Monogenic Signal (OpenCV Implementation)

This is a basic implementation of the monogenic signal for 2D images using the C++ language and the OpenCV library. As well the monogenic signal, several related quantities that can be derived from the monogenic signal, such as Feature Symmetry and Asymmetry, are also implemented.

The monogenic signal is an alternative way of representing an image, which has a number of advantages for further processing. For an introduction to the monogenic signal and derived features with references to the relevant scientific literature, please see this document (PDF).

Capabilities

Functions are provided to calculate the following quantities for 2D images:

• Monogenic Signal.
• Local Energy, Local Phase and Local Orientation to describe the local properties of image.
• Feature Symmetry and Asymmetry, respond to symmetric 'blobs' and boundaries with robustness to variable contrast.
• Oriented Feature Symmetry and Asymmetry, as above but also containing the polarity of the symmetry and the orientation of the boundaries.

This implementation was written with computational efficiency as a key objective, such that it can be used for video processing applications. It is designed to avoid redundant calculations when several quantities are desired from the same input image.

However, it is also straightforward and appropriate to use for calculating single quantities from still images.

Dependencies

• A C++ compiler supporting the C++11 standard (requires a relatively modern version of your compiler).
• The OpenCV library. Tested on version 4.2 but most fairly recent versions should be compatible. If you are using GNU/Linux, there will probably be a suitable packaged version in your distribution's repository.
• (Optional) If you use a C++ compiler supporting the OpenMP standard (includes most major compilers on major platforms including MSVC, g++ and clang) there may be a small speed boost due to parallelisation.

Instructions for Use

The implementation consists of a single C++ class (monogenicProcessor), defined in the src/monogenicProcessor.cpp and include/monogenic/monogenicProcessor.h files. To use the code in your project, you just need to include the .cpp file in the usual way, and add the repository's include/ directory in the include path.

There is an example programme showing how to use the class in the example/ directory. The comments in this file should demonstrate the basic usage.

Compiling and Running the Example

To compile the example on a GNU/Linux system, simply run the make command from the example/ directory. To run the example, then execute

$ ./monogenicTest video_file.avi

where video_file.avi is the name of a video file. This will then calculate the monogenic signal and feature symmetry and asymmetry images, and display then.

Author

Written by Christopher Bridge at the University of Oxford's Institute of Biomedical Engineering.