Seminar5


Week6

In this part, we'll load a pre-trained network and play with it.


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from __future__ import print_function
from sys import version_info

import matplotlib.pyplot as plt
import numpy as np
import os
import scipy
import theano
import theano.tensor as T
import lasagne

try:
    import cPickle as pickle
except ImportError:
    import pickle

%matplotlib inline

from scipy.misc import imread, imsave, imresize
from lasagne.utils import floatX

Model Zoo (4 pts)

Lasagne has a plethora of pre-training netrworks in the model zoo

  • Even more models within the community (neighbor repos, PRs, etc.)

We'll start by picking VGG16 and deploying it in our notebook.

Warning! VGG16 network requires around 3GB of memory to predict event for single-image batch. If you don't have that luxury, try binder or azure notebooks.


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!wget https://s3.amazonaws.com/lasagne/recipes/pretrained/imagenet/vgg16.pkl -O weights.pkl

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# copyright: see http://www.robots.ox.ac.uk/~vgg/research/very_deep/


from lasagne.layers import InputLayer
from lasagne.layers import DenseLayer
from lasagne.layers import NonlinearityLayer
from lasagne.layers import DropoutLayer
from lasagne.layers import Pool2DLayer as PoolLayer
from lasagne.layers import Conv2DLayer as ConvLayer
from lasagne.nonlinearities import softmax


def build_model():
    <paste network architecture here>
    return net

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#classes' names are stored here
classes = pickle.load(open('classes.pkl', 'rb'))
#for example, 10th class is ostrich:
print(classes[9])

You have to implement two functions in the cell below.

Preprocess function should take the image with shape (w, h, 3) and transform it into a tensor with shape (1, 3, 224, 224). Without this transformation, our net won't be able to digest input image. Additionally, your preprocessing function have to rearrange channels RGB -> BGR and subtract mean values from every channel.


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MEAN_VALUES = np.array([104, 117, 123])
IMAGE_W = 224

def preprocess(img):
    img = <convert RGB to BGR>
    
    img = <substract mean>
    
    #convert from [w,h,3 to 1,3,w,h]
    img = np.transpose(img, (2, 0, 1))[None]
    return floatX(img)

def deprocess(img):
    img = img.reshape(img.shape[1:]).transpose((1, 2, 0))
    for i in range(3):
        img[:,:, i] += MEAN_VALUES[i]
    return img[:, :, :: -1].astype(np.uint8)

img = (np.random.rand(IMAGE_W, IMAGE_W, 3) * 256).astype(np.uint8)

print(np.linalg.norm(deprocess(preprocess(img)) - img))

If your implementation is correct, the number above will be small, because deprocess function is the inverse of preprocess function

Deploy the network


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net = build_model()

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with open('weights.pkl', 'rb') as f:
    if version_info.major == 2:
        weights = pickle.load(f)
    elif version_info.major == 3:
        weights = pickle.load(f, encoding='latin1')
    
<load weights into the network>

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input_image = T.tensor4('input')
output = lasagne.layers.get_output(net[<which layer>], input_image)

prob = theano.function([input_image], output)

Sanity check

Let's make sure our network actually works.

To do so, we'll feed it with some example images.


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img = imread('sample_images/albatross.jpg')
plt.imshow(img)
plt.show()

p = prob(preprocess(img))

labels = p.ravel().argsort()[-1:-6:-1]
print('top-5 classes are:')
for l in labels:
    print('%3f\t%s' % (p.ravel()[l], classes[l].split(',')[0]))
Ouch!

Try running network 2-3 times. If output changes, then we've probably done something wrong.

Figure out, what's the problem with the network.

hint there are two such 'problematic' layers in vgg16. They're all near the end.

You can make network deterministic by giving it such flag in the lasagne.layers.get_output function above.

Fun opportunity

ImageNet does not contain any human classes, so if you feed the network with some human photo, it will most likely hallucinate something which is closest to your image.

Try feeding the network with something peculiar: your avatar, Donald Trump, Victor Lempitsky or anyone.

Grand-quest: Dogs Vs Cats (6 pts)

Your main objective

  • In this seminar your goal is to fine-tune a pre-trained model to distinguish between the two rivaling animals
  • The first step is to just reuse some network layer as features

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!wget https://www.dropbox.com/s/d61lupw909hc785/dogs_vs_cats.train.zip?dl=1 -O data.zip
!unzip data.zip
#you may need to adjust paths in the next section, depending on your OS

for starters

  • Train sklearn model, evaluate validation accuracy (should be >80%

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#extract features from images
from tqdm import tqdm
from scipy.misc import imresize

X = []
Y = []

#this may be a tedious process. If so, store the results in some pickle and re-use them.
for fname in tqdm(os.listdir('train/')):
    y = fname.startswith("cat")
    img = imread("train/"+fname)
    img = preprocess(imresize(img,(IMAGE_W,IMAGE_W)))
    features = <preprocess the image into features)
    Y.append(y)
    X.append(features)

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X = np.concatenate(X) #stack all [1xfeature] matrices into one. 
assert X.ndim==2
#WARNING! the concatenate works for [1xN] matrices. If you have other format, stack them yourself.

#crop if we ended prematurely
Y = Y[:len(X)]

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from sklearn.cross_validation import train_test_split

<split data either here or by cross-validation>

load our dakka


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from sklearn.ensemble import RandomForestClassifier,ExtraTreesClassifier,GradientBoostingClassifier,AdaBoostClassifier
from sklearn.linear_model import LogisticRegression, RidgeClassifier
from sklearn.svm import SVC
from sklearn.tree import DecisionTreeClassifier

Main quest

  • Get the score improved!

No methods are illegal: ensembling, data augmentation, NN hacks. Just don't let test data slip into training.

The main requirement is that you implement the NN fine-tuning recipe:

Split the raw image data

  • please do train/validation/test instead of just train/test
  • reasonable but not optimal split is 20k/2.5k/2.5k or 15k/5k/5k ### Choose which vgg layers are you going to use
  • Anything but for prob is okay
  • Do not forget that vgg16 uses dropout ### Build a few layers on top of chosen "neck" layers.
  • a good idea is to just stack more layers inside the same network
  • alternative: stack on top of get_output ### Train the newly added layers for some iterations
  • you can selectively train some weights by only sending them to your optimizer
    • lasagne.updates.mysupermegaoptimizer(loss, only_those_weights_i_wanna_train)
  • selecting all weights from the head but not below the neck:
    • all_params = lasagne.layers.get_all_params(new_output_layer_or_layers,trainable=True)
    • old_params= lasagne.layers.get_all_params(neck_layers,trainable=True)
    • new_params = [w for w in all_params if w not in old_params]
  • it's cruicial to monitor the network performance at this and following steps ### Fine-tune the network body
  • probably a good idea to SAVE your new network weights now 'cuz it's easy to mess things up.
  • Moreover, saving weights periodically is a no-nonsense idea
  • even more cruicial to monitor validation performance
  • main network body may need a separate, much lower learning rate
    • since updates are dictionaries, one can just compute union
    • updates = {}
    • updates.update(lasagne.updates.how_i_optimize_old_weights())
    • updates.update(lasagne.updates.how_i_optimize_old_weights())
    • make sure they do not have overlapping keys. Otherwise, earlier one will be forgotten.
    • assert len(updates) == len(old_updates) + len(new_updates) ### PROFIT!!!
  • Evaluate the final score
  • Submit to kaggle

Some ways to get bonus points

  • explore other networks from the model zoo
  • play with architecture
  • 85%/90%/93%/95%/97% kaggle score (screen pls).
  • data augmentation, prediction-time data augmentation
  • use any more advanced fine-tuning technique you know/read anywhere
  • ml hacks that benefit the final score

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print("I can do it!")

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