An Introduction to Image Blending

How to use Gaussian and Laplacian image stacks to modify and combine images

TL;DR This article is an introduction to image blending techniques using Gaussian and Laplacian image stacks (expanded pyramids). The task of changing a background image provides an example of one use of this image processing method. A link to a Jupyter notebook with Python code is at the end of the article.

Image blending theory

The first step in image blending is to creates a “stack” of Gaussian lowpass filtered images from the original image. Each image in the stack is progressively blurrier as more higher spatial frequencies are removed using a Gaussian filter.

Gaussian filters (radial frequency response) (source: J. van Saders)

Gaussian stack example (source: J. van Saders)