title: Using Keras' TensorBoard callback with `write_images=True`: save images less often
body: <p>I would like to fix issues regarding when the images are saved when using the tensorboard callback with <code>write_images=True</code>: 
  <a href="https://keras.io/callbacks/#tensorboard" rel="nofollow noreferrer">https://keras.io/callbacks/#tensorboard</a></p>
  
  <p>Could it be possible to plot a convnet's weights only at the end of the training with TensorBoard this way?</p>
  
  <p>Right now it seems like if TensorBoard wanted to save the images at every epochs, and the file sizes are getting really huge. I get something like 5 GB per epoch on the MNIST dataset and <a href="https://github.com/Vooban/Hyperopt-Keras-CNN-CIFAR-100" rel="nofollow noreferrer">this convolutional neural network</a> convnet) just to save those <code>write_images=True</code>. </p>
  
  <p>Right now the images are saved at a frequency of <code>histogram_freq=1</code> since I call it with the value of 1. But I want my histograms to be saved at every epoch or so rather than only at the end. </p>
  
  <p>Would using a second TensorBoard callback with a different frequency work, and if so, how?</p>
  
  <p>Also, I would like to discard the biases of the convolutions in this callback or to transpose them sideways, because those <code>63px x 1px</code> images are showing up enlarged 342 times in a way that they span 10 screens in height. And I am not sure how to interpret the convolutional kernels, they should be 3D considering the depth of the channels, not only monochrome 2D (I use the CIFAR-10 dataset). </p>