title: ValueError: Input 0 is incompatible with layer conv2d_5: expected ndim=4, found ndim=2
body: <p>I am trying to build a CNN network and wuld like to probe the layer dimention using output_shape.
  But it's giving me an error as follows:</p>
  
  <blockquote>
    <p>ValueError: Input 0 is incompatible with layer conv2d_5: expected ndim=4, found ndim=2</p>
  </blockquote>
  
  <p>Below is the code I am trying to execute</p>
  
  <pre><code>from keras.layers import Activation
  
  model = Sequential()
  model.add(Convolution2D(32, 3, 3, activation='relu', input_shape=(1,28,28)))
  
  print(model.output_shape)
  </code></pre>