Given frame_logits from a per-pixel softmax, generate colors.

def pixels_from_softmax(frame_logits, pure_sampling=False,
                        temperature=1.0, gumbel_noise_factor=0.2):
  """Given frame_logits from a per-pixel softmax, generate colors."""
  # If we're purely sampling, just sample each pixel.
  if pure_sampling or temperature == 0.0:
    return common_layers.sample_with_temperature(frame_logits, temperature)

  # Gumbel-sample from the pixel sofmax and average by pixel values.
  pixel_range = tf.to_float(tf.range(256))
  for _ in range(len(frame_logits.get_shape().as_list()) - 1):
    pixel_range = tf.expand_dims(pixel_range, axis=0)

  frame_logits = tf.nn.log_softmax(frame_logits)
  gumbel_samples = discretization.gumbel_sample(
      common_layers.shape_list(frame_logits)) * gumbel_noise_factor

  frame = tf.nn.softmax((frame_logits + gumbel_samples) / temperature, axis=-1)
  result = tf.reduce_sum(frame * pixel_range, axis=-1)
  # Round on the forward pass, not on the backward one.
  return result + tf.stop_gradient(tf.round(result) - result)