Study On Visual Health And Perceptual Characteristics For Laser Display

Laser display is mainly based on projection technology and takes the laser as the light source.The laser has excellent characteristics of monochromaticity,directionality,brightness,and long life.Therefore,laser display has the advantages of large screen,high brightness,wide color gamut,high contrast,and high resolution.As one of new display technologies,laser display has been widely used in many fields such as theater,engineering,education,business,and home.However,due to the laser's high energy and good convergence,laser display's optical radiation safety has attracted great attention from the public.Therefore,it is necessary to study the optical radiation safety of laser display.Besides,as a display product,people watch the screen of laser display for long time.So in addition to visual health problems caused by optical radiation,the perception of image contents needs to be considered.We conduct a series of research around the optical radiation safety and perceptual characteristics for laser display,and the main research contents and conclusions can be summarized into four aspects as listed below:(1)Based on the analyses of theories and standards relevant to optical radiation safety,evaluation requirements and evaluation methods of optical radiation safety for household ultra-short throw laser projection display systems have been put forward and developed as two Chinese national standards.Based on the analyses of relevant theories and standards for optical radiation safety,the blue light effect of the display and the optical radiation safety of various types of laser displays are studied.Suitable evaluation requirements and evaluation methods of optical radiation safety for household ultra-short throw laser projection display systems are especially put forward.The“evaluation requirements”and“evaluation methods”have been recognized by experts and peers at home and abroad and have been developed as GB/T 38246-2019“Evaluation requirements of optical radiation safety for household laser display systems”and GB/T 38248-2019“Evaluation methods of optical radiation safety for household laser display systems”,respectively.The two standards are used together and have supplemented and improved the application scope of the international standard IEC 60825series.Besides,the two standards and IEC 62471-5:2015 are well complemented each other but with different focuses.(2)The Helmholtz-Kohlrausch(H-K)phenomenon existing in the laser display is studied.The effects of color saturation and hue on perceived brightness of the laser display are revealed.Moreover,the effects of laser display with single color(blue)lasers or dual color(blue+red)lasers on perceived brightness are compared.The research results indicate that taking more than one kind of lasers as light source of laser display is helpful to expand the color gamut,improve the perceived brightness,and reduce the energy consumption.In this paper,the relations among perceived brightness,luminance,and chromaticity are investigated.Moreover,heterochromatic perceived brightness matching experiments are conducted for laser display.Based on two laser displays with single color lasers having the same parameters,the effects of color saturation and hue on perceived brightness are examined.Results show that when hue and luminance are the same respectively,higher color saturation corresponds to higher perceived brightness;furthermore,the effect of hue on the ratio of the system equivalent luminance to luminance(L_seq/L)of hue is as follows:blue>red>green.Based on two different laser displays with single color lasers,dual color lasers,the effects of different color gamut on perceived brightness are studied.Results indicate that when image and luminance are the same,wider color gamut of the display corresponds to higher perceived brightness;moreover,L_seq/L value of natural images is slightly lower than that of pure chromatic images with dominant hue.Nowadays,the color gamut becomes wider in laser displays with single-,dual-,and trinal-color lasers.The conversion efficacy of electric power to luminance in laser displays with dual and trinal color lasers increase by 3%or 24%,respectively,than that with single color lasers.Investigation results provide a theoretical basis for the optimization of laser displays with wider color gamut,lower power consumption,and higher perceived brightness.(3)Just noticeable differences(JNDs)of the four main image attributes that affect the image quality of laser display are measured and determined.Then the influential factors of the JNDs are analyzed.Further,the similarities and differences of the four attributes between laser display and liquid crystal display are compared.The display principles of laser display and flat panel display are different,and the color gamut of laser display is wider than that of flat panel display.These two types of displays will present different display effect with the same input images and bring different feelings to the audience.Herein,one to four just noticeable differences(JNDs)of the four attributes(white level,black level,color saturation,and contour rendering)for laser display are determined by visual perception experiments.Further,the influential factors concerning to the JNDs of the four attributes are analyzed.Results show that the JNDs of the four attributes are significantly correlated with the image contents.The JNDs of white level and black level are mainly influenced by luminance,the JNDs of color saturation are mainly affected by hue,and the JNDs of contour rendering are greatly affected by the texture features.Furthermore,the ratios of multiple just noticeable difference to one just noticeable difference of the four image attributes between the two displays are compared.The results denote that the ratios of contour rendering differ greatly,but the ratios of other three image attributes of the two displays are similar.The results provide a basis for further establishing an image quality model for laser display.(4)The model of laser display image quality relevant to image attributes is established,and the influential weights of the four image attributes to image quality are determined.Based on the image quality scoring experiment and statistical methods,the model between image quality and image attributes for laser display is built.Further,the influential weights of the four image attributes to image quality based on laser display and liquid crystal display are analyzed and compared.The results indicate that influential weights of laser display are as follows:contour rendering(41%)>color saturation(32%)>white level(19%)>black level(8%),and influential weights of liquid crystal display are as follows:contour rendering(34%)>white level(28%)>black level(20%)>color saturation(18%).The results are helpful for the improvement and optimization of laser display's image quality.