OpenCV Meanshift Tracking HSV

Question

I was wondering why in OpenCV examples when it comes to meanshift tracking, only Hue channel is used.

In https://docs.opencv.org/4.x/d7/d00/tutorial_meanshift.html such line of code implies what I wrote:

roi_hist = cv.calcHist([hsv_roi],[0],mask,[180],[0,180])

I understand main idea to convert RGB color space to HSV, but I do not get why only selecting Hue is enough. I know that roi_hist is later used to create back projection, but I also know that it is possible to create 2-D roi_hist by selecting also Saturation.

What it depends on? Should I expected that adding Saturation will improve my tracking results? I want to perform face tracking so I am looking for skin color.

Thanks in advance for help.

Answer 1

The OpenCV tutorial you linked references the paper that introduces CAMSHIFT. The CAMSHIFT algorithm was designed to track human faces. On page three, the paper states:

Except for albinos, humans are all the same color (hue). Dark- skinned people simply have greater flesh color saturation than light-skinned people, and this is separated out in the HSV color system and ignored in our flesh-tracking color model.

The use of the H in HSV allows for a single channel tracker that works for most human faces.