| As one of the latest generation of display technologies,laser display has the advantages of large color gamut,high brightness,high efficiency,long lifetime,and healthy eye protection,which provides the audience with unique colorful "visual world".It has been listed in the key program of the medium and long term development of science and technology and novel strategic industrial layout.However,due to the high coherence of laser,the speckle phenomenon will seriously deteriorate the image quality.Laser speckle becomes a barrier for laser display products to enter the market on a large scale.Therefore,with the support of the national key research and development program,this dissertation presented a systematic study on the speckle issue in full-color laser display systems.The main research contents and results of the dissertation:1.For laser projection display systems,the speckle-reduction technology based on rotating ball lens was proposed,which solved the speckle issue in practical laser projection systems.This technology is based on active speckle reduction with angle diversity and has the advantages of low light loss,simple structure,and low manufacturing cost.Under the experimental conditions of different motor voltages,measuring distances,and laser driving currents,the ball lens device was proved to reduce speckle effectively.Finally,the ball lens was integrated into a complete projection system with the projection light pipe,and the composite speckle reduction was achieved.The green speckle of the display image was lower than the human speckle perception threshold.2.A color speckle measurement system based on human-eye visual characteristics was built,which could accurately measure the severity of speckle and evaluate the effect of speckle reduction.The traditional monochromatic speckle measurement was improved to color speckle measurement for a practical system.According to the requirements of the human-eye visual characteristics and color speckle calculations,the color-speckle measurement system based on human-eye visual characteristics was built and the key parameters related to color speckle were set properly.Then the system was calibrated for the highest and lowest speckle contrast,respectively,to ensure the measurement range and accuracy,which ensures the measurement results are similar to human eye observation.Finally,in the practical ball-lens system,the color-speckle reduction effect was measured and verified.The color speckle of the display image was lower than the human speckle perception threshold.3.The color-speckle assessment method in the 2D color diagram was studied and improved.With the experiments through the self-built color-speckle measurement system based on human eyes,the optimal color-speckle measurement and calculation method of practical projectors was presented.The formula for calculating color speckle with arbitrary irregular spectral distribution was derived based on the optical radiation power.Additionally,the formula was further extended to multi-primary laser display systems.The color speckle with different speckle contrast values and the number of primary colors were studied theoretically in the 2D uniform color diagram.In the experiments,a three-primary laser projector was used to analyze the two basic calculation schemes of color speckle with simulation and measurement.The experiments with color filters were compensated for the white point and the optimal method to measure color speckle was using monochromatic RGB images.Finally,aimed at the practical ball-lens system,the color-speckle reduction effect was verified in the 2D color diagram.4.In view of the color perception characteristics of human eyes,a novel colorspeckle assessment method in the 3D color space was proposed.With the experiments through the self-built color-speckle measurement system based on human eyes,the intuitive comparison of color speckle of different projectors with different luminance values was achieved.The formula of color speckle based on luminance was derived,and it was also further extended to multi-primary laser display systems.In the 3D Jzazbz color space,the color speckle of three-and multiprimary systems was simulated.Color-speckle characteristics and ellipsoid model were defined,which was used to compare the color speckle of projectors with different brightness simply and intuitively.In the experiments,three-and sixprimary laser projectors were used for measurement,and the color-speckle distributions of the two calculation schemes with simulation and measurement were consistent in the 3D color space.Finally,aimed at the practical ball-lens system,the color-speckle reduction effect was verified in the 3D color space.Highlights of the dissertation:1.The speckle-reduction technology based on rotating ball lens was proposed,which solved the speckle reduction problem in practical systems.This technology had the advantages of low light loss,high uniformity,simple structure and low manufacturing cost.The reduction principle of this technology was analyzed.The speckle reduction by this technology under different conditions was studied and proved to be effective.Combined with projection elements such as the light pipe,practical composite speckle reduction could be achieved and the color-speckle reduction effect was verified.The color speckle of the display image was lower than the human speckle perception threshold.2.A color-speckle measurement system based on human vision was built,which solved the speckle measurement problem in practical systems.The traditional monochromatic speckle measurement was improved to color speckle measurement for practical systems.According to human-eye visual characteristics,the key parameters related to color speckle in the system were discussed and optimized.The measurement system was calibrated with the highest and lowest speckle contrast values,respectively,which eliminated the grid noise of the measurement image pixels and ensured the measurement range and accuracy.The color-speckle pattern measured by the system was approximately the result observed by human eyes.3.The color-speckle assessment method in the 2D color diagram and 3D color space were studied and improved,which solved the speckle assessment problem in practical systems.The color speckle of practical light sources with arbitrary irregular spectral distribution was supplemented,and it was further extended to multi-primary display systems.With the experiments by a complete projector,the optimal method to measure color speckle was using monochromatic RGB images.Furthermore,a novel color-speckle assessment method based on the 3D Jzazbz color space was proposed.The color-speckle distribution characteristics of threeand multi-primary color systems were studied.A simplified model by colorspeckle ellipsoid was proposed to compare the color-speckle severity of different projectors,and it could also be used to evaluate the color-speckle reduction effect.In summary,a practical composite speckle reduction technique was proposed to solve the speckle problem of practical projectors.A color-speckle measurement system based on the human-eye visual characteristics was built and the corresponding assessment system,from monochrome to color,and from single speckle contrast to 2D or 3D colorimetric description,was established,which guides for the intuitive comparison of color speckle between different projection systems or projectors.Additionally,the assessment system is compatible with multi-primary laser display systems,which lays a foundation for the promotion of multi-primary laser displays and improvement for the international standards.In the future,laser display represents an important direction of the innovation of our national industry,which will greatly enhance the national core competitiveness in the field of display and realize the Chinese dream of watching their own laser TVs. |
