Learning OpenCV 4 Computer Vision with Python 3 - Third Edition

Calculating and back-projecting color histograms

To calculate a color histogram, OpenCV provides a function called cv2.calcHist. To apply a histogram as a lookup table, OpenCV provides another function called cv2.calcBackProject. The latter operation is known as histogram back-projection, and it transforms a given image into a probability map based on a given histogram. Let's first visualize the output of these two functions, and then examine their parameters.

A histogram can use any color model, such as blue-green-red (BGR), hue-saturation-value (HSV), or grayscale. (For an introduction to color models, refer to Chapter 3, Processing Images with OpenCV, specifically the Converting images between different color models section.) For our samples, ...