Convolutional neural network in practice

Convolutional Neural Network in Practice

2016.11 [email protected]

Preliminaries

Buzz words nowadays

AIDeep

learning

Big dataMachine learning

Reinforcement Learning

???

Glossary of AI terms

From Roger Parloff, WHY DEEP LEARNING IS SUDDENLY CHANGING YOUR LIFE (Fortune, 2016).

Definitions

What is AI ?

“Artificial intelligence is that activity devoted to making machines intelligent, and intelligence is that quality that enables an entity to function appropriately and with foresight in its environment.”

Nils J. Nilsson, The Quest for Artificial Intelligence: A History of Ideas and Achievements (Cambridge, UK: Cambridge University Press, 2010).

“a computerized system that exhibits behavior that is commonly thought of as requiring intelligence”

Executive Office of the President National Science and Technology Council Committee on Technology: PREPARING FOR THE FUTURE OF ARTIFICIAL INTELLIGENCE (2016).

“any technique that enables computers to mimic human intelligence”

Roger Parloff, WHY DEEP LEARNING IS SUDDENLY CHANGING YOUR LIFE (Fortune, 2016).

My diagram of AI terms

Environment

Data, Rules, Feedbacks ...

Teaching

Self-Learning,Engineering

...

AI

y = f(x)

Catf F18f

Past, Present of AI

Decades-old technology

● Long long history. From 1940s …

● But,

○ Before Oct. 2012.

○ After Oct. 2012.

Venn diagram of AI terms

From Ian Goodfellow, Deep Learning (MIT press, 2016).

Performance Hierarchy

Data

Features

Algorithms

Flowcharts of AI


E2E(end-to-end)

Image recognition error rate

From https://www.nervanasys.com/deep-learning-and-the-need-for-unified-tools/

2012

Speech recognition error rate

2012

5 Tribes of AI researchers

Symbolists(Rule, Logic-based)

Connectionists(PDP assumption)

Bayesians EvolutionistsAnalogizers

vs.

Deep learning has had a long and rich history !

● 3 re-brandings.

○ Cybernetics ( 1940s ~ 1960s )

○ Artificial Neural Networks ( 1980s ~ 1990s)

○ Deep learning ( 2006 ~ )

Nothing new !

● Alexnet 2012

○ based on CNN ( LeCunn, 1989 )

● Alpha Go

○ based on Reinforcement learning and

MCTS ( Sutton, 1998 )

So, why now ?

● Computing Power

● Large labelled dataset

● Algorithm

Size of neural networks


Singularity or Transcendence ?

Depth is KING !

Brief history of deep learning


1st Boom 2nd Boom1st Winter



2nd Winter



3rd Boom

So, when 3rd winter ?

Nope !!!

● Features are mandatory in every AI problem.

● Deep learning is cheap learning! (Though someone can disprove the PDP assumptions, deep learning is the best practical tool in representation learning.)

Biz trends after Oct.2012.

● 4 big players leading this sector.

● Bloody hiring war.○ Along the lines of NFL football players.

Biz trend after Oct.2012.

● 2 leading research firms.

● 60+ startups

Biz trend after Oct.2012.

Future of AI

Venn diagram of ML

From David silver, Reinforcement learning (UCL cource on RL, 2015).

Unsupervised & Reinforcement Learning

● 2 leading research firms focus on:

○ Generative Models

○ Reinforcement Learning

Towards General Artificial Intelligence


Strong AI vs. Weak AIGeneral AI vs. Narrow AI

Generative Adversarial Network

Xi Chen et al, InfoGAN: Interpretable Representation Learning by Information Maximizing Generative Adversarial Nets ( 2016 )

Generative Adversarial Network

(From https://github.com/buriburisuri/supervised_infogan 2016)

https://github.com/buriburisuri/supervised_infogan

So what can we do with AI?

● Simply, it’s sophisticated software

writing software.

True personalization at scale!!!

Is AI really necessary ?

“a lot of S&P 500 CEOs wished they had started thinking sooner than they did about their Internet strategy. I think five years from now there will be a number of S&P 500 CEOs that will wish they’d started thinking earlier about their AI strategy.”

“AI is the new electricity, just as 100 years ago electricity transformed industry after industry, AI will now do the same.”

Andrew Ng., chief scientist at Baidu Research.

Conclusion

Computers have opened their eyes.

Convolution Neural Network

Convolution Neural Network

● Motivation

○ Sparse connectivity

■ smaller kernel size

○ Parameter sharing

■ shared kernel

○ Equivariant representation

■ convolution operation

Fully Connected(Dense) Neural Network

● Typical 3-layer fully connected neural network

Sparse connectivity vs.Dense connectivity

Sparse

Dense


Parameter sharing

(x1, s1) ~ (x5, s5) share a single

parameter


Equivariant representation

Convolution operation

satisfies equivariant property.

A bit of history

From : http://cs231n.stanford.edu/slides/winter1516_lecture6.pdf

https://github.com/vdumoulin/conv_arithmetic

http://cs231n.stanford.edu/slides/winter1516_lecture6.pdf


Basic module of 2D CNN

Pooling

● Average pooling = L1 pooling

● Max pooling = infinity norm pooling

Max Pooling

● To improve translation invariance.

Parameters of convolution

● Kernel size○ ( row, col, in_channel, out_channel)

● Padding

○ SAME, VALID, FULL

● Stride

○ if S > 1, use even kernel size F >

S * 2

1 dimensional convolution

pad(P=1) pad(P=1) pad(P=1)

stride(S=1)

kernel(F=3)

stride(S=2)

● ‘SAME’(or ‘HALF’) pad size = (F - 1) * S / 2● ‘VALID’ pad size = 0● ‘FULL’ pad size : not used nowadays


From : https://github.com/vdumoulin/conv_arithmetic

pad = ‘VALID’, F = 3, S = 1





pad = ‘SAME’, F = 3, S = 1





pad = ‘SAME’, F = 3, S = 2



Artifacts of strides

From : http://distill.pub/2016/deconv-checkerboard/

F = 3, S = 2


http://distill.pub/2016/deconv-checkerboard/



F = 4, S = 2





Pooling vs. Striding

● Same in the downsample aspect

● But, different in the location aspect

○ Location is lost in Pooling

○ Location is preserved in Striding

● Nowadays, striding is more popular

○ some kind of learnable pooling

Kernel initialization

● Random number between -1 and 1

○ Orthogonality ( I.I.D. )

○ Uniform or Gaussian random

● Scale is paramount.

○ Adjust such that out(activation)

values have mean 0 and variance 1

○ If you encounter NaN, that may be

because of ill scale.

Gabor Filter

Activation results

Initialization guide

● Xavier(or Glorot) initialization

○ http://jmlr.org/proceedings/papers/v9/glorot10a/glorot10a

.pdf

● He initialization

○ Good for RELU nonlinearity

○ https://arxiv.org/abs/1502.01852

● Use batch normalization if possible○ Immune to ill-scaled initialization

http://jmlr.org/proceedings/papers/v9/glorot10a/glorot10a.pdf



https://arxiv.org/abs/1502.01852


Image classification

Guide

● Start from robust baseline

○ 3 choices

■ VGG, Inception-v3, Resnet

● Smaller and deeper

● Towards getting rid of POOL and

final dense layer

● BN and skip connection are popular

VGG

● https://arxiv.org/abs/1409.1556

● VGG-16 is good start point.

○ apply BN if you train from scratch

● Image input : 224x224x3 ( -1 ~ 1 )

● Final outputs

○ conv5 : 7x7x512

○ fc2 : 4096

○ sm : 1000



VGG practical tricks

● If gray image

○ divide all feature nums by 2

● Replace FCs with fully convolutional

layers

○ variable size input image

○ training/evaluation augmentation

○ read 4~5 pages in this paper

Fully connected layer

● conv5 output : 7x7x512

● Fully connected layer

○ flatten : 1x25088

○ fc1 weight: 25088x4096

■ output : 1x4096

○ fc2 weight: 4096x4096

■ output : 1x4096

○ Fixed size image only

Fully convolutional layer● conv5 output : 7x7x512

● Fully convolutional layer

○ fc1 ← conv 7x7@4096

■ output : (row-6)x(col-6)x4096

○ fc2 ← conv 1x1@4096

■ output : (row-6)x(col-6)x4096

○ Global average pooling

■ output : 1x1x4096

○ Variable sized images

VGG Fully convolutional layer

From : https://github.com/buriburisuri/sugartensor/blob/master/sugartensor/sg_net.py


https://github.com/buriburisuri/sugartensor/blob/master/sugartensor/sg_net.py


Google Inception

Google Inception● https://arxiv.org/pdf/1512.00567.pdf

● Bottlenecked architecture.

○ 1x1 conv

○ latest version : v5 ( v3 is popular )

● Image input : 224x224x3 ( -1 ~ 1 )

● Final output

○ conv5 : 7x7x1024 ( or 832 )

○ fc2 : 1024

○ sm : 1000

https://arxiv.org/pdf/1512.00567.pdf


Batch Normalization● https://arxiv.org/pdf/1502.03167.pdf



Batch normalization

● Extremely powerful

○ Use everywhere possible

○ Absorb biases to BN’s shifts

Resnet

Resnet

● https://arxiv.org/pdf/1512.03385v1.pdf

● Residual block

○ skip connection + stride

○ bottleneck block

● Image input : 224x224x3 ( -1 ~ 1 )

● Final output

○ conv5 : 7x7x2048

○ fc2 : 1x1x2048 ( average pooling )

○ sm : 1000

https://arxiv.org/pdf/1512.03385v1.pdf


Resnet

● Very deep using skip connection○ Now, v2 - 1001 layer architecture

● Now, Resnet-152 v2 is the de-facto standard

Resnet

From : https://github.com/buriburisuri/sugartensor/blob/master/sugartensor/sg_net.py


https://github.com/buriburisuri/sugartensor/blob/master/sugartensor/sg_net.py


Summary

● Start from Resnet-50

● Use He’s initialization

● learning rate : 0.001 (with BN), 0.0001

(without BN)

● Use Adam ( should be alpha < beta ) optim

○ alpha=0.9, beta=0.999 (with easy training)

○ alpha=0.5, beta=0.95 (with hard training)

Summary

● Minimize hyper-parameter tuning or

architecture modification.

○ Deep learning is highly nonlinear and

count-intuitive

○ Grid or random search is expensive

Visualization

Kernel visualization

Feature visualization

t-SNE visualization

https://lvdmaaten.github.io/tsne/



Occlusion chart




Activation chart

http://yosinski.com/deepvishttps://www.youtube.com/watch?v=AgkfIQ4IGaM

http://yosinski.com/deepvis

http://yosinski.com/deepvis

https://www.youtube.com/watch?v=AgkfIQ4IGaM

https://www.youtube.com/watch?v=AgkfIQ4IGaM

CAM : Class Activation Map

http://cnnlocalization.csail.mit.edu/



Saliency Maps



Deconvolution approach



Augmentation

Augmentation

● 3 types of augmentation

○ Traing data augmentation

○ Evaluation augmentation

○ Label augmentation

● Augmentation is mandatory○ If you have really big data, then augment

data and increase model capacity

Training Augmentation● Random crop/scale

○ random L in range [256, 480]

○ Resize training image, short side = L

○ Sample random 224x224 patch

Training Augmentation● Random flip/rotate

● Color jitter

Training Augmentation● Random flip/rotate

● Color jitter

● Random occlude

Testing Augmentation● 10-crop testing ( VGG )

○ average(or max) scores

Testing Augmentation

● Multi-scale testing

○ Fully convolutional layer is mandatory

○ Random L in range [224, 640]

○ Resize training image such that short side

= L

○ Average(or max) scores

● Used in Resnet

Advanced Augmentation● Homography transform

○ https://arxiv.org/pdf/1606.03798v1.pdf



Advanced Augmentation● Elastic transform for medical image

○ http://users.loni.usc.edu/~thompson/MAP/warp.html

http://users.loni.usc.edu/~thompson/MAP/warp.html

http://users.loni.usc.edu/~thompson/MAP/warp.html

Augmentation in action

Other Augmentation● Be aggressive and creative!

Feature level Augmentation● Exploit equivariant property of CNN

○ Xu shen, “Transform-Invariant Convolutional Neural Networks for Image Classification and

Search”, 2016

○ Hyo-Eun Kim, “Semantic Noise Modeling for Better Representation Learning”, 2016



Image Localization

Localization and Detection



Classification + Localization



Simple recipe

CE loss

L2(MSE) loss

Joint-learning ( Multi-task learning )or

Separate learning



Regression head position



Multiple objects detection



R-CNN



Fast R-CNN



Faster R-CNN



Faster R-CNN

● https://arxiv.org/pdf/1506.01497.pdf

● de-facto standard





Segmentation

Semantic Segmentation



Naive recipe



Fast recipe



Multi-scale refinement



Recurrent refinement



Upsampling



Deconvolution



Skip connection

Olaf, U-Net: Convolutional Networks for Biomedical Image Segmentation, 2015

Instance Segmentation



R-CNN



Hypercolumns



Cascades



Deconvolution

● Learnable upsampling

○ resize * 2 + normal convolution

○ controversial names■ deconvolution, convolution transpose, upconvolution,

backward strided convolution, ½ strided convolution

○ Artifacts by strides and kernel sizes■ http://distill.pub/2016/deconv-checkerboard/

○ Restrict the freedom of architectures



Convolution transposed

From : https://arxiv.org/abs/1609.07009


½ strided(sub-pixel) convolution

From : https://arxiv.org/abs/1609.07009


ESPCN ( Efficient Sub-pixel CNN)

Periodic shuffle

Wenzhe, Real-Time Single Image and Video Super-Resolution Using and Efficient Sub-Pixel Convolutional Neural Network, 2016

L2 loss issue

Christian, Photo-Realistic Single Image Super-Resolution Using a Generative Adversarial Network, 2016

SRGAN

https://github.com/buriburisuri/SRGAN



Videos

ST-CNN



Long-Time ST-CNN



Summary

● Model temporal motion locally ( 3D CONV )

● Model temporal motion globally ( RNN )

● Hybrids of both

● IMHO, RNN will be replaced with 1D

convolution dilated (atrous convolution)

Unsupervised learning

Stacked Autoencoder

Stacked Autoencoder

● Blurry artifacts caused by L2 loss

Variational Autoencoder

● Generative model

● Blurry artifacts caused by L2 loss

Variational Autoencoder

● SAE with mean and variance regularizer

● Bayesian meets deep learning

Generative Model

● Find realistic generating function G(x) by deep learning !!!

y = G(x)

G : Generating functionx : Factors

y : Output data

GAN(Generative Adversarial Networks)

Ian. J. Fellow et al. Generative Adverserial Networks. 2014. ( https://arxiv.org/abs/1406.2661)

Discriminator

Generator

Adversarial Network

Results

( From Ian. J. Fellow et al. Generative Adverserial Networks. 2014. )

( From P. Kingma et al. Auto-Encoding Variational Bayes. 2013. )

Pitfalls of GAN

● Very difficult to train.

○ No guarantee to Nash Equilibrium.■ Tim Salimans et al, Improved Techniques for Training GANS, 2016.

■ Junbo Zhao et al, Energy-based Generative Adversarial Network,

2016.

● Cannot control generated data.

○ How can we condition generating

function G(x)?

InfoGAN

Xi Chen et al. InfoGAN: Interpretable Representation Learning by Information Maximizing Generative Adversarial Nets, 2016 ( https://arxiv.org/abs/1606.03657 )

● Add mutual Information regularizer for inducing latent codes to original GAN.


InfoGAN

Results

( From Xi Chen et al. InfoGAN: Interpretable Representation Learning by Information Maximizing Generative Adversarial Nets)

Results

Interpretable factors interfered on face dataset

Supervised InfoGAN

Results

(From https://github.com/buriburisuri/supervised_infogan)

AC-GAN● Augustus, “Conditional Image Synthesis With Auxiliary Classifier GANs”,

2016





Features of GAN

● Unsupervised

○ No labelled data used

● End-to-end

○ No human feature engineering

○ No prior nor assumption

● High fidelity

○ automatic highly non-linear pattern finding

⇒ Currently, SOTA in image generation.

Skipped topics

● Ensemble & Distillation

● Attention + RNN

● Object Tracking

● And so many ...

Computers have opened their eyes.

Thanks

Convolutional neural network in practice

Software

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