Low complexity in-loop skin tone detection for ROI coding in the HEVC encoder

Perceptual video coding with rate control is a technique commonly used to improve the perceptual video quality without compromising on the video bit rate. Region of Interest (ROI) detection has traditionally been done by a dedicated software or hardware block which provides the video encoder the coordinates of the regions whose perceptual video quality needs to be higher than non-ROI regions. This paper introduces a low complexity human skin color based ROI detection technique in-loop with the HEVC encoder which classifies a coding unit as skin or not. The proposed method utilizes the HEVC encoder tools of spatial predictive encoding, variable coding unit block sizes and motion vectors generated during motion estimation to optimize skin tone detection in Intra and Inter predicted frames. The in-loop classification was found to improve the detection precision per operation per pixel by 4x compared to other low cost skin classifiers.