Subjective and Objective Evaluation of Local Dimming Algorithms for HDR Images

Abstract

In order to enhance viewing experiences, a number of backlight local dimming (BLD) algorithms have been developed to improve the image contrast ratio and provide power efficiency for modern displays. In order to evaluate which BLD algorithm performs best for HDR images rendering on dual-panel displays, this paper presents a comprehensive subjective and objective evaluation conducted with five BLD algorithms across a number of scenes. The subjective evaluation (N = 24) required participants to rank each BLD generated image based on which they thought was the most natural looking. The objective evaluation was undertaken via the use of a novel methodology to generate the images per BLD for comparison against the ground truth High Dynamic Range (HDR) image. Resulting images were compared with the ground truth using qualitative methods namely: HDR-VDP, puPSNR, puSSIM and puVIFP. The power-saving rate of each method was also calculated. The results demonstrate a strong correlation between objective and subjective evaluation. Furthermore, results show that BLD algorithms that consider the luminance balance between backlight and LCD images perform better than straightforward BLD methods.

Keywords

• Local dimming algorithms
• HDR displays
• quality assessment
• HDR image processing