Styjun

Hello I am new to machine learning. I was on the process of training a VGG16 fine-tuned model.After the first epoch,the program stopped and gave this error:

Below is the code I used for the model:

# create a copy of a mobilenet model
import keras
vgg_model=keras.applications.vgg16.VGG16()

type(vgg_model)

vgg_model.summary()

from keras.models import Sequential
model = Sequential()
for layer in vgg_model.layers[:-1]:
 model.add(layer)

model.summary()

# CREATE THE MODEL ARCHITECTURE
from keras.layers import Dense, Activation, Dropout

model.add(Dropout(0.25))
model.add(Dense(7,activation='softmax'))

model.summary()

#Train the Model
# Define Top2 and Top3 Accuracy

from keras.metrics import categorical_accuracy, top_k_categorical_accuracy

def top_3_accuracy(y_true, y_pred):
 return top_k_categorical_accuracy(y_true, y_pred, k=3)

def top_2_accuracy(y_true, y_pred):
 return top_k_categorical_accuracy(y_true, y_pred, k=2)

from keras.optimizers import Adam
model.compile(Adam(lr=0.01), loss='categorical_crossentropy', 
 metrics=[categorical_accuracy, top_2_accuracy, top_3_accuracy])

# Get the labels that are associated with each index
print(valid_batches.class_indices)

# Add weights to try to make the model more sensitive to melanoma

class_weights=
 0: 1.0, # akiec
 1: 1.0, # bcc
 2: 1.0, # bkl
 3: 1.0, # df
 4: 3.0, # mel # Try to make the model more sensitive to Melanoma.
 5: 1.0, # nv
 6: 1.0, # vasc


filepath = "skin.h5"
checkpoint = ModelCheckpoint(filepath, monitor='val_top_3_accuracy', verbose=1, 
 save_best_only=True, mode='max')

reduce_lr = ReduceLROnPlateau(monitor='val_top_3_accuracy', factor=0.5, patience=2, 
 verbose=1, mode='max', min_lr=0.00001)


callbacks_list = [checkpoint, reduce_lr]

history = model.fit_generator(train_batches, steps_per_epoch=train_steps, 
 class_weight=class_weights,
 validation_data=valid_batches,
 validation_steps=val_steps,
 epochs=40, verbose=1,
 callbacks=callbacks_list)

I am trying to learn how to fine tune, train and use VGG16 model on image dataset. I was following this blog where he used mobileNet.

I was following this VGG16 tutorial to write the code for the model.

If anyone can help me fix this error or explain how and why it happened I would highly appreciate your help.

Thank you so much.

Dependencies:

• tensorflow 1.12.0


• tensorflow-gpu 1.12.0


• python 3.6.0


• keras 2.2.4

I had the same error when I used the ReduceLROnPlateau callback. Unless it's absolutely necessary, you can maybe omit its usage.