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Deep learning technologies are at the core of the current revolution in artificial intelligence for multimedia data analysis. The convergence of big annotated data and affordable GPU hardware has allowed the training of neural networks for data analysis tasks which had been addressed until now with hand-crafted features. Architectures such as convolutional neural networks, recurrent neural networks and Q-nets for reinforcement learning have shaped a brand new scenario in signal processing. This course will cover the basic principles and applications of deep learning to computer vision problems, such as image classification, object detection or text captioning.

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- 1. 1 DEEP LEARNING WORKSHOP Dublin City University 27-28 April 2017 Xavier Giro-i-Nieto xavier.giro@upc.edu Associate Professor Universitat Politecnica de Catalunya Technical University of Catalonia The Perceptron Day 1 Lecture 1 #InsightDL2017
- 2. 2 Acknowledgments
- 3. 3 Acknowledgments
- 4. 4 Outline 1. Supervised learning: Regression/Classification 2. Linear regression 3. Logistic regression 4. The Perceptron 5. Multi-class classification
- 5. 5 Machine Learning techniques We can categorize three types of learning procedures: 1. Supervised Learning: = ƒ( ) 2. Unsupervised Learning: ƒ( ) 3. Reinforcement Learning: = ƒ( ) We have a labeled dataset with pairs (x, y), e.g. classify a signal window as containing speech or not: x1 = [x(1), x(2), …, x(T)] y1 = “no” x2 = [x(T+1), …, x(2T)] y2 = “yes” x3 = [x(2T+1), …, x(3T)] y3 = “yes” ...
- 6. 6 Supervised Learning Build a function: = ƒ( ), ∈ ℝm , ∈ ℝⁿ Depending on the type of outcome we get… ● Regression: is continous (e.g. temperature samples = {19º, 23º, 22º}) ● Classification: is discrete (e.g. = {1, 2, 5, 2, 2}). ○ Beware! These are unordered categories, not numerically meaningful outputs: e.g. code[1] = “dog”, code[2] = “cat”, code[5] = “ostrich”, ...
- 7. 7 Regression motivation Text to Speech: Textual features → Spectrum of speech (many coefficients) TXT Designed feature extraction ft 1 ft 2 ft 3 Regression module s1 s2 s3 wavegen “Hand-crafted” features “Hand-crafted” features
- 8. 8 Classification motivation Automatic Speech Recognition: Acoustic features → Textual transcription (words) Designed feature extraction s1 s2 s3 Classifier “hola que tal” “Hand-crafted” features
- 9. 9 What “deep-models” means nowadays Learn the representations as well, not only the final mapping → end2end Learned extraction Classifier Model maps raw inputs to raw outputs, no intermediate blocks. End2end model “hola que tal”
- 10. 10 Linear Regression y = w · x + b Linear x Training a model means learning parameters w and b from data.
- 11. 11 Linear Regression y = w · x + b Linear x Input variable x is 1D in this example
- 12. 12 Linear Regression Input data can also be M-dimensional with vector x: y = wT · x + b = w1·x1 + w2·x2 + w3·x3 + … + wM·xM + b e.g. we want to predict the price of a house (y) based on: x1 = square-meters (sqm) x2,3 = location (lat, lon) x4 = year of construction (yoc) y = price = w1·(sqm) + w2·(lat) + w3·(lon) + w4·(yoc) + b
- 13. 13 Logistic Regression for Classification For classification, regressed values must be bounded between 0 and 1 to represent probabilities. The sigmoid function maps any input x between [0,1]: Sigmoid Linear regressor
- 14. 14 Setting a threshold (thr) at the output of the perceptron allows solving classification problems between two classes (binary): Logistic Regression for Classification
- 15. 15 The Perceptron (Neuron) The Perceptron can represent both linear & logistic regression: if ƒ(a)=a → linear if ƒ(a)=sigmoid(a) → logistic
- 16. 16 The output is derived by a sum of the weighted inputs plus a bias term. The Perceptron (Neuron)
- 17. 17 Weights and bias are the parameters that define the behavior (must be learned). The Perceptron (Neuron)
- 18. 18 The Perceptron is seen as an analogy to a biological neuron. Biological neurons fire an impulse once the sum of all inputs is over a threshold. The sigmoid emulates the thresholding behavior → act like a switch. Figure credit:Introduction to AI The Perceptron (Neuron)
- 19. 19 Binary classification with one neuron Setting a threshold (thr) at the output of the perceptron allows solving classification problems between two classes (binary): y > thr → class 1 (eg. YES) y < thr → class 2 (eg. NO)
- 20. 20 Binary classification with two neurons Probability estimations for each class can also be obtained by softmax normalization on the output of two neurons, one specialised for each class. J. Alammar, “A visual and interactive guide to the Basics of Neural Networks” (2016) Softmax normalization
- 21. 21 Binary classification with two neurons Normalization factor so that the sum of probabilities sum up to 1. J. Alammar, “A visual and interactive guide to the Basics of Neural Networks” (2016) Softmax normalization
- 22. 22 Three-class classification with 3 neurons TensorFlow, “MNIST for ML beginners”
- 23. 23 Three-class classification with 3 neurons TensorFlow, “MNIST for ML beginners”
- 24. 24 Three-class classification with 3 neurons TensorFlow, “MNIST for ML beginners”
- 25. 25 Multi-class classification Multiple classes can be predicted by putting many neurons in parallel, each processing its binary output out of N possible classes. 0.3 “dog” 0.08 “cat” 0.6 “whatever” raw pixels unrolled img Normalization factor, remember: we want a pdf at the output! → all output P’s sum up to 1. Softmax function
- 26. 26 Outline 1. Supervised learning: Regression/Classification 2. Linear regression 3. Logistic regression 4. The Perceptron 5. Multi-class classification
- 27. 27 Thanks ! Q&A ? https://imatge.upc.edu/web/people/xavier-giro @DocXavi /ProfessorXavi #InsightDL2017

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