This sample trains an "MNIST" handwritten digit recognition model on a GPU or TPU backend using a Keras model. Data are handled using the tf.data.Datset API. This is a very simple sample provided for educational purposes. Do not expect outstanding TPU performance on a dataset as small as MNIST.
In [1]:
BATCH_SIZE = 64
LEARNING_RATE = 0.002
# GCS bucket for training logs and for saving the trained model
# You can leave this empty for local saving, unless you are using a TPU.
# TPUs do not have access to your local instance and can only write to GCS.
BUCKET="" # a valid bucket name must start with gs://
training_images_file = 'gs://mnist-public/train-images-idx3-ubyte'
training_labels_file = 'gs://mnist-public/train-labels-idx1-ubyte'
validation_images_file = 'gs://mnist-public/t10k-images-idx3-ubyte'
validation_labels_file = 'gs://mnist-public/t10k-labels-idx1-ubyte'
In [2]:
import os, re, math, json, time
import PIL.Image, PIL.ImageFont, PIL.ImageDraw
import numpy as np
import tensorflow as tf
from matplotlib import pyplot as plt
from tensorflow.python.platform import tf_logging
print("Tensorflow version " + tf.__version__)
In [3]:
try: # detect TPUs
tpu = tf.distribute.cluster_resolver.TPUClusterResolver() # TPU detection
tf.config.experimental_connect_to_cluster(tpu)
tf.tpu.experimental.initialize_tpu_system(tpu)
strategy = tf.distribute.experimental.TPUStrategy(tpu)
except ValueError: # detect GPUs
strategy = tf.distribute.MirroredStrategy() # for GPU or multi-GPU machines
#strategy = tf.distribute.get_strategy() # default strategy that works on CPU and single GPU
#strategy = tf.distribute.experimental.MultiWorkerMirroredStrategy() # for clusters of multi-GPU machines
print("Number of accelerators: ", strategy.num_replicas_in_sync)
# adjust batch size and learning rate for distributed computing
global_batch_size = BATCH_SIZE * strategy.num_replicas_in_sync # num replcas is 8 on a single TPU or N when runing on N GPUs.
learning_rate = LEARNING_RATE * strategy.num_replicas_in_sync
In [4]:
#@title visualization utilities [RUN ME]
"""
This cell contains helper functions used for visualization
and downloads only. You can skip reading it. There is very
little useful Keras/Tensorflow code here.
"""
# Matplotlib config
plt.rc('image', cmap='gray_r')
plt.rc('grid', linewidth=0)
plt.rc('xtick', top=False, bottom=False, labelsize='large')
plt.rc('ytick', left=False, right=False, labelsize='large')
plt.rc('axes', facecolor='F8F8F8', titlesize="large", edgecolor='white')
plt.rc('text', color='a8151a')
plt.rc('figure', facecolor='F0F0F0')# Matplotlib fonts
MATPLOTLIB_FONT_DIR = os.path.join(os.path.dirname(plt.__file__), "mpl-data/fonts/ttf")
# pull a batch from the datasets. This code is not very nice, it gets much better in eager mode (TODO)
def dataset_to_numpy_util(training_dataset, validation_dataset, N):
# get one batch from each: 10000 validation digits, N training digits
unbatched_train_ds = training_dataset.unbatch()
# This is the TF 2.0 "eager execution" way of iterating through a tf.data.Dataset
for v_images, v_labels in validation_dataset:
break
for t_images, t_labels in unbatched_train_ds.batch(N):
break
validation_digits = v_images.numpy()
validation_labels = v_labels.numpy()
training_digits = t_images.numpy()
training_labels = t_labels.numpy()
# these were one-hot encoded in the dataset
validation_labels = np.argmax(validation_labels, axis=1)
training_labels = np.argmax(training_labels, axis=1)
return (training_digits, training_labels,
validation_digits, validation_labels)
# create digits from local fonts for testing
def create_digits_from_local_fonts(n):
font_labels = []
img = PIL.Image.new('LA', (28*n, 28), color = (0,255)) # format 'LA': black in channel 0, alpha in channel 1
font1 = PIL.ImageFont.truetype(os.path.join(MATPLOTLIB_FONT_DIR, 'DejaVuSansMono-Oblique.ttf'), 25)
font2 = PIL.ImageFont.truetype(os.path.join(MATPLOTLIB_FONT_DIR, 'STIXGeneral.ttf'), 25)
d = PIL.ImageDraw.Draw(img)
for i in range(n):
font_labels.append(i%10)
d.text((7+i*28,0 if i<10 else -4), str(i%10), fill=(255,255), font=font1 if i<10 else font2)
font_digits = np.array(img.getdata(), np.float32)[:,0] / 255.0 # black in channel 0, alpha in channel 1 (discarded)
font_digits = np.reshape(np.stack(np.split(np.reshape(font_digits, [28, 28*n]), n, axis=1), axis=0), [n, 28*28])
return font_digits, font_labels
# utility to display a row of digits with their predictions
def display_digits(digits, predictions, labels, title, n):
plt.figure(figsize=(13,3))
digits = np.reshape(digits, [n, 28, 28])
digits = np.swapaxes(digits, 0, 1)
digits = np.reshape(digits, [28, 28*n])
plt.yticks([])
plt.xticks([28*x+14 for x in range(n)], predictions)
for i,t in enumerate(plt.gca().xaxis.get_ticklabels()):
if predictions[i] != labels[i]: t.set_color('red') # bad predictions in red
plt.imshow(digits)
plt.grid(None)
plt.title(title)
# utility to display multiple rows of digits, sorted by unrecognized/recognized status
def display_top_unrecognized(digits, predictions, labels, n, lines):
idx = np.argsort(predictions==labels) # sort order: unrecognized first
for i in range(lines):
display_digits(digits[idx][i*n:(i+1)*n], predictions[idx][i*n:(i+1)*n], labels[idx][i*n:(i+1)*n],
"{} sample validation digits out of {} with bad predictions in red and sorted first".format(n*lines, len(digits)) if i==0 else "", n)
In [5]:
#IS_COLAB_BACKEND = 'COLAB_GPU' in os.environ # this is always set on Colab, the value is 0 or 1 depending on GPU presence
#if IS_COLAB_BACKEND:
# from google.colab import auth
# auth.authenticate_user() # Authenticates the backend and also the TPU using your credentials so that they can access your private GCS buckets
Please read the best practices for building input pipelines with tf.data.Dataset
In [6]:
def read_label(tf_bytestring):
label = tf.io.decode_raw(tf_bytestring, tf.uint8)
label = tf.reshape(label, [])
label = tf.one_hot(label, 10)
return label
def read_image(tf_bytestring):
image = tf.io.decode_raw(tf_bytestring, tf.uint8)
image = tf.cast(image, tf.float32)/256.0
image = tf.reshape(image, [28*28])
return image
def load_dataset(image_file, label_file):
imagedataset = tf.data.FixedLengthRecordDataset(image_file, 28*28, header_bytes=16)
imagedataset = imagedataset.map(read_image, num_parallel_calls=16)
labelsdataset = tf.data.FixedLengthRecordDataset(label_file, 1, header_bytes=8)
labelsdataset = labelsdataset.map(read_label, num_parallel_calls=16)
dataset = tf.data.Dataset.zip((imagedataset, labelsdataset))
return dataset
def get_training_dataset(image_file, label_file, batch_size):
dataset = load_dataset(image_file, label_file)
dataset = dataset.cache() # this small dataset can be entirely cached in RAM, for TPU this is important to get good performance from such a small dataset
dataset = dataset.shuffle(5000, reshuffle_each_iteration=True)
dataset = dataset.repeat() # Mandatory for Keras for now
dataset = dataset.batch(batch_size, drop_remainder=True) # drop_remainder is important on TPU, batch size must be fixed
dataset = dataset.prefetch(-1) # fetch next batches while training on the current one (-1: autotune prefetch buffer size)
return dataset
def get_validation_dataset(image_file, label_file):
dataset = load_dataset(image_file, label_file)
dataset = dataset.cache() # this small dataset can be entirely cached in RAM, for TPU this is important to get good performance from such a small dataset
dataset = dataset.repeat() # Mandatory for Keras for now
dataset = dataset.batch(10000, drop_remainder=True) # 10000 items in eval dataset, all in one batch
return dataset
# instantiate the datasets
training_dataset = get_training_dataset(training_images_file, training_labels_file, global_batch_size)
validation_dataset = get_validation_dataset(validation_images_file, validation_labels_file)
In [ ]:
N = 24
(training_digits, training_labels,
validation_digits, validation_labels) = dataset_to_numpy_util(training_dataset, validation_dataset, N)
display_digits(training_digits, training_labels, training_labels, "training digits and their labels", N)
display_digits(validation_digits[:N], validation_labels[:N], validation_labels[:N], "validation digits and their labels", N)
font_digits, font_labels = create_digits_from_local_fonts(N)
In [ ]:
# This model trains to 99.4%— sometimes 99.5%— accuracy in 10 epochs (with a batch size of 64)
def make_model():
model = tf.keras.Sequential(
[
tf.keras.layers.Reshape(input_shape=(28*28,), target_shape=(28, 28, 1)),
tf.keras.layers.Conv2D(filters=6, kernel_size=3, padding='same', use_bias=True, activation='relu'),
tf.keras.layers.Conv2D(filters=12, kernel_size=6, padding='same', use_bias=True, activation='relu', strides=2),
tf.keras.layers.Conv2D(filters=24, kernel_size=6, padding='same', use_bias=True, activation='relu', strides=2),
tf.keras.layers.Flatten(),
tf.keras.layers.Dense(200, use_bias=True, activation='relu'),
tf.keras.layers.Dense(10, activation='softmax')
])
model.compile(optimizer='adam', # learning rate will be set by LearningRateScheduler
loss='categorical_crossentropy',
metrics=['accuracy'])
return model
with strategy.scope(): # the new way of handling distribution strategies in Tensorflow 1.14+
model = make_model()
# print model layers
model.summary()
# set up Tensorboard logs
timestamp = time.strftime("%Y-%m-%d-%H-%M-%S")
log_dir=os.path.join(BUCKET, 'mnist-logs', timestamp)
tb_callback = tf.keras.callbacks.TensorBoard(log_dir=log_dir, update_freq=50*global_batch_size)
print("Tensorboard loggs written to: ", log_dir)
In [ ]:
EPOCHS = 10
steps_per_epoch = 60000//global_batch_size # 60,000 items in this dataset
print("Step (batches) per epoch: ", steps_per_epoch)
history = model.fit(training_dataset, steps_per_epoch=steps_per_epoch, epochs=EPOCHS,
validation_data=validation_dataset, validation_steps=1,
callbacks=[tb_callback], verbose=1)
In [ ]:
# recognize digits from local fonts
probabilities = model.predict(font_digits, steps=1)
predicted_labels = np.argmax(probabilities, axis=1)
display_digits(font_digits, predicted_labels, font_labels, "predictions from local fonts (bad predictions in red)", N)
# recognize validation digits
probabilities = model.predict(validation_digits, steps=1)
predicted_labels = np.argmax(probabilities, axis=1)
display_top_unrecognized(validation_digits, predicted_labels, validation_labels, N, 7)
author: Martin Gorner
twitter: @martin_gorner
Copyright 2020 Google LLC
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
This is not an official Google product but sample code provided for an educational purpose