Machine Learning

A Gentle Introduction to Channels-First and Channels-Last Image Formats

Last Updated on September 12, 2019

Color images have height, width, and color channel dimensions.

When represented as three-dimensional arrays, the channel dimension for the image data is last by default, but may be moved to be the first dimension, often for performance-tuning reasons.

The use of these two “channel ordering formats” and preparing data to meet a specific preferred channel ordering can be confusing to beginners.

In this tutorial, you will discover channel ordering formats, how to prepare and manipulate image data to meet formats, and how to configure the Keras deep learning library for different channel orderings.

After completing this tutorial, you will know:

  • The three-dimensional array structure of images and the channels first and channels last array formats.
  • How to add a channels dimension and how to convert images between the channel formats.
  • How the Keras deep learning library manages a preferred channel ordering and how to change and query this preference.

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