基于DMD的高动态范围成像光学系统设计

为了解决光电成像设备对空间实际场景观测时提出的高动态范围要求,设计了一种新型的像元级光强调制的高动态范围成像系统。系统由成像物镜、折叠反射镜、二次成像转置物镜组成,采用TI公司的数字微镜阵列（DMD）作为光强调制器件,通过光瞳匹配原则使两个系统完美衔接,并利用二次成像系统实现DMD单元与图像传感器的像素一一对应,设计结果显示:在像面的Nyquist频率处,全视场的MTF0.55,弥散圆的直径小于CMOS图像传感器的像素尺寸,并且畸变等像差也校正良好。该方法不仅可以提高图像传感器的可探测动态范围,还能够实时地探测到强弱目标,满足空间目标视景成像的要求。     

Analog multiplication at high frequencies with a high dynamic range

An analog multiplier has been constructed by means of field-effect transistors. The multiplier has a dynamic range higher than 80 dB and a frequency response that is flat to within 0.7 dB from 50 to 70 Mhz. This device would be very useful in applications where both inputs may vary by 40 dB or more.     

一种新型大动态范围CMOS图像传感器

提出了一种具有新型像素结构的大动态范围CMOS图像传感器,通过调整单个像素的积分时间来自适应不同的局部光照情况,从而有效提高动态范围。设计了一种低延时、低功耗、结构简单的新型pixel级电压比较器及基于可逆计数器的时间-电压编码电路。采用0.6μm DPDM标准数字CMOS工艺参数对大动态范围像素单元电路进行仿真,积分电容电压Vcint与光电流呈良好的线性关系,其动态范围可达126dB。在3.3V供电电压下,单个像元功耗为2.1μW。     

面向多用户的高动态范围视频动态范围可分级编码

提出了面向多用户的高动态范围(HDR,high dynamic range) 视频动态范围可分级编码方法,并利用视觉掩蔽特性抑制了噪声,提高了动态范围可 分级编码的效率。首先,考虑HDR视频感知特性,提出了动态范围可分级模型(DRSM,dynamic range scalable model),将不同动态范围级的HDR视频分解成为一个标准动态范围(SDR,s tandard dynamic range) 视频和多个残差信号帧(RSFs,residual signal frames)序列。然后,结合亮度掩蔽效应和 人眼感知特性,对 RSFs进行量化和滤波处理,滤除残差中的零散数据点,保留RSFs相邻动态范围级之间的整体 差异信息, 提高RSFs的编码效率。最后,在解码端重建得到SDR视频和各个动态范围级的HDR视频,以适 应多用 户端MDR显示设备。结果表明,所提出方法能在保持重建HDR视频的主观感知质量的同时降低 编码码率, 并在全帧内预测编码模式下,相同HDR-VDP-2.2和PSNR分值时,BD-rate (Bjntegaard D elta rate)平均节省了32.03%和31.28%,其编 码率失真性能有明显提升。     

Noise reduction in high dynamic range images

Multiple images with different exposures are used to produce a high dynamic range (HDR) image. Sometimes high-sensitivity setting is needed for capturing images in low light condition as in an indoor room. However, current digital cameras do not produce a high-quality HDR image when noise occurs in low light condition or high-sensitivity setting. In this paper, we propose a noise reduction method in generating HDR images using a set of low dynamic range (LDR) images with different exposures, where ghost artifacts are effectively removed by image registration and local motion information. In high-sensitivity setting, motion information is used in generating a HDR image. We analyze the characteristics of the proposed method and compare the performance of the proposed and existing HDR image generation methods, in which Reinhard et al.’s global tone mapping method is used for displaying the final HDR images. Experiments with several sets of test LDR images with different exposures show that the proposed method gives better performance than existing methods in terms of visual quality and computation time.     

Methods for improving the tone mapping for backward compatible high dynamic range image and video coding

Backward compatibility for high dynamic range image and video compression forms one of the essential requirements in the transition phase from low dynamic range (LDR) displays to high dynamic range (HDR) displays. In a recent work [1], the problems of tone mapping and HDR video coding are originally fused together in the same mathematical framework, and an optimized solution for tone mapping is achieved in terms of the mean square error (MSE) of the logarithm of luminance values. In this paper, we improve this pioneer study in three aspects by considering its three shortcomings. First, the proposed method [1] works over the logarithms of luminance values which are not uniform with respect to Human Visual System (HVS) sensitivity. We propose to use the perceptually uniform luminance values as an alternative for the optimization of tone mapping curve. Second, the proposed method [1] does not take the quality of the resulting tone mapped images into account during the formulation in contrary to the main goal of tone mapping research. We include the LDR image quality as a constraint to the optimization problem and develop a generic methodology to compromise the trade-off between HDR and LDR image qualities for coding. Third, the proposed method [1] simply applies a low-pass filter to the generated tone curves for video frames to avoid flickering during the adaptation of the method to the video. We instead include an HVS based flickering constraint to the optimization and derive a methodology to compromise the trade-off between the rate-distortion performance and flickering distortion. The superiority of the proposed methodologies is verified with experiments on HDR images and video sequences.     

AlGaAsSb-InGaAsSb HPTs with high optical gain and wide dynamic range

Novel heterojunction phototransistors based on AlGaAsSb-InGaAsSb material systems are fabricated and their characteristics are demonstrated. Responsivity of a phototransistor is measured with applied bias voltage at four different wavelengths. The maximum responsivity around 1400 A/W and minimum noise equivalent power of 1.83/spl times/10/sup -14/ W/Hz/sup 1/2/ from this phototransistor with bias of 4.0 V at a wavelength of 2.05 /spl mu/m were measured at 20/spl deg/C and -20/spl deg/C, respectively. Noise equivalent power of the phototransistor is considerably lower compared with commercially available InGaAs p-i-n photodiodes. Collector current measurements with applied incident power are performed for two phototransistors. Currents of 400 nA at low intensity of 0.425 /spl mu/W/cm/sup 2/ and of 30 mA at high intensity of 100 mW/cm/sup 2/ are determined. Collector current increases nearly by five orders of magnitude between these two input intensities. High and constant optical gain of 500 in the 0.46-nW to 40-/spl mu/W input power range is achieved, which demonstrates high dynamic range for such devices at these power levels.     

Visualization of high dynamic range images

A novel paradigm for information visualization in high dynamic range images is presented in this paper. These images, real or synthetic, have luminance with typical ranges many orders of magnitude higher than that of standard output/viewing devices, thereby requiring some processing for their visualization. In contrast with existent approaches, which compute a single image with reduced range, close in a given sense to the original data, we propose to look for a representative set of images. The goal is then to produce a minimal set of images capturing the information all over the high dynamic range data, while at the same time preserving a natural appearance for each one of the images in the set. A specific algorithm that achieves this goal is presented and tested on natural and synthetic data.     

Enabling stereoscopic high dynamic range video

Stereoscopic and high dynamic range (HDR) imaging are two methods that enhance video content by respectively improving depth perception and light representation. A large body of research has looked into each of these technologies independently, but very little work has attempted to combine them due to limitations in capture and display; HDR video capture (for a wide range of exposure values over 20 f-stops) is not yet commercially available and few prototype HDR video cameras exist. In this work we propose techniques which facilitate stereoscopic high dynamic range (SHDR) video capture by using an HDR and LDR camera pair. Three methods are proposed: one based on generating the missing HDR frame by warping the existing one using a disparity map; increasing the range of LDR video using a novel expansion operator; and a hybrid of the two where expansion is used for pixels within the LDR range and warping for the rest. Generated videos were compared to the ground truth SHDR video captured using two HDR video cameras. Results show little overall error and demonstrate that the hybrid method produces the least error of the presented methods.     

Intermodulation distortion in high dynamic range microwavefiber-optic links with linearized modulators

Linearization of integrated optic intensity modulators significantly reduces the two-tone intermodulation distortion. The resulting intermodulation distortion produced by these modulators then varies as the input power to the fifth-order link system, the overall intermodulation product is a combination of third-order and higher-order terms. The authors determine the dynamic range of a cascaded microwave network consisting of a preamplifier, a high-dynamic-range fiber-optic link with a highly linear modulator, and a postamplifier. An expression is found that relates the intermodulation power at the output to the relative suppression from the signal level. As an example, a hypothetical 10-GHz low-distortion fiber-optic link that has a dynamic range of 125 dB in a bandwidth of 1 Hz is cascaded with various preamplifiers, and it is shown that the dynamic range of the system is reduced by as much as 20 dB, depending on the third-order intercept of the amplifier     

CMOS selfbiased Euclidean distance computing circuit with high dynamic range

A CMOS analogue circuit is proposed that computes the Euclidean distance between two vectors whose coefficients are represented by currents. The circuit is selfbiased, requires only a small number of transistors, and offers good accuracy over a wide range of input values.<>     

Recovering high dynamic range by Multi-Exposure Retinex

The matter of generating high dynamic range (HDR) image from a number of differently exposed pictures arises to satisfy the needs of high-quality imaging and industrial applications. A number of HDR image generation algorithms have been proposed in the past. However, the HDR radiance map recovered by these classical methods cannot completely exclude the noisy pixels in the input images and thus are unable to produce the optimal result with highest possible SNR. In this paper we are going to introduce a new HDR generation algorithm based on the Multi-Exposure Retinex model deduced in this paper for HDR image composition. The luminance component L and the reflectance R are synthesized independently before being combined together. A novel R image composition method is introduced to help the composed result image reach the highest possible SNR. The method is tested on grey-level images in this paper, but it can be easily extended to the color-image version.     

红外焦平面成像系统动态范围自适应技术研究

针对目前一些红外焦平面阵列(IRFPA)成像系统动态范围较小的问题,分析比较了国内外在系统动态范围扩展方面的研究及其优缺点,介绍了通过自适应调节系统积分时间的工作方式来调整动态范围的方法。包括3个方面的内容：采用对获得图像进行特征判断的方法获取调整依据;结合LMS自适应滤波技术给出了调整算法;由于积分时间的变化会对系统非均匀性产生影响,结合两点校正法提出了一种简单可行的非均匀性问题的解决方案。最后,对整体方案进行了实验验证,通过实验证明了自适应动态范围调整方法的可行性,并获得了较好的效果,成像质量有明显提高。     

A tone mapping algorithm for acquisition of high dynamic range images using event-driven adaptive digital CMOS pixels

An algorithm for the tone mapping of high dynamic range (HDR) scenes in digital CMOS pixels has been developed. The algorithm performs a content-aware compression over HDR scenes, which produces a representation of several decades of acquired data while keeping the main contents in the scene using only 7-bits/pixel.     

Novel noise measurement setup with high dynamic range for optical receivers

A novel method is proposed, and verified experimentally, for wideband noise measurements with high dynamic range on optical receiver front ends. A synthetic white noise source, based on delayed selfhomodyne mixing, is calibrated with a weak shot noise source. The receiver noise is reconstructed from the calibrated synthetic noise source by ratio measurements.<>     

High frequency/high dynamic range CMOS VGA

A novel CMOS variable gain amplifier (VGA) with high frequency and high dynamic range is proposed. The VGA has a controllable gain range of -50 dB-+50 dB which can be controlled by adjusting the external voltage as well as an enhanced operating frequency range up to 200 MHz. It is fabricated using 0.35 μm CMOS technology and has a core area of 580×660 μm     

高动态范围(HDR)技术综述

高动态范围技术由于能够提供更多亮度和细节信息,近年来已逐渐成为国内外热点研究领域。文章主要从高动态范围成像、合成以及显示等方面论述、分析了高动态范围技术的研究现状,对主要研究算法总结并分析了其优缺点,分析了高动态范围技术的发展趋势,并给出了提高显示器动态范围的软件、硬件方案。     

Frequency selective limiters for high dynamic range microwavereceivers

A broadband frequency selective limiter (FSL) which provides over 14 dB of limiting across more than an octave bandwidth is described. The limiter is fabricated with epitaxially grown YIG (yttrium iron garnet) films in a stripline configuration and has a threshold power level of below 0 dBm. Individual limiter strips limit microwave signals in the 1-100-mW range across more than an octave of bandwidth. Multiple FSLs have been cascaded with amplifiers to allow compression of microwave signals with a power range of 60 dB into a range of less than 5 dB     

快速高能X射线光栅相衬成像

X射线光栅相衬成像对弱吸收物质成像能够获得较高的图像衬度,然而使用高分辨探测器,成像时间长。此外,受光栅工艺限制,成像能量通常在30 keV左右。文中基于投影成像原理,大大放宽了对光栅工艺的要求,提高了成像能量。同时,利用医用CT球管以及医用探测器,基于周步进扫描模式,实现了快速相衬CT成像。在国家同步辐射实验室搭建的成像系统上,完成了80 kV管电压（等效能量约48 keV）180 mA管电流,物体80 s曝光的二维和三维成像实验。针对实验结果,进一步探讨了提高密度分辨率的方法和途径。