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HomeArtificial IntelligenceUnderstanding the Design of a Convolutional Neural Community

Understanding the Design of a Convolutional Neural Community

Final Up to date on August 6, 2022

Convolutional neural networks have been discovered profitable in pc imaginative and prescient functions. Numerous community architectures are proposed, and they’re neither magical nor onerous to know.

On this tutorial, you’ll make sense of the operation of convolutional layers and their position in a bigger convolutional neural community.

After ending this tutorial, you’ll be taught:

  • How convolutional layers extract options from a picture
  • How completely different convolutional layers can stack as much as construct a neural community

Let’s get began.

Understanding the design of a convolutional neural community
Photograph by Kin Shing Lai. Some rights reserved.


This text is split into three sections; they’re:

  • An Instance Community
  • Exhibiting the Characteristic Maps
  • Impact of the Convolutional Layers

An Instance Community

The next is a program to do picture classification on the CIFAR-10 dataset:

This community ought to be capable of obtain round 70% accuracy in classification. The pictures are in 32×32 pixels in RGB shade. They’re in 10 completely different lessons, and the labels are integers from 0 to 9.

You possibly can print the community utilizing Keras’s abstract() operate:

On this community, the next shall be proven on the display screen:

It’s typical in a community for picture classification to be comprised of convolutional layers at an early stage, with dropout and pooling layers interleaved. Then, at a later stage, the output from convolutional layers is flattened and processed by some absolutely related layers.

Exhibiting the Characteristic Maps

Within the above community, there are two convolutional layers (Conv2D). The primary layer is outlined as follows:

This implies the convolutional layer may have a 3×3 kernel and apply on an enter picture of 32×32 pixels and three channels (the RGB colours). Due to this fact, the output of this layer shall be 32 channels.

With a view to make sense of the convolutional layer, you’ll be able to try its kernel. The variable mannequin holds the community, and you could find the kernel of the primary convolutional layer with the next:

This prints:

You possibly can inform that mannequin.layers[0] is the right layer by evaluating the title conv2d from the above output to the output of mannequin.abstract(). This layer has a kernel of the form (3, 3, 3, 32), that are the peak, width, enter channels, and output function maps, respectively.

Assume the kernel is a NumPy array okay. A convolutional layer will take its kernel okay[:, :, 0, n] (a 3×3 array) and apply on the primary channel of the picture. Then apply okay[:, :, 1, n] on the second channel of the picture, and so forth. Afterward, the results of the convolution on all of the channels is added as much as turn into the function map n of the output, the place n, on this case, will run from 0 to 31 for the 32 output function maps.

In Keras, you’ll be able to extract the output of every layer utilizing an extractor mannequin. Within the following, you’ll create a batch with one enter picture and ship it to the community. Then have a look at the function maps of the primary convolutional layer:

The above code will print the function maps like the next:

This corresponds to the next enter picture:

You possibly can see that they’re known as function maps as a result of they’re highlighting sure options from the enter picture. A function is recognized utilizing a small window (on this case, over a 3×3 pixels filter). The enter picture has three shade channels. Every channel has a unique filter utilized, and their outcomes are mixed for an output function.

You possibly can equally show the function map from the output of the second convolutional layer as follows:

This reveals the next:

From the above, you’ll be able to see that the options extracted are extra summary and fewer recognizable.

Impact of the Convolutional Layers

An important hyperparameter to a convolutional layer is the scale of the filter. Normally, it’s in a sq. form, and you’ll contemplate that as a window or receptive subject to take a look at the enter picture. Due to this fact, the upper decision of the picture, then you’ll be able to anticipate a bigger filter.

However, a filter too giant will blur the detailed options as a result of all pixels from the receptive subject by way of the filter shall be mixed into one pixel on the output function map. Due to this fact, there’s a trade-off for the suitable measurement of the filter.

Stacking two convolutional layers (with out every other layers in between) is equal to a single convolutional layer with a bigger filter. However a typical design to make use of these days is 2 layers with small filters stacked collectively slightly than one bigger with a bigger filter, as there are fewer parameters to coach.

The exception could be a convolutional layer with a 1×1 filter. That is often discovered as the start layer of a community. The aim of such a convolutional layer is to mix the enter channels into one slightly than reworking the pixels. Conceptually, this may convert a shade picture into grayscale, however often, you should use a number of methods of conversion to create extra enter channels than merely RGB for the community.

Additionally, word that within the above community, you might be utilizing Conv2D for a 2D filter. There’s additionally a Conv3D layer for a 3D filter. The distinction is whether or not you apply the filter individually for every channel or function map or contemplate the enter function maps stacked up as a 3D array and apply a single filter to rework it altogether. Normally, the previous is used as it’s extra affordable to think about no specific order during which the function maps needs to be stacked.

Additional Studying

This part gives extra assets on the subject if you’re seeking to go deeper.




On this submit, you may have seen how you can visualize the function maps from a convolutional neural community and the way it works to extract the function maps.

Particularly, you realized:

  • The construction of a typical convolutional neural community
  • What’s the impact of the filter measurement on a convolutional layer
  • What’s the impact of stacking convolutional layers in a community

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