v.1 [Python3]

import numpy as np
from keras.models import Sequential
from keras.datasets import mnist # 60,000 28x28 grayscale images of 10 digits, + 10,000 test images
from keras.layers import Dense, Conv2D, MaxPooling2D, Flatten
from keras.utils import plot_model, to_categorical
from keras.preprocessing.image import load_img
from keras import backend as k


""" Import Data/Preprocess - (minimal for this highly prepared data set) """
(x_train, y_train), (x_test, y_test) = mnist.load_data()
# returns two tuples
    # x_train, x_test tuple (uint8) grayscale images with shape (num_samples * 28 * 28) num_samples = 60,000
    # y_train, y_test tuple (uint8) array of digit labels (0-9) with shape (num_samples)

mnist_width, mnist_height = 28, 28
num_classes = 10 # 0-9 for MNIST
batch_size = 64
epochs = 1

# input shape; differs based on configuration of imaga_data_format file. diff. per comp.
if k.image_data_format() == 'channels_first' :
    x_train = ((x_train.reshape(x_train.shape[0], 1, mnist_width, mnist_height)).astype('float32')) / 255
      # divide by 255 to get a 0-1 value for the color of a pixel (by default on a 0-255 scale, 0 white, 255 black)
    x_test = ((x_test.reshape(x_train.shape[0], 1, mnist_width, mnist_height)).astype('float32')) / 255
    input_shape = (1, mnist_width, mnist_height) # 1 channel, BW image

else : # by default channels is last; this is a configuration setting in backend
    x_train = ((x_train.reshape(x_train.shape[0], mnist_width, mnist_height, 1)).astype('float32')) / 255
    x_test = ((x_test.reshape(x_test.shape[0], mnist_width, mnist_height, 1)).astype('float32')) / 255
    input_shape = (mnist_width, mnist_height, 1)

"""This is how the data is organized"""
print('x_train shape:', x_train.shape)
print(x_train.shape[0], 'train samples')
print(x_test.shape[0], 'test samples')
print('y_train shape:', y_train.shape)
print(y_train.shape[0], 'train samples')
print(y_test.shape[0], 'test samples')


y_train = to_categorical(y_train, num_classes=num_classes)
y_test = to_categorical(y_test, num_classes=num_classes)

""" The CNN architecture """
# Model_CNN map/checklist:
    # input data *
    # conv. layer + ReLu *
    # pool layer *
    # conv. layer + ReLu *
    # pooling *
    # fully connected *
    # fully connected *
    # out *
    
model = Sequential()

num_input_filters = 32 # need help understanding justification
conv_kernel_size_d1, conv_kernel_size_d2 = 4, 4 # recommended from tutorial

# first conv. layer
convolution_1 = Conv2D(
    num_input_filters,
    (conv_kernel_size_d1, conv_kernel_size_d2),
    strides=(2, 2), # magic number; no justification, assuming units is pixels
    activation='relu',
    input_shape=input_shape
)
model.add(convolution_1)

# first pooling
maxPooling_1 = MaxPooling2D(pool_size=(2,2), strides=(2,2))
model.add(maxPooling_1)

# second conv. layer
convolution_2 = Conv2D(
    (2 * num_input_filters),
    (conv_kernel_size_d1, conv_kernel_size_d2),
    strides=(2,2),
    activation='relu'
    # input shape should be default?
)
model.add(convolution_2)

# second pooling
maxPooling_2 = MaxPooling2D(pool_size=(2, 2), strides=(2,2))
model.add(maxPooling_2)

# first FC (dense)
flatten_1 = Flatten()
model.add(flatten_1)

# first dense
dense_1 = Dense(64, activation='relu')
model.add(dense_1)

# second dense
dense_2 = Dense(10, activation='softmax')
model.add(dense_2)

# a couple visualization tools
model.summary() # provides summary of model (output shape, total paramters)
# plot_model(model, to_file='UNIQUE-NAME.png', show_shapes=True) # plots model? # these require additional software
# load_img('UNIQUE-NAME.png')

""" Loss Function/nonlinear equation to be solved"""
model.compile(optimizer='adam',
              loss = 'categorical_crossentropy',
              metrics=['accuracy']
)

model.fit(x=x_train, y=y_train, batch_size=batch_size, epochs=epochs, verbose=0, validation_data=(x_test, y_test))


evaluation = model.evaluate(x=x_test, y=y_test, batch_size=batch_size, verbose=0)
print('Test loss: ', evaluation[0])
print('Test accuracy: ', evaluation[1])

"""
Sources: 
https://keras.io/getting-started/sequential-model-guide/
https://github.com/keras-team/keras/blob/master/examples/mnist_cnn.py
https://www.coursera.org/learn/ai/lecture/C6sN7/feed-forward-networks
+ Misc. referenced elsewhere
"""