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.
Highlights
Liquid Crystal Displays (LCDs) play a major role in providing improved image or video definition and colour reproduction in the flat panel display marketplace and increasingly for mobile devices
backlight local dimming (BLD) algorithms are fundamental for High Dynamic Range (HDR) displays as these tend to be significantly brighter than traditional displays
A similar method developed by Zhang et al [8] computed a correction term as the ratio of the difference of maximum and average luminance. Other methods, such as that introduced by Nam [9]; use both local and global brightness in order to find a better trade-off between enhancing local contrast and preserving the overall appearance of the LCD images, and a roll-off method was used to keep better image details in the high-level grey areas
Summary
Liquid Crystal Displays (LCDs) play a major role in providing improved image or video definition and colour reproduction in the flat panel display marketplace and increasingly for mobile devices. Cho and Kwon [7] used a correction term to adjust the average pixel intensity and considered the local difference between the maximum and average luminance They used a new method to reduce the clipping artefacts of LCD images displayed on the LCD panel by increasing the backlight luminance from the average luminance. A similar method developed by Zhang et al [8] computed a correction term as the ratio of the difference of maximum and average luminance Other methods, such as that introduced by Nam [9]; use both local and global brightness in order to find a better trade-off between enhancing local contrast and preserving the overall appearance of the LCD images, and a roll-off method was used to keep better image details in the high-level grey areas. The same settings as mentioned above were conducted using a SIM2 HDR47 display
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