title: Python 3 throws name 'InputLayer' is not defined when trying to add tensorflow input layer
body: <p>I've been trying to implement a simple network which takes images of varying sizes and colorizes them. I've been trying to use an input layer with this model, but it seems that python has "changed its mind" since I last worked on this project, and no longer recognises InputLayer</p>
  
  <p>I've checked my imports for malformed library names, and no errors have been thrown. What has changed since I ran this code last and what should I change about what I have now? For context, I'm using the newest version of tensorflow and all other libraries on python 3. I don't remember how I last ran this script, but it appears to have been on a legacy version of at least one of the libraries I'm using. </p>
  
  <p>My imports:</p>
  
  <pre><code>from skimage import color
  import numpy as np
  import tensorflow as tf
  import tensorflow.keras.backend as K
  import matplotlib.pyplot as plt
  %matplotlib inline
  from keras.datasets import mnist
  from tensorflow.keras.layers import Dense, Flatten, MaxPooling2D, BatchNormalization,UpSampling2D,Conv2DTranspose,Add,AvgPool2D
  from keras.layers.convolutional import Conv2D
  from tensorflow.keras import Sequential
  from tensorflow.keras.models import Sequential, Model
  from tensorflow.keras.regularizers import l2
  import sys
  !pip install opencv-python
  import cv2
  from os.path import isfile, join
  </code></pre>
  
  <p>The area causing errors:</p>
  
  <pre><code>colormodel = Sequential()
  colormodel.add(InputLayer(input_shape=(None, None, 1)))
  </code></pre>
  
  <p>If anything else is needed of me, please comment what I've left out</p>
  
  <p>I've revieved this error message when trying to load in the code block on jupyter notebook:</p>
  
  <pre><code>NameError                                 Traceback (most recent call last)
  
  &lt;ipython-input-21-13604e43d8ef&gt; in &lt;module&gt;()
        1 colormodel = Sequential()
  ----&gt; 2 colormodel.add(InputLayer(input_shape=(None, None, 1)))
        3 colormodel.add(Conv2D(8, (3, 3), activation='relu', padding='same', strides=2))
        4 colormodel.add(Conv2D(8, (3, 3), activation='relu', padding='same'))
        5 colormodel.add(Conv2D(16, (3, 3), activation='relu', padding='same'))
  
  NameError: name 'InputLayer' is not defined
  </code></pre>