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Convolutional layer

As explained in Machine Learning Algorithms in Depth

A convolutional layer is a neural-network layer that applies learned convolution kernels to an input representation.

A convolutional layer applies learned filters, or kernels, across an input representation to produce feature maps. For an image of width W, height H, and C channels, a two-dimensional convolution evaluates a dot product at each possible kernel position. Convolutional layers reduce parameter counts and help preserve translation invariance. section 10.2

A convolutional operation proceeds by:

  • Sliding a kernel across the input matrix. section 10.2
  • Computing a dot product between the kernel and the input values at each position. section 10.2
  • Collecting the resulting scalar values into a feature map. section 10.2
  • Applying nonlinear activation functions between stacked convolutional layers. section 10.2

From handwritten digits to sequence similarity

A LeNet-style MNIST classifier stacks convolution, ReLU, and max-pooling operations, increases the number of filters, flattens the final feature map, and finishes with a dense softmax classifier. For question-pair similarity, Conv1D and max-pooling process each embedded question branch before concatenation and dense classification. section 10.2.1 section 10.3.2

(10.8)
figure

Use the convolution figure to inspect how kernel positions generate feature-map values. section 10.2

How Machine Learning Algorithms in Depth covers it

How deep it goes
Defines sliding kernels, dot products, feature maps, stacking, and activation placement, but does not derive gradient formulas.
Examples
Demonstrates 2D image convolution in LeNet for MNIST and 1D convolution in a multi-input question-similarity model.
What you can do after
Builds CNNs with Conv2D or Conv1D, pooling, nonlinearities, and downstream classification layers in Keras/TensorFlow.
How it connects
Connects convolutional layers with pooling, ReLU, dense layers, softmax classifiers, feature maps, and translation invariance.

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