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.     

基于虚拟曝光图像的立体高动态范围图像合成算法

本文提出基于多视点多曝光图像的立体高动态范围图像合成算法。首 先,考虑多视点多曝光 图像以及相机响应函数曲线的特性,提出一种虚拟曝光图像绘制算法,将不同曝光的图像绘 制到同一视点;然后, 为了使绘制曝光图像保留更多细节和结构,需要对绘制虚拟曝光图像进行空洞填补及边缘修 复,故引入了边缘差值 掩膜图,对图像边缘信息进行校正平滑处理;最后利用绘制的虚拟曝光图像合成立体高动态 范围图像。实验结果表 明,获得的绘制曝光图像与参考曝光视点图像之间的结构相似性高达0.99以上,且合成的 高动态范围图像质量高。     

一种宽动态范围下的红外图像局部细节增强算法

针对红外图像在宽动态范围下压缩到窄动态范围时带来的图像细节显示模糊、暗处细节丢失以及对比度偏低等问题,提出了一种基于引导滤波分层的红外图像细节自适应增强算法。对背景层利用优化的CLAHE算法来进行压缩,对细节层利用脉冲噪声的多尺度检测并结合韦伯定理的方法进行压缩;解决前述的弱细节模糊以及暗部细节丢失问题。综合主、客观实验结果表明,相对于映射类、分层增强类以及Retinex和集成学习类增强算法,本文所提算法在背景层对比度和光照强度优化、细节层噪声抑制和弱细节增强上取得优异效果;在信息熵、PSNR和SSIM三种客观评测指标下综合效果最佳;处理速度达到150 f/s。在保证实时性的同时,不仅提高了图像的整体对比度,还突出了图像的局部细节,适用于宽温度范围下复杂环境的应用。     

Gradient field multi-exposure images fusion for high dynamic range image visualization

This paper presents a novel method for fusing multi-exposure images into a low dynamic range (LDR) image that is suitable for display and visualization but it contains details in the high dynamic range (HDR) counterpart. Fused gradient field is derived from the structure tensor of inputs based on multi-dimensional Riemannian geometry with a Euclidean metric assumed. Afterwards, a new method is proposed for modifying the gradient field iteratively with twice average filtering and nonlinearly compressing in multi-scales. These modification operations are all done at the finest resolution. The result is obtained through solving a Poisson equation then linearly stretching to the common range. Experimental results demonstrate the efficiency and effectiveness of this method.     

Ghost detection and removal for high dynamic range images: Recent advances

High dynamic range (HDR) image generation and display technologies are becoming increasingly popular in various applications. A standard and commonly used approach to obtain an HDR image is the multiple exposures' fusion technique which consists of combining multiple images of the same scene with varying exposure times. However, if the scene is not static during the sequence acquisition, moving objects manifest themselves as ghosting artefacts in the final HDR image. Detecting and removing ghosting artefacts is an important issue for automatically generating HDR images of dynamic scenes. The aim of this paper is to provide an up-to-date review of the recently proposed methods for ghost-free HDR image generation. Moreover, a classification and comparison of the reviewed methods is reported to serve as a useful guide for future research on this topic.     

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。     

Quasi-continuous waveform design for dynamic range reduction

A study of quasi-continuous waveform and its performance in detection is presented, taking into consideration eclipsing loss and free- space decay. A genetic algorithm is then used to optimise the waveform and lower the dynamic range of the matched filtering output. The resulting waveform with high duty cycle and minimal loss at maximal range maintains good detection performance along the whole operating range of the radar.     

激光雷达距离像噪声抑制及方法评价

针对激光成像雷达距离像距离反常噪声的噪声抑 制问题,提出了一种改进环圈滤波(IDF)算法并进行了评价。首先,根据 激光雷达距离像噪声的构成,建立了一般化的距离像噪声仿真模型,模型中包含了地面、目 标和细小结构等成分,可模拟 距离反常、失落信息和内部噪声等噪声干扰;其次,提出了一种IDF噪声抑制算法的一般形 式,利用仿真模型对中 值滤波(MF)、IDF等噪声抑制算法进行了分析,对计算结果从整体、非异常 值和细小结构等多个方面, 评价了算法的噪声抑制能力和保护目标细节信息能力;最后,采用实测距离像对算法进行了 验证。研究结果表明,利用建立 的距离像噪声仿真模型,可以有效地评价不同噪声抑制算法的 能力;同时,利用IDF可 以根据目标特性选取校正系数,在满足算法对保护目标细节信息能力要求的前提下,提高噪 声抑制能力。     

Reversible data hiding scheme for high dynamic range images based on multiple prediction error expansion

For sensitive areas that even the slight distortion in images is not tolerated, we propose a prediction error expansion-based reversible data hiding algorithm which can embed reversible watermark in high dynamic range (HDR) image with low distortion. On the one hand, considering unique floating-point storage format and perceptual characteristics of HDR image, the multiple carriers are generated with low distortion and various characteristics to improve the embedding capacity. On the other hand, multi-model predictor and multi-level embedding strength are adopted adaptively to realize multi-level reversible HDR image information hiding based on prediction error expansion. The experimental results show that the proposed algorithm has good invisibility by making full use of HDR image characteristics. Meanwhile, the multiple strategies of multiple carriers, multi-model predictor and multi-level embedding strength, which further improve the embedding capacity and security of the algorithm, can meet the needs of sensitive areas such as medical processing, judicial authentication, and so on.     

Noise reduction of VQ encoded images through anti-gray coding

Noise reduction of VQ encoded images is achieved through the proposed anti-gray coding (AGC) and noise detection and correction scheme. In AGC, binary indices are assigned to the codevector in such a way that the 1-b neighbors of a code vector are as far apart as possible. To detect the channel errors, we first classify an image into uniform and edge regions. Then we propose a mask to detect the channel errors based on the image classification (uniform or edge region) and the characteristics of AGC. We also mathematically derive a criterion for error detection based on the image classification. Once error indices are detected, the recovered indices can be easily chosen from a “candidate set” by minimizing the gray-level transition across the block boundaries in a VQ encoded image. Simulation results show that the proposed technique provides detection results with smaller than 0.1% probability of error and more than 86.3% probability of detection at a random bit error rate of 0.1%, while the undetected errors are invisible. In addition, the proposed detection and correction techniques improve the image quality (compared with that encoded by AGC) by 3.9 dB     

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.     

Noise reduction using multiscale bilateral decomposition for digital color images

In this paper, we propose a noise reduction algorithm for digital color images using a nonlinear image decomposition approach. Most existing noise reduction methods do not adequately consider spatial correlation of color noise in digital color images. Color noise components in color images captured by digital cameras are observed as irregular grains with various sizes and shapes, which are spatially randomly distributed. We use a modified multiscale bilateral decomposition to effectively separate signal and mixed-type noise components, in which a noisy input image is decomposed into a base layer and several detail layers. A base layer contains strong edges, and most of noise components are contained in detail layers. Noise components in detail layers are reduced by an adaptive thresholding function. We obtain a denoised image by combining a base layer and noise-reduced detail layers. Experimental results show the effectiveness of the proposed algorithm, in terms of both the peak signal-to-noise ratio and visual quality.     

Advantages of multiscale product filters for dynamic range compression in images

A multiscale product filter (MSPF) structure is proposed for use in digital image enhancement. The objective for this type of image processing is to mitigate the effect of uneven illumination on perceived image quality, a process known as dynamic range compression (DRC). The properties of the MSPF for DRC are investigated, a theoretical model is presented, and this model is used to predict the performance of the filter under step changes in illumination such as those caused by shadows. The advantage of the MSPF is that it provides a relatively rapid response for transitions from shadow regions to well-lit regions. This property is verified using random Mondrian textures with simulated illumination changes. The estimated illumination profile is compared with that used to generate the synthetic image using the Pearson's correlation coefficient. The improved performance of the MSPF is also confirmed by the mitigation of shadow artefacts in real images     

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.     

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.     

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.     

Noise reduction for magnetic resonance images via adaptive multiscale products thresholding

Edge-preserving denoising is of great interest in medical image processing. This paper presents a wavelet-based multiscale products thresholding scheme for noise suppression of magnetic resonance images. A Canny edge detector-like dyadic wavelet transform is employed. This results in the significant features in images evolving with high magnitude across wavelet scales, while noise decays rapidly. To exploit the wavelet interscale dependencies we multiply the adjacent wavelet subbands to enhance edge structures while weakening noise. In the multiscale products, edges can be effectively distinguished from noise. Thereafter, an adaptive threshold is calculated and imposed on the products, instead of on the wavelet coefficients, to identify important features. Experiments show that the proposed scheme better suppresses noise and preserves edges than other wavelet-thresholding denoising methods.     

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。     

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。