:) and so on until (0,199,:) and then on to (1,0,:) all the way upto (199,199,:) to produce a (200,200,3) array.
  This is because each of 3x3 mask by 3x1 element is supposed to yield a 3x1 element (or a 3D pixel) for each of 200x200 pixels in the input image.</p>
  
  <p>slicing is easy enough in a numpy array since I can iterate using indices, but is there any way to do so in Keras?
  Any help is highly appreciated
  Thanks</p>
  
  <p>Keras.backend.dot is able to carry out the actual multiplication, but how to go about actually taking the slice?</p>