Exercise 12.3 - Solution¶
Discriminative localization (CAM)¶
In this exercise we will create class activation maps (CAMs) for predictions made by a model trained to classify magentic phases (see Exercise 7_1).
- Pick out two correctly and two wrongly classified images classified with a convolutional network.
- Look at Exercise 8.1 to extract weights and feature maps from the trained network model.
- Create and plot the class activation maps and compare them with the images in order to see which regions lead to the prediction.
In [3]:
from tensorflow import keras
import numpy as np
callbacks = keras.callbacks
layers = keras.layers
print("keras", keras.__version__)
Load and prepare dataset¶
See https://doi.org/10.1038/nphys4035 for more information
In [4]:
import gdown
url = "https://drive.google.com/u/0/uc?export=download&confirm=HgGH&id=1Ihxt1hb3Kyv0IrjHlsYb9x9QY7l7n2Sl"
output = 'ising_data.npz'
gdown.download(url, output, quiet=True)
f = np.load(output)
n_train = 20000
x_train, x_test = f["C"][:n_train], f["C"][n_train:]
T_train, T_test = f["T"][:n_train], f["T"][n_train:]
Tc = 2.27
y_train = np.zeros_like(T_train)
y_train[T_train > Tc] = 1
y_train = keras.utils.to_categorical(y_train, 2)
y_test = np.zeros_like(T_test)
y_test[T_test > Tc] = 1
y_test = keras.utils.to_categorical(y_test, 2)
Plot data¶
In [5]:
import matplotlib.pyplot as plt
for i,j in enumerate(np.random.choice(n_train, 6)):
plt.subplot(2,3,i+1)
image = x_train[j]
plot = plt.imshow(image)
plt.title("T: %.2f" % T_train[j])
plt.tight_layout()
plt.show()
Definition of the model¶
Define a CNN for discriminative localization. Note that the CNN must use GlobalAveragePooling2D after the convolutional part and must not feature more than a single fully-connected layer as output.
In [6]:
model = keras.models.Sequential()
model.add(layers.InputLayer(input_shape=(32, 32)))
model.add(layers.Reshape((32, 32,1)))
model.add(layers.Convolution2D(16, (3, 3), padding='same', activation='relu'))
model.add(layers.Convolution2D(16, (3, 3), padding='same', activation='relu'))
model.add(layers.MaxPooling2D((2, 2)))
model.add(layers.Convolution2D(32, (3, 3), padding='same', activation='relu'))
model.add(layers.Convolution2D(32, (3, 3), padding='same', activation='relu'))
model.add(layers.GlobalAveragePooling2D())
model.add(layers.Dropout(0.25))
model.add(layers.Dense(2, activation='softmax'))
model.summary()
prepare model for training¶
In [7]:
model.compile(
loss='binary_crossentropy',
optimizer=keras.optimizers.Adam(0.001),
metrics=['accuracy'])
In [8]:
results = model.fit(x_train, y_train,
batch_size=64,
epochs=50,
verbose=2,
validation_split=0.1,
callbacks=[
callbacks.EarlyStopping(patience=5, verbose=1),
callbacks.ReduceLROnPlateau(factor=0.67, patience=2, verbose=1)]
)
Evaluate training¶
In [9]:
plt.figure(1, (12, 4))
plt.subplot(1, 2, 1)
plt.plot(results.history['loss'])
plt.plot(results.history['val_loss'])
plt.ylabel('loss')
plt.xlabel('epoch')
plt.legend(['train', 'val'], loc='upper right')
Out[9]:
In [10]:
plt.figure(1, (12, 4))
plt.subplot(1, 2, 1)
plt.plot(results.history['accuracy'])
plt.plot(results.history['val_accuracy'])
plt.ylabel('accuracy')
plt.xlabel('epoch')
plt.legend(['train', 'val'], loc='upper right')
Out[10]:
Create class activation maps¶
Extract the activations of the last convolutional layer.
In [11]:
conv = model.layers[-4]
conv_func = keras.models.Model(model.inputs, conv.output)
A = conv_func.predict(x_test)
print(A.shape)
Create the class activation maps by omitting the global average pooling operation and applying the weights of the single classification layer to the extracted activations.
In [12]:
W, b = model.layers[-1].get_weights()
M = np.einsum('ixyz,zc->ixyc', A, W) + b
In [13]:
y_pred = model.predict(x_test, verbose=1)
y_pred = np.argmax(y_pred, axis=-1).round()
y_true = np.argmax(y_test, axis=-1).round()
In [14]:
idx_correct = np.where(y_true == y_pred)[0]
In [15]:
idx_wrong = np.where(y_true != y_pred)[0]
Plot the class activation maps for examples just below and above the critical temperature¶
In [16]:
def plot_CAM(M, x_test, idx):
X = x_test[idx,...] # the image itself
M1 = M[idx,..., 0] # activation map for T < Tc
M2 = M[idx,..., 1] # activation map for T > Tc
fig, (ax1, ax2) = plt.subplots(1, 2, sharey=True, figsize=(10, 4))
fig.subplots_adjust(right=0.8, wspace=0.05)
# plot image (twice)
ax1.imshow(X, cmap=plt.cm.gray, extent=(0, 32, 0, 32))
ax2.imshow(X, cmap=plt.cm.gray, extent=(0, 32, 0, 32))
# plot overlay of class activations, perform upsampling by bilinear interpolation
kwargs = dict(cmap=plt.cm.magma, extent=(0, 32, 0, 32),
interpolation='bilinear', alpha=0.7)
_1 = ax1.imshow(M1, **kwargs)
_2 = ax2.imshow(M2, **kwargs)
cbar = fig.colorbar(_1, cax=fig.add_axes([0.82, 0.1, 0.02, 0.8]))
cbar.set_label('Class activation')
ax1.set_title('Ferromagnetic CAM (T < Tc)')
ax2.set_title('Paramagnetic CAM (T > Tc)')
plt.show()
Plot correctly classified sample
In [17]:
plot_CAM(M, x_test, np.random.choice(idx_correct, 1)[0])
Plot wrongly classified sample
In [18]:
plot_CAM(M, x_test, np.random.choice(idx_wrong, 1)[0])
