# Mnist handwritten digit classification using tensorflow

Milind Soorya / September 16, 2021

## Introduction

### What is Handwritten Digit Recognition?

Handwritten digit recognition is the ability of computers to recognize human handwritten digits. It is a hard task for the machine because handwritten digits are not perfect and can vary from person to person. Handwritten digit recognition is the solution to this problem which uses the image of a digit and recognizes the digit present in the image.

### The MNIST dataset

This is probably one of the most popular datasets among machine learning and deep learning enthusiasts. The MNIST dataset contains 60,000 training images of handwritten digits from zero to nine and 10,000 images for testing. So, the MNIST dataset has 10 different classes. The handwritten digits images are represented as a 28×28 matrix where each cell contains grayscale pixel value.

In this article, we will look at the MNIST dataset and create a simple neural network using TensorFlow and Keras. Later we will also add a hidden layer to make the model more accurate.

## TLDR; MNIST handwritten digit classification github

Here for the code? You can find the python Notebook in my GitHub.

## Import the modules

``import tensorflow as tffrom tensorflow import kerasimport matplotlib.pyplot as plt%matplotlib inlineimport numpy as np``

## Load the MNIST dataset from Keras

``````(x_train, y_train), (x_test, y_test) = keras.datasets.mnist.load_data()
len(x_train)# 60000
len(x_test)# 10000
# Finding the shape of individual samplex_train[0].shape# (28, 28)``````

hence, each sample is a 28x28 pixel image

``x_train[0]``

The value ranges 0-255. `0` means the pixel at that point has no intensity and `255` has the highest intensity.

## See the images

``plt.matshow(x_train[0])``
``````y_train[0]
# 5``````
``````# Show first 5 datay_train[:5]
# array([5, 0, 4, 1, 9], dtype=uint8)``````

## Flatten the training data

we need to convert the two-dimensional input data into a single-dimensional format for feeding into the model. This is achieved by a process called flattening. In this process, the 28x28 grid image is converted into a single-dimensional array of 784(28x28).

``````x_train.shape
#  (60000, 28, 28)``````
``# Scale the data so that the values are from 0 - 1x_train = x_train / 255x_test = x_test / 255``
``x_train[0]``
``# Flattening the train and test datax_train_flattened = x_train.reshape(len(x_train), 28*28)x_test_flattened = x_test.reshape(len(x_test), 28*28)``
``````x_train_flattened.shape
# (60000, 784)``````
``````x_train_flattened.shape
# (60000, 784)``````

## PART 1 - Create a simple neural network in Keras

In this step, we will create the most simple, single-layer neural network using Keras.

``````# Sequential create a stack of layersmodel = keras.Sequential([    keras.layers.Dense(10, input_shape=(784,), activation='sigmoid')])
# Optimizer will help in backproagation to reach better global optimamodel.compile(    optimizer='adam',    loss='sparse_categorical_crossentropy',    metrics=['accuracy'])
# Does the trainingmodel.fit(x_train_flattened, y_train, epochs=5)``````
``````# OUTPUT
Epoch 1/5    1875/1875 [==============================] - 3s 2ms/step - loss: 0.4659 - accuracy: 0.8784    Epoch 2/5    1875/1875 [==============================] - 3s 1ms/step - loss: 0.3040 - accuracy: 0.9145    Epoch 3/5    1875/1875 [==============================] - 3s 1ms/step - loss: 0.2828 - accuracy: 0.9206    Epoch 4/5    1875/1875 [==============================] - 3s 1ms/step - loss: 0.2733 - accuracy: 0.9234    Epoch 5/5    1875/1875 [==============================] - 3s 1ms/step - loss: 0.2667 - accuracy: 0.9259``````

After the training, I got an accuracy of around 92%, which is not bad considering we created a single-layer neural network.

## Evaluate the accuracy of test data

``model.evaluate(x_test_flattened, y_test)``
``# OUTPUT313/313 [==============================] - 1s 1ms/step - loss: 0.2702 - accuracy: 0.9241``

So, we were able to get an accuracy of 92% with the test data.

## Sample prediction

We will now visualize the result by showing the image and making the prediction and validating it.

``# Show the imageplt.matshow(x_test[0])``
``````# Make the predictionsy_predicted = model.predict(x_test_flattened)y_predicted[0]
array([1.8693238e-02, 2.5351633e-07, 3.8469851e-02, 9.5759392e-01,           2.0694137e-03, 1.0928032e-01, 1.0289272e-06, 9.9976790e-01,           6.6316605e-02, 6.9463903e-01], dtype=float32)
``````
``````# Find the maximum value using numpynp.argmax(y_predicted[0])
# 7``````
``````# converting y_predicted from whole numbers to integers# so that we can use it in confusion matrix# In short we are argmaxing the entire predictiony_predicted_labels = [np.argmax(i) for i in y_predicted]y_predicted_labels[:5]
# [7, 2, 1, 0, 4]``````

## Using confusion matrix for validation

If you are confused about the confusion matrix, read this small article before proceeding - The ultimate guide to confusion matrix in machine learning

``cm = tf.math.confusion_matrix(labels=y_test, predictions=y_predicted_labels)cm``
``# OUTPUT <tf.Tensor: shape=(10, 10), dtype=int32, numpy=    array([[ 965,    0,    0,    2,    0,    4,    5,    2,    2,    0],           [   0, 1109,    3,    2,    1,    1,    4,    2,   13,    0],           [   7,    9,  905,   27,    8,    4,   13,   10,   44,    5],           [   3,    0,   12,  930,    0,   26,    2,   10,   16,   11],           [   1,    1,    4,    2,  906,    0,   11,    4,    9,   44],           [  10,    1,    1,   41,    8,  772,   14,    6,   31,    8],           [  13,    3,    5,    2,    7,   15,  909,    2,    2,    0],           [   1,    5,   20,   11,    7,    0,    0,  943,    2,   39],           [   7,    7,    5,   26,    9,   22,    8,   11,  867,   12],           [  11,    6,    1,   12,   21,    5,    0,   14,    4,  935]],          dtype=int32)>``

## Using seaborn to make confusion matrix look good

``import seaborn as snplt.figure(figsize = (10,7))sn.heatmap(cm, annot=True, fmt='d')plt.xlabel('Predicted')plt.ylabel('Truth')``

The confusion matrix gives a clear picture of our prediction.

## How to read the confusion matrix?

• All the diagonal elements are correct predictions, for example, we correctly predicted the number 0, 958 times.
• The black cells, value shows the wrong predictions. For each number n in the cell, it means that we predicted the value in the truth row as the value is the predicted column, n times. For Example, 3 was predicted as 2, 17 times.

## PART 2 - Adding a hidden layer

``````# Sequential create a stack of layers# Create a hidden layer with 100 neurons and relu activationmodel = keras.Sequential([    keras.layers.Dense(100, input_shape=(784,), activation='relu'),    keras.layers.Dense(10, activation='sigmoid')])
# Optimizer will help in backproagation to reach better global optimamodel.compile(    optimizer='adam',    loss='sparse_categorical_crossentropy',    metrics=['accuracy'])
# Does the trainingmodel.fit(x_train_flattened, y_train, epochs=5)``````
``    Epoch 1/5    1875/1875 [==============================] - 5s 2ms/step - loss: 0.2785 - accuracy: 0.9202    Epoch 2/5    1875/1875 [==============================] - 5s 2ms/step - loss: 0.1278 - accuracy: 0.9624    Epoch 3/5    1875/1875 [==============================] - 4s 2ms/step - loss: 0.0904 - accuracy: 0.9731    Epoch 4/5    1875/1875 [==============================] - 4s 2ms/step - loss: 0.0677 - accuracy: 0.9796    Epoch 5/5    1875/1875 [==============================] - 4s 2ms/step - loss: 0.0542 - accuracy: 0.9835``

## Evaluate the accuracy of the test set

``````model.evaluate(x_test_flattened, y_test)

313/313 [==============================] - 1s 1ms/step - loss: 0.0769 - accuracy: 0.9759``````

Now we can observe that by adding a hidden layer the accuracy increased from 92% to 97%.

## Using confusion matrix for validation

``````y_predicted = model.predict(x_test_flattened)y_predicted_labels = [np.argmax(i) for i in y_predicted]
cm = tf.math.confusion_matrix(labels=y_test, predictions=y_predicted_labels)
import seaborn as snplt.figure(figsize = (10,7))sn.heatmap(cm, annot=True, fmt='d')plt.xlabel('Predicted')plt.ylabel('Truth')``````

Compared to the previous confusion matrix the wrong predictions has gone down. We can see that the diagonal values have increased and the values in black cells have gone down. There are more '0' valued black cells, meaning correct predictions.

## Bonus Content

flattening out data each time is really tedious, don't worry keras got you covered. Just use the `keras.layers.Flatten` like the example below

``````# Flattening data using keras Flatten classmodel = keras.Sequential([    keras.layers.Flatten(input_shape=(28,28)),    keras.layers.Dense(100, activation='relu'),    keras.layers.Dense(10, activation='sigmoid')])
model.fit(x_train_flattened, y_train, epochs=5)``````
``    Epoch 1/5    1875/1875 [==============================] - 5s 2ms/step - loss: 0.2693 - accuracy: 0.9243    Epoch 2/5    1875/1875 [==============================] - 5s 2ms/step - loss: 0.1230 - accuracy: 0.9637    Epoch 3/5    1875/1875 [==============================] - 4s 2ms/step - loss: 0.0851 - accuracy: 0.9747    Epoch 4/5    1875/1875 [==============================] - 4s 2ms/step - loss: 0.0644 - accuracy: 0.9803    Epoch 5/5    1875/1875 [==============================] - 4s 2ms/step - loss: 0.0508 - accuracy: 0.9846``

## Next step

Try playing around with different activation functions, optimizers, loss functions and epochs to optimize the model. In case of doubt ping me on Twitter

## Conclusion

In this article, I discussed how to tackle the MNIST Digit Recognition problem by creating a simple Neural Network.

As a next step, I will do the same problem using Convoluted Neural Network(CNN), to read that as soon as it drops, please follow me on Twitter.

Thanks again for reading, have a nice day.

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