CNN Architecture
A typical CNN architecture alternates convolution and pooling layers, ending with fully connected layers for classification. The feature extraction part (conv+pool) learns patterns; the classification part makes predictions.
Typical Structure
Input → [Conv → Activation → Pooling] (repeat) → Flatten → Dense → OutputEach conv layer learns increasingly complex features. Early conv: edges, corners. Middle conv: textures, patterns. Late conv: object parts, shapes.Example: Simple CNN for MNIST
model = Sequential([
Conv2D(32, (3,3), activation='relu', input_shape=(28,28,1)),
MaxPooling2D((2,2)),
Conv2D(64, (3,3), activation='relu'),
MaxPooling2D((2,2)),
Conv2D(64, (3,3), activation='relu'),
Flatten(),
Dense(64, activation='relu'),
Dense(10, activation='softmax')
])Depth (Number of Filters)
Common pattern: double the number of filters after each pooling. Example: 32 → 64 → 128. This compensates for reduced spatial size.
Receptive Field
The region of the input that influences a neuron. Deeper layers have larger receptive fields, allowing them to capture larger patterns.
Two Minute Drill
- Typical CNN: conv+pool blocks → flatten → dense.
- Depth (filters) often increases after each pooling.
- Early layers detect simple patterns; deeper layers detect complex objects.
- Receptive field grows with depth.
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