Laser displays commonly utilize spatial light modulators (SLM) as imaging devices, but the contrast ratio is limited by uniform illumination and the diffraction properties of SLM, which hinder the realization of high dynamic range (HDR) within a single frame. We investigate the fundamental diffraction properties of a phase light modulator (PLM) using the blazed grating model, explore its capability to steer beams, and evaluate its uniformity as a light field modulator. By employing PLM to modulate various light field distributions and conducting contrast ratio tests in laser display systems, we examine the illumination characteristics of PLM. We specifically select a representative light field distribution to assess the contrast ratio and analyze how altering the light field distribution through PLM affects it. Our findings reveal that reducing the proportion of individual spot size relative to the entire image area enhances the contrast ratio when there is a single spot area present in the modulated light field; conversely, increasing their number decreases the contrast ratio when multiple spots are present in the modulated image. By integrating PLM with a digital micromirror device (DMD), we have validated the feasibility of manipulating light field illumination in display systems, resulting in a remarkable improvement of over 300 times in contrast ratio and achieving HDR of projected images. Through utilization of the central light spot image to confirm its smaller proportion within the entire image, we can enhance the contrast ratio by more than 100 times and peak brightness by over 70 times. These findings demonstrate the viability of employing this approach to achieve HDR in laser displays.
Image enhancement plays an important role in the field of underwater vision. Numerous underwater image enhancement algorithms have been proposed in the last few years, which have achieved some good results in processing specific underwater images. However, the effectiveness of these algorithms to cope with different underwater environments remains uncertain. To address this issue, we propose a water body classification label based on scattering characteristics and construct a dataset with a large number of photos of experiments in different water conditions. Meanwhile, based on different types of water bodies we also trained a network model which has thirteen classifications. Using this dataset, we study comprehensively these underwater image enhancement algorithms qualitatively and quantitatively and match each type of underwater image with an optimal underwater image enhancement algorithm. An underwater image enhancement algorithm based on deep-learning water pre-classification is then proposed. This adapted algorithm is applied to process real underwater images captured by the underwater robot and obtains good processing results. It also contributes to further research on underwater image enhancement.
Underwater 3D reconstruction has important applications in Marine science, underwater archaeology and resource survey. As a structured light system based on active illumination, fringe projection contour method has been widely used in industrial measurement and manufacturing. However, there are still some shortcomings in the application of turbid water environment, such as the refraction of multi-layer media and the scattering and absorption caused by turbid water, resulting in a large area of information loss or reconstruction failure. This paper aims to study the improvement and application of fringe projection profilometry based on structured light projection technology in turbid water. A calibration scheme suitable for underwater system is proposed to compensate the influence of multi-layer medium refraction on the system. In order to verify the feasibility and effectiveness of this method, a reconstruction experiment was carried out in a pool in muddy water. The reconstruction results are analyzed based on the effective point cloud number, measurement error and Hausdorff distance. The results show that even under high turbidity conditions, the number of reconstructed point clouds has reached millions, and the accuracy can be maintained at the millimeter level, which reflects that the proposed method has potential practical value in the field of high-density and high-precision three-dimensional reconstruction in turbid water environment.
KEYWORDS: Diffraction, High dynamic range imaging, Blazed gratings, Modulation, Digital micromirror devices, Micromirrors, Light sources and illumination
Texas Instruments has developed a Phase Light Modulator (PLM) based on Digital Light Processing (DLP) System, which alters the distribution of the light field. This paper explores the fundamental diffraction properties of PLM using the blazed grating model, investigates its capability to steer beams and tests its uniformity as a light field modulator. We selected a typical light field distribution to test the contrast ratio and examined how changing the light field distribution through PLM affects contrast ratio. When there is a single spot area exists in the modulated light field, decreasing the proportion of the individual spot to the entire image area, increases the contrast ratio; When there are multiple spots in the modulated image, increasing their number, decreases the contrast ratio. The feasibility of arbitrarily manipulating light field illumination for display system applications is verified by combining PLM with Digital Micromirror Device (DMD), leading to improved contrast ratios and better realization of High Dynamic Range (HDR) in projected images.
Texas Instruments has developed a phase light modulator (PLM) based on Micro-Electromechanical System (MEMS). This modulator offers several excellent advantages, including high refresh rate, compact optical path, and high optical efficiency, making it well-suited for applications in laser displays. In this paper, we divide the PLM into three regions and illuminate them with corresponding color laser light. The diffracted image is eventually reproduced and superimposed at the image plane in order to obtain a colorful display. We measured the display indicators such as inherent resolution, coincidence error, contrast ratio, uniformity, optical efficiency and diffraction efficiency of this methodology. The advantages of this methodology lie in its compact optical path and excellent optical efficiency. This work enhances the development of single PLM for color laser display applications in field sequence, including holography and volume display.
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