very large value of loss in AlexNet - machine-learning

Question

Actually I am using AlexNet to classify my images in 2 groups , I am feeding images to the model in a batch of 60 images and the loss which I am getting after every batch is 6 to 7 digits large (for ex. 1428529.0) , here I am confused that why my loss is such a large value because on MNIST dataset the loss which I got was very small as compared to this. Can anyone explain me why I am getting such a large loss value.
Thanks in advance ;-)
Here is the code :-
import tensorflow as tf
import matplotlib.pyplot as plt
import numpy as np
import os
img_size = 227
num_channels = 1
img_flat_size = img_size * img_size
num_classes = 2
drop = 0.5
x = tf.placeholder(tf.float32,[None,img_flat_size])
y = tf.placeholder(tf.float32,[None,num_classes])
drop_p = tf.placeholder(tf.float32)
def new_weight(shape):
return tf.Variable(tf.random_normal(shape))
def new_bias(size):
return tf.Variable(tf.random_normal(size))
def new_conv(x,num_input_channels,filter_size,num_filters,stride,padd="SAME"):
shape = [filter_size,filter_size,num_input_channels,num_filters]
weight = new_weight(shape)
bias = new_bias([num_filters])
conv = tf.nn.conv2d(x,weight,strides=[1,stride,stride,1],padding=padd)
conv = tf.nn.bias_add(conv,bias)
return tf.nn.relu(conv)
def new_max_pool(x,k,stride):
max_pool = tf.nn.max_pool(x,ksize=[1,k,k,1],strides=[1,stride,stride,1],padding="VALID")
return max_pool
def flatten_layer(layer):
layer_shape = layer.get_shape()
num_features = layer_shape[1:4].num_elements()
flat_layer = tf.reshape(layer,[-1,num_features])
return flat_layer,num_features
def new_fc_layer(x,num_input,num_output):
weight = new_weight([num_input,num_output])
bias = new_bias([num_output])
fc_layer = tf.matmul(x,weight) + bias
return fc_layer
def lrn(x, radius, alpha, beta, bias=1.0):
"""Create a local response normalization layer."""
return tf.nn.local_response_normalization(x, depth_radius=radius,
alpha=alpha, beta=beta,
bias=bias)
def AlexNet(x,drop,img_size):
x = tf.reshape(x,shape=[-1,img_size,img_size,1])
conv1 = new_conv(x,num_channels,11,96,4,"VALID")
max_pool1 = new_max_pool(conv1,3,2)
norm1 = lrn(max_pool1, 2, 2e-05, 0.75)
conv2 = new_conv(norm1,96,5,256,1)
max_pool2 = new_max_pool(conv2,3,2)
norm2 = lrn(max_pool2, 2, 2e-05, 0.75)
conv3 = new_conv(norm2,256,3,384,1)
conv4 = new_conv(conv3,384,3,384,1)
conv5 = new_conv(conv4,384,3,256,1)
max_pool3 = new_max_pool(conv5,3,2)
layer , num_features = flatten_layer(max_pool3)
fc1 = new_fc_layer(layer,num_features,4096)
fc1 = tf.nn.relu(fc1)
fc1 = tf.nn.dropout(fc1,drop)
fc2 = new_fc_layer(fc1,4096,4096)
fc2 = tf.nn.relu(fc2)
fc2 = tf.nn.dropout(fc2,drop)
out = new_fc_layer(fc2,4096,2)
return out #, tf.nn.softmax(out)
def read_and_decode(tfrecords_file, batch_size):
'''read and decode tfrecord file, generate (image, label) batches
Args:
tfrecords_file: the directory of tfrecord file
batch_size: number of images in each batch
Returns:
image: 4D tensor - [batch_size, width, height, channel]
label: 1D tensor - [batch_size]
'''
# make an input queue from the tfrecord file
filename_queue = tf.train.string_input_producer([tfrecords_file])
reader = tf.TFRecordReader()
_, serialized_example = reader.read(filename_queue)
img_features = tf.parse_single_example(
serialized_example,
features={
'label': tf.FixedLenFeature([], tf.int64),
'image_raw': tf.FixedLenFeature([], tf.string),
})
image = tf.decode_raw(img_features['image_raw'], tf.uint8)
##########################################################
# you can put data augmentation here, I didn't use it
##########################################################
# all the images of notMNIST are 28*28, you need to change the image size if you use other dataset.
image = tf.reshape(image, [227, 227])
label = tf.cast(img_features['label'], tf.int32)
image_batch, label_batch = tf.train.batch([image, label],
batch_size= batch_size,
num_threads= 1,
capacity = 6000)
return tf.reshape(image_batch,[batch_size,227*227*1]), tf.reshape(label_batch, [batch_size])
pred = AlexNet(x,drop_p,img_size) #pred
loss = tf.reduce_mean(tf.nn.softmax_cross_entropy_with_logits(logits=pred,labels=y))
optimiser = tf.train.AdamOptimizer(learning_rate = 0.001).minimize(loss)
correct_pred = tf.equal(tf.argmax(pred,1),tf.argmax(y,1))
accuracy = tf.reduce_mean(tf.cast(correct_pred,tf.float32))
cost = tf.summary.scalar('loss',loss)
init = tf.global_variables_initializer()
with tf.Session() as sess:
sess.run(init)
merge_summary = tf.summary.merge_all()
summary_writer = tf.summary.FileWriter('./AlexNet',graph = tf.get_default_graph())
tf_record_file = 'train.tfrecords'
x_val ,y_val = read_and_decode(tf_record_file,20)
y_val = tf.one_hot(y_val,depth=2,on_value=1,off_value=0)
coord = tf.train.Coordinator()
threads = tf.train.start_queue_runners(coord=coord)
x_val = x_val.eval()
y_val = y_val.eval()
epoch = 2
for i in range(epoch):
_, summary= sess.run([optimiser,merge_summary],feed_dict={x:x_val,y:y_val,drop_p:drop})
summary_writer.add_summary(summary,i)
loss_a,accu = sess.run([loss,accuracy],feed_dict={x:x_val,y:y_val,drop_p:1.0})
print "Epoch "+str(i+1) +', Minibatch Loss = '+ \
"{:.6f}".format(loss_a) + ', Training Accuracy = '+ \
'{:.5f}'.format(accu)
print "Optimization Finished!"
tf_record_file1 = 'test.tfrecords'
x_v ,y_v = read_and_decode(tf_record_file1,10)
y_v = tf.one_hot(y_v,depth=2,on_value=1,off_value=0)
coord1 = tf.train.Coordinator()
threads1 = tf.train.start_queue_runners(coord=coord1)
x_v = sess.run(x_v)
y_v = sess.run(y_v)
print "Testing Accuracy : "
print sess.run(accuracy,feed_dict={x:x_v,y:y_v,drop_p:1.0})
coord.request_stop()
coord.join(threads)
coord1.request_stop()
coord1.join(threads1)

Answer 1

Take a look a what a confusion matrix is. It is a performance evaluator. In addition, you should compare your precision versus your recall. Precision is the accuracy of your positive predictions and recall is the ratio of positive instances that are correctly detected by the classifier. By combining both precision and recall, you get the F_1 score which is keep in evaluating the problems of your model.
I would suggest you pick up the text Hands-On Machine Learning with Scikit-Learn and TensorFlow. It is a truly comprehensive book and covers what I describe above in more detail.