Tensorflow：tensorflow 示例中 label_image.py 中的“input_mean”和“input_std”是什么

我使用的是 Windows 7。我已经使用官方再培训示例训练了一个 mobilenet。

https://github.com/tensorflow/tensorflow/tree/master/tensorflow/examples/image_retraining

我已经运行了这样的命令：

python ../tensorflow-master/tensorflow/examples/image_retraining/retrain.py --image_dir test/ --learning_rate=0.0001 --testing_percentage=20 --validation_percentage=20 --train_batch_size=32 --validation_batch_size=-1 --flip_left_right True --random_scale=30 --random_brightness=30 --eval_step_interval=100 --how_many_training_steps=2000 --architecture mobilenet_0.25_128

我得到了经过训练的图形和标签文件“output_graph.pb”和“output_labels.txt”。

现在，我想使用上面生成的图进行分类，所以我使用了tensorflow github中提供的label_image.py。

https://github.com/tensorflow/tensorflow/tree/master/tensorflow/examples/label_image

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import argparse
import sys

import numpy as np
import tensorflow as tf

def load_graph(model_file):
  graph = tf.Graph()
  graph_def = tf.GraphDef()

  with open(model_file, "rb") as f:
    graph_def.ParseFromString(f.read())
  with graph.as_default():
    tf.import_graph_def(graph_def)

  return graph

def read_tensor_from_image_file(file_name, input_height=299, input_width=299,
                input_mean=0, input_std=255):
  input_name = "file_reader"
  output_name = "normalized"
  file_reader = tf.read_file(file_name, input_name)
  if file_name.endswith(".png"):
    image_reader = tf.image.decode_png(file_reader, channels = 3,
                                       name='png_reader')
  elif file_name.endswith(".gif"):
    image_reader = tf.squeeze(tf.image.decode_gif(file_reader,
                                                  name='gif_reader'))
  elif file_name.endswith(".bmp"):
    image_reader = tf.image.decode_bmp(file_reader, name='bmp_reader')
  else:
    image_reader = tf.image.decode_jpeg(file_reader, channels = 3,
                                        name='jpeg_reader')
  float_caster = tf.cast(image_reader, tf.float32)
  dims_expander = tf.expand_dims(float_caster, 0);
  resized = tf.image.resize_bilinear(dims_expander, [input_height, input_width])
  normalized = tf.divide(tf.subtract(resized, [input_mean]), [input_std])
  sess = tf.Session()
  result = sess.run(normalized)

  return result

def load_labels(label_file):
  label = []
  proto_as_ascii_lines = tf.gfile.GFile(label_file).readlines()
  for l in proto_as_ascii_lines:
    label.append(l.rstrip())
  return label

if __name__ == "__main__":
  file_name = "tensorflow/examples/label_image/data/grace_hopper.jpg"
  model_file = \
    "tensorflow/examples/label_image/data/inception_v3_2016_08_28_frozen.pb"
  label_file = "tensorflow/examples/label_image/data/imagenet_slim_labels.txt"
  input_height = 299
  input_width = 299
  input_mean = 0
  input_std = 255
  input_layer = "input"
  output_layer = "InceptionV3/Predictions/Reshape_1"

  parser = argparse.ArgumentParser()
  parser.add_argument("--image", help="image to be processed")
  parser.add_argument("--graph", help="graph/model to be executed")
  parser.add_argument("--labels", help="name of file containing labels")
  parser.add_argument("--input_height", type=int, help="input height")
  parser.add_argument("--input_width", type=int, help="input width")
  parser.add_argument("--input_mean", type=int, help="input mean")
  parser.add_argument("--input_std", type=int, help="input std")
  parser.add_argument("--input_layer", help="name of input layer")
  parser.add_argument("--output_layer", help="name of output layer")
  args = parser.parse_args()

  if args.graph:
    model_file = args.graph
  if args.image:
    file_name = args.image
  if args.labels:
    label_file = args.labels
  if args.input_height:
    input_height = args.input_height
  if args.input_width:
    input_width = args.input_width
  if args.input_mean:
    input_mean = args.input_mean
  if args.input_std:
    input_std = args.input_std
  if args.input_layer:
    input_layer = args.input_layer
  if args.output_layer:
    output_layer = args.output_layer

  graph = load_graph(model_file)
  t = read_tensor_from_image_file(file_name,
                                  input_height=input_height,
                                  input_width=input_width,
                                  input_mean=input_mean,
                                  input_std=input_std)

  input_name = "import/" + input_layer
  output_name = "import/" + output_layer
  input_operation = graph.get_operation_by_name(input_name);
  output_operation = graph.get_operation_by_name(output_name);

  with tf.Session(graph=graph) as sess:
    results = sess.run(output_operation.outputs[0],
                      {input_operation.outputs[0]: t})
  results = np.squeeze(results)

  top_k = results.argsort()[-5:][::-1]
  labels = load_labels(label_file)
  for i in top_k:
    print(labels[i], results[i])

我运行以下命令：

python ../tensorflow-master/tensorflow/examples/label_image/label_image.py --graph=output_graph.pb --labels=output_labels.txt --image=test.jpg --input_layer=input --output_layer=final_result --input_mean=128 --input_std=128 --input_width=128 --input_height=128

并且可以对图像“test.jpg”进行分类。

但是，当我为“input_mean”和“input_std”使用不同的值时，结果会发生变化。

“input_mean”和“input_std”有什么用？以及如何获得这两个参数的正确值？