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Strided convolution

As explained in Deep Learning with R, Third Edition

A strided convolution is a convolution that moves its kernel by more than one input location at a time to reduce spatial resolution.

A strided convolution moves its kernel by more than one input location at a time, downsampling a feature map while continuing to extract features. This is useful when spatial location matters: unlike 2 × 2 max pooling, it preserves more information about where features occur. section 11.3.2

Compressing an image for segmentation

An image-segmentation model can use strided Conv2D layers to reduce spatial dimensions three times, producing a compact feature map such as (25, 25, 256). Conv2DTranspose layers then expand that representation back to the input size so the model can predict a class for every pixel. In R/Keras, a typical encoder uses `conv(64, 3, strides = 2)`, followed by further strided convolutions, while the decoder uses corresponding transpose convolutions. section 11.3.2

The same choice appears in object detection. A YOLO model uses a strided convolution after a ResNet backbone to reduce feature maps from (14, 14, 2048) to (6, 6, 512), making the representation manageable for dense prediction layers. section 12.2.2

How Deep Learning with R, Third Edition covers it

How deep it goes
Explains the practical role and architecture placement, but does not derive convolution-stride mechanics mathematically.
Examples
Demonstrates strided Conv2D in an encoder-decoder segmentation model and a YOLO detection head.
What it assumes
Assumes familiarity with convolutional layers and feature maps while motivating the choice from image-location requirements.
What you can do after
Apply it via Keras Conv2D layers to downsample feature maps in location-sensitive vision models.
How it connects
Connects strided convolution to convolutional neural networks, max pooling, image segmentation, object detection, and transposed convolution.

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This explainer was generated by Manning's knowledge graph from the text of Deep Learning with R, Third Edition. The section links point to the parts of the book it draws on.