Data Science and Artificial Intelligence

Principal Component Analysis Case Study 2

Case Study on Implementing PCA for Face Recognition


#Import tools and libraries
from __future__ import print_function
from time import time
import matplotlib.pyplot as plt
from sklearn.model_selection import train_test_split
from sklearn.datasets import fetch_lfw_people
from sklearn.metrics import classification_report
from sklearn.metrics import confusion_matrix
from sklearn.decomposition import PCA
from sklearn import metrics
import pandas as pd
from sklearn.linear_model import LogisticRegression
from sklearn.preprocessing import StandardScaler
import numpy as np

# Download the data, if not already on disk and load it as numpy arrays
lfw_people = fetch_lfw_people(min_faces_per_person=70, resize=0.4)
# introspect the images arrays to find the shapes (for plotting)
n_samples, h, w = lfw_people.images.shape
# for machine learning we use the 2 data directly (as relative pixel positions info is ignored by this # model)
X =
n_features = X.shape[1]
# the label to predict is the id of the person
y =
target_names = lfw_people.target_names
n_classes = target_names.shape[0]
print("Total dataset size:")
print("n_samples: %d" % n_samples)
print("n_features: %d" % n_features)
print("n_classes: %d" % n_classes)


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Total dataset size:

n_samples:   1288

n_features:  1850

n_classes:           7


# Split into a training set and a test set using a stratified k fold
# split into a training and testing set
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.25)
scaler = StandardScaler()
# Fit on training set only
# Apply transform to both the training set and the test set.
train_img = scaler.transform(X_train)
test_img = scaler.transform(X_test)

# Compute a PCA (eigenfaces) on the face dataset (treated as unlabelled dataset): 
# unsupervised feature extraction / dimensionality reduction
variance = 0.95
print("Extracting eigenfaces with %f variance from %d faces" % (variance, X_train.shape[0]))
Output:Extracting eigenfaces with 0.950000 variance from 966 faces
# PCA model
t0 = time()
pca = PCA(0.95, whiten=True).fit(X_train)
print("done in %0.3fs" % (time() - t0))
print("Projecting the input data on the eigenfaces orthonormal basis")


Output: done in 0.823s

# Implementing PCA transform
t0 = time()
X_train_pca = pca.transform(X_train)
X_test_pca = pca.transform(X_test)
print("done in %0.3fs" % (time() - t0))
Output: Projecting the input data on the eigenfaces orthonormal basisdone in 0.012s
eigenfaces = pca.components_.reshape(-1,h,w)
# print("Projecting the input data on the eigenfaces orthonormal basis")


(135, 50, 37)

# plot the gallery of the most significative eigenfaces
eigenface_titles = ["eigenface %d" % i for i in range(eigenfaces.shape[0])]
plot_gallery(eigenfaces, eigenface_titles, h, w)













# Train a SVM classification model
print("Fitting the classifier to the training set")
t0 = time()
clf = LogisticRegression(solver = 'lbfgs')
clf =, y_train)
print("done in %0.3fs" % (time() - t0))


Fitting the classifier to the training setdone in 0.068s



# Quantitative evaluation of the model quality on the test set
print("Predicting people's names on the test set")
t0 = time()
y_pred = clf.predict(X_test_pca)
print("done in %0.3fs" % (time() - t0))


Predicting people’s names on the test setdone in 0.002s

# Evaluate the accuracy
accuracy = (metrics.accuracy_score(y_test, y_pred))

Output: 0.7763975155279503

# Classification report, comments on f1 score
print(classification_report(y_test, y_pred, target_names=target_names))


precision    recall  f1-score   support      Ariel Sharon               0.65         0.77      0.71        22     Colin Powell               0.86         0.75      0.80        57  Donald Rumsfeld         0.62         0.80      0.70        25    George W Bush          0.84         0.82      0.83       135Gerhard Schroeder        0.79        0.77      0.78        30      Hugo Chavez             0.71        0.75      0.73        20       Tony Blair                 0.66        0.64      0.65        33         micro avg                 0.78       0.78       0.78       322        macro avg                0.73       0.76       0.74       322     weighted avg             0.78       0.78       0.78       322

# Evaluation of the confusion matrix 
confusion = (confusion_matrix(y_test, y_pred, labels=range(n_classes)))
# Visualisation
import seaborn as sns; sns.set()
ax = sns.heatmap(confusion, annot=True, fmt="d")







# Qualitative evaluation of the predictions using matplotlib
def plot_gallery(images, titles, h, w, n_row=3, n_col=4):
"""Helper function to plot a gallery of portraits"""
plt.figure(figsize=(1.8 * n_col, 2.4 * n_row))
plt.subplots_adjust(bottom=0, left=.01, right=.99, top=.90, hspace=.35)
for i in range(n_row * n_col):
plt.subplot(n_row, n_col, i + 1)
plt.imshow(images[i].reshape((h, w)),
plt.title(titles[i], size=12)
# plot the result of the prediction on a portion of the test set
def title(y_pred, y_test, target_names, i):
pred_name = target_names[y_pred[i]].rsplit(' ', 1)[-1]
true_name = target_names[y_test[i]].rsplit(' ', 1)[-1]
return 'predicted: %s\ntrue:      %s' % (pred_name, true_name)
prediction_titles = [title(y_pred, y_test, target_names, i)
for i in range(y_pred.shape[0])]
plot_gallery(X_test, prediction_titles, h, w)





An alumnus of the NIE-Institute Of Technology, Mysore, Prateek is an ardent Data Science enthusiast. He has been working at Acadgild as a Data Engineer for the past 3 years. He is a Subject-matter expert in the field of Big Data, Hadoop ecosystem, and Spark.

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