Method Of Using Local Dimming To Improve Dynamic Contrast Of Liquid Cristal Display

Liquid Cristal Display(LCD)is the most popular flat display product in the world.HDR(High Dynamic Range)has become a hot filed of technology in recent years,the display of product with this feature has better display quality with deeper black and brighter white.Liquid Crystal cannot emit light itself and only can change the transmissivity of light,so that there has to be a backlight source behind it.There is little room for improvement under the current technical conditions for the contrast radio of LCD,but by adding dynamic controlled backlight,there is still improvement on the contrast ratio of the final display image.LED(Light Emitting Diode)is the most mainstream backlight source now due to its advantage of high power efficiency,long lifetime and fast response speed,and it also enables the local dynamic control of backlight.According to the placement of LED,the backlight system could be divided into two categories of side-emitting type & direct-emitting type.The side-emit type usually places the LED on one or both sides of the LCD module and use light guide plate and other optical structure to improve the uniformity of the light of the whole display area.The side-emit ting type has its advantage of slim and modern outlook and low cost,and it has become the most commonly used structure for LCD TV product with size between 40 ~ 60 inch.In this thesis,the backlight module of a side side-emitting LCD display is divided into 16 individually controlled channels and dynamic backlight control algorithm is added to the system to increase the dynamic range of the display.The test sample has increase its dynamic range from 1000:1 to 100,000:1.In this thesis discusses the design of hardware system,software system and the evaluation method in both object and subject method.In the hardware system,we solve the problem of power unbalance due to deviation of voltage drop on different LED string.In software system,we add spatial filter and time domain filter to improve the display quality and solve image abnormal in some certain condition.At the meantime we designed a temperature control system that could estimate the temperature of each channel and help prevent LED reaching a super high temperature that could shorten the lifetime of LED.Finally,we evaluate the performance of the sample display and got a significant improvement on dynamic contrast and achieve major design target.