Table of Contents

AlexNet (2012)
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AlexNet won the ImageNet competition in 2012 and ushered in the deep learning era. Here are its key innovations.

6 Key Innovations
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1. Deep Architecture
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5 Convolutional Layers + 3 Fully Connected Layers
Total: 60 million parameters

A groundbreaking network depth for its time.

2. ReLU Activation
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First major CNN to use ReLU (replacing tanh/sigmoid)

ActivationProblem
Sigmoid/TanhVanishing gradient
ReLUFast training, gradient preservation

3. Dropout Regularization
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50% Dropout applied to FC layers

A novel regularization technique for preventing overfitting.

4. GPU Training
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Trained on 2x GTX 580 GPUs in parallel

Hardware acceleration enabling large-scale network training.

5. Data Augmentation
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  • Image translations
  • Horizontal reflections
  • PCA color augmentation

Artificially expanding training data for better generalization.

6. Local Response Normalization (LRN)
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Normalization technique applied after ReLU.

Later replaced by Batch Normalization.

Architecture Summary
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LayerOutput SizeDetails
Input224×224×3RGB Image
Conv155×55×9611×11, stride 4
Conv227×27×2565×5
Conv313×13×3843×3
Conv413×13×3843×3
Conv513×13×2563×3
FC64096Dropout 50%
FC74096Dropout 50%
FC81000Softmax