HDR And WCG Display Technologies Based On Local Dimming Algorithms

High dynamic range(HDR)technologies are capable of capturing,storing and displaying a much wider dynamic range of luminance compared to low dynamic range(LDR)technologies.HDR imaging can significantly improve visual experience and has been used in photography,gaming,films,medical and industrial imaging.However,because of the limitation of dynamic range and colour gamut,conventional liquid crystal displays(LCD)cannot show image contents with high dynamic range and wide colour gamut.To solve this problem,this thesis conducted research on local dimming algorithms to improve the dynamic range of the display.Furthermore,this thesis extended local dimming algorithms with white backlighting to colour local dimming algorithms with multi-primary colour backlighting to widen the colour gamut.The main contributions of this thesis are summarized as follows:(1)An objective evaluation methodology for local dimming algorithms was proposed.This work explored the relationship between LCD images and power consumption when using HDR displays.A comprehensive subjective and objective evaluation experiments for five backlight local dimming algorithms were conducted.In the objective experiment,a novel objective evaluation methodology was proposed based on the display model.Subsequently,some typical evaluation metrics,such as pu PSNR,pu SSIM,HDR-VDP,were used to evaluate different local dimming algorithms.Finally,Pearson correlation tests and Spearman rank correlation tests were used to analyse the ranking results of subjective evaluation and objective evaluation.The results show that the proposed objective evaluation results correspond to the subjective results.(2)A deep local dimming algorithm was proposed based on HDR displays.To obtain the optimal backlight values and improve the LCD image quality,this work used the UNet to predict backlight values.In this network,a luminance adjustment variable was introduced to keep the balance between power saving ratio and LCD image quality during the training process.The results show that the proposed algorithm can improve the processing speed and the power saving ratio as well as the LCD image quality compared with the other local dimming algorithms.(3)A multi-primary colour local dimming algorithm was proposed based on one HDR-WCG display.To improve dynamic range and extend color gamut for LCD displays,this work developed one HDR-WCG display and analysed the colour gamut of the proposed display system based on the LCD model.In addition,a colour local dimming algorithm was proposed based on the HDR-WCG display system.The results show that the colour gamut coverage of this display system is 45.65%.The peak luminance is around 1200(8(9/8)~2 and the minimum luminance is less than 0.02(8(9/8)~2.Compared with the standard colour gamut,the colour gamut coverage of this system has increased by about 12%and the dynamic range meets the requirement of the HDR display.