How to reduce light leakage and clipping in local‐dimming liquid‐crystal displays

Abstract

Abstract— In conventional LCDs, the backlight is set to maximum luminance regardless of the image. For dark scenes, this approach causes light leakage and power waste. Especially, light leakage in dark scenes degrades the contrast ratio of LCDs; to circumvent this problem, local‐dimming systems have been proposed. In these systems, the LED backlight is divided into several local blocks and the backlight luminance of each local block is controlled individually, and pixel values are adjusted simultaneously according to the luminance profile of the dimmed backlight. In this paper, a method of determining the LED backlight luminance of each local block depending on the image is proposed; this method significantly improves the image quality of LCDs. First, we introduce methods of quantifying light‐leakage at dark gray levels and clipping at bright gray levels. Then, the proposed method to determine the dimming duty, which controls the LED backlight luminance by compromising between these two measures, was derived. The proposed algorithm preserves the original image with little clipping distortion and effectively reduces light leakage.

Modeling Power-Constrained Optimal Backlight Dimming for Color Displays

“…It should be noted that the model described in this Section is specified in the physical domain, i.e., physical luminance, , is assumed in (1)- (8). In this work, we shall approximate with the Gamma function, i.e., (10) The inverse response is simply given by (11) In this work, for simplicity, we approximate the HVS response to luminance with (10) and…”

“…Kang et al [9] presented an algorithm where multi-histograms are used to analyze the pixel distribution for the RGB components of the input image and set the backlight to limit the occurrence of clipping. The algorithm proposed by Kim et al [10] calculates the backlight segment intensity by analyzing the neighboring segments and by comparing leakage and clipping measures. Albrecht et al [2] introduced a clipper-free algorithm which minimizes the power consumption under this constraint.…”

“…2. We have used gradient descent (18) to calculate the perceptual optima at Full HD resolution; the cost function is as in (15) but with and in the perceptual domain (approximated with (10)) and with all the elements of set to 1. The starting solution was generated with the Min-Max approach (16) minimizing the same norm and with perception-based error weighting enabled at a downscaling factor of 5.…”

“…More complex algorithms use features like the global [8] or local histogram [9]. The backlight level in each segment can be improved by considering the neighboring ones [10]. To calculate the backlight more accurately, other algorithms use some level of knowledge of the point spreading function (PSF, also called light spread function [8]), that is how the light spreads from a point source on the diffuser plate [2]- [4].…”

A laser current control algorithm to avoid color distortion in laser projection displays

“…A fixed working current is needed to achieve stable primary light ratio and image quality performance. One of the important advantages of solid‐state light sources, such as laser and LED, compared with traditional gaseous light sources is that their luminous can be adjusted in real time, so that ultra‐high dynamic contrast and energy saving can be achieved . However, when dynamically dimming the display light source, problems such as brightness saturation and color shift are often encountered.…”