Spatially varying image based lighting using HDR-video

Illumination is one of the key components in the creation of realistic renderings of scenes containing virtual objects. In this paper, we present a set of novel algorithms and data structures for visualization, processing and rendering with real world lighting conditions captured using High Dynamic Range (HDR) video. The presented algorithms enable rapid construction of general and editable representations of the lighting environment, as well as extraction and fitting of sampled reflectance to parametric BRDF models. For efficient representation and rendering of the sampled lighting environment function, we consider an adaptive (2D/4D) data structure for storage of light field data on proxy geometry describing the scene. To demonstrate the usefulness of the algorithms, they are presented in the context of a fully integrated framework for spatially varying image based lighting. We show reconstructions of example scenes and resulting production quality renderings of virtual furniture with spatially varying real world illumination including occlusions.     

基于图像的光照

基于图像的光照技术是利用现实世界的光照图像来照明现实的或计算机生成的场景及物体的一种方法。介绍了基于图像光照的基本方法和步骤，在LightWave 3D图形软件中建立三维物体模型，加入高动态范围图像作为场景照明环境，通过光通量与高动态范围图像的结合，获得了逼真的光照及环境映射图像。     

Image quality evaluation for OLED-based smart-phone displays at various lighting conditions

The image quality of three organic light-emitting diode (OLED) based smart-phone displays was assessed at three levels of ambient lighting conditions corresponding to the darkroom, indoor and outdoor environment, respectively. Seven perceptual attributes, i.e., naturalness, colorfulness, brightness, contrast, sharpness, preference, and overall image quality (IQ), were evaluated in both standard dynamic range (SDR) and high dynamic range (HDR) mode via psychophysical experiments by rank order method, while readability was assessed only in SDR mode and gradation was investigated only in HDR mode. The experimental results demonstrate that, besides the color gamut, the tone reproduction curve is also an important factor affecting the colorfulness of mobile display in the two modes. Higher peak luminance would not mean better performance on brightness and contrast for HDR images, which is opposite to SDR mode. Further analysis of variance (ANOVA) indicates that the ranking results of all perceptual attributes are not significantly affected by the ambient lighting levels in both SDR and HDR modes.     

基于Retinex理论的多曝光图像融合算法

多曝光图像融合技术是将一组场景相同但曝光程度不同的图像序列直接融合成为一幅含有更多场景细节信息的高质量图像。针对现有算法局部对比度差和色彩失真的问题，结合Retinex理论模型提出了一种新的多曝光图像融合算法。首先，基于Retinex理论模型，利用光照估计算法将曝光序列图像分为入射光分量序列和反射光分量序列，然后分别采用不同的融合方法对这两组序列进行处理。对于入射光分量，要保证场景的全局亮度的变化特性并且削弱过曝光和欠曝光区域的影响；而对于反射光分量，要采用适度曝光的评价参数来更好地保留场景的色彩及细节信息。分别从主观和客观两方面对所提算法进行了分析。实验结果表明，同传统基于图像域合成的算法相比，该算法在结构相似度（SSIM）上平均提升了1.7%，另外在图像色彩和局部细节上的处理效果更好。     

图像分解与色彩先验下的多曝光图像融合

目的 多曝光图像融合（multi-exposure fusion，MEF）是利用一组不同曝光度的低动态范围（low dynamic range，LDR）图像进行合成，得到类似高动态范围（high dynamic range，HDR）图像视觉效果图像的过程。传统多曝光图像融合在一定程度上存在图像细节信息受损、边界不清晰以及部分色彩失真等问题。为了充分综合待融合图像的有效信息，提出了一种基于图像分解和色彩先验的双尺度多曝光图像融合方法。方法 使用快速导向滤波进行图像分解，分离出细节层对其进行增强处理，保留更多的细节信息，同时减少融合图像的光晕伪影；根据色彩先验，利用亮度和饱和度之差判断图像曝光程度，并联合亮度与饱和度之差以及图像对比度计算多曝光图像融合权重，同时保障融合图像的亮度和对比度；利用导向滤波对权重图进行优化，抑制噪声，增加像素之间的相关性，提升融合图像的视觉效果。结果 在24组多曝光图像序列上进行实验，从主观评价角度来看，该融合方法能够提升图像整体对比度及色彩饱和度，并兼顾过曝光区域和欠曝光区域的细节提升。从客观评价标准分析，采用两种不同的多曝光图像序列融合结果的质量评估算法，评价结果显示融合性能均有所提高，对应的指标均值分别为0.982和0.970。与其他对比算法的数据结果比较，在两种不同的结构相似性指标上均有所提升，平均提升分别为1.2%和1.1%。结论 通过主观和客观评价，证实了所提方法在图像对比度、色彩饱和度以及细节信息保留的处理效果十分显著，具有良好的融合性能。     

高动态范围成像技术中的鬼影检测与去除方法综述

由于广泛的实用价值与理论价值,高动态范围成像(HDRI)技术成为图像处理领域的一个研究热点,如何检测及去除成像过程中产生的干扰影像(即“鬼影”)也引起了研究者的广泛关注。将鬼影检测与去除方法按照运动物体是否属于拍摄目标及算法操作域进行系统分类,将鬼影检测算法分为无参考图像、有参考图像两大类并将每一大类分为辐射域检测、图像域检测两类,将鬼影去除算法分为辐射域去除、图像域去除两大类,对其中每一类算法分别全面综述了其特点及最新研究成果,并对不同方法的优缺点进行了比较分析。最后总结了不同方法的适用条件并给出了关于这一课题未来发展的思考。     

Interactive HDR lighting of dynamic participating media

In this paper, we present two optimization techniques to light and render volumetric data of inhomogeneous participating media. Both are independent of the lighting model selected. We use an implementation of the ray marching algorithm to approximate the Radiance Transfer Equation. The system can calculate single scattering in time-varying isotropic participating media with the incident field being modeled as a high dynamic range (HDR) environment map. We can use dynamic lighting (with certain restrictions) and free camera movement without using any precomputations while achieving interactive frame rates. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.

A modified Multi Scale Retinex algorithm with an improved global impressionof brightness for wide dynamic range pictures

This paper presents a new method of compressing the dynamic range of wide dynamic range scenes. This method is based on the Multi Scale Retinex algorithm. It improves the results of the original Multi Scale Retinex algorithm in a way that retains the global brightness contrast and the natural impression of the resulting image by recombining the original picture in a certain weight. Further improvement of the global brightness contrast is achieved by adjusting the histogram of the resulting picture. The paper explores the performance of this modified algorithm on different wide dynamic range scenes and points out its advantages over other dynamic range compression algorithms.Received: 7 November 2002, Accepted: 1 December 2003, Published online: 17 August 2004 Correspondence to: Orly Yadid-Pecht     

Image sequence enhancements based on the normal component of image motion

Huang and Hsu (1981) describe an image sequence enhancement algorithm based on computing motion vectors between successive frames and using these vectors to determine the correspondence between pixels for frame averaging. In this note, we demonstrate that it may be sufficient to use only the components of the motion vectors in the gradient direction (called the normal components) to perform the enhancement.     

Optical-digital correlator with increased dynamic range using spatially varying pixels exposure technique

In this work the application of the spatially varying pixels exposure technique for obtaining linear high dynamic range (HDR) images of correlation signals by Bayer-covered photo sensors is presented. Bayer colour filters array is considered as an array of attenuating filters in the quasimonochromatic light. The procedure of HDR images reconstruction using data from neighbour pixels and preliminary obtained correction coefficients is described. Experimental results of HDR registration of correlation signals are provided. It is shown that reconstructed HDR correlation signals are linear as normal signals are. The increase of dynamic range of signal’s registration from 58 dB up to 73 dB is obtained. Results on recognition of test objects with normal and HDR registration are discussed. The article is published in the original.     

High dynamic range optimal fuzzy color image enhancement using Artificial Ant Colony System

This paper presents a novel approach for the enhancement of high dynamic range color images using fuzzy logic and modified Artificial Ant Colony System techniques. Two thresholds, the lower and the upper are defined to provide an estimate of the underexposed, mixed-exposed and overexposed regions in the image. The red, green and blue (RGB) color space is converted into Hue Saturation and Value (HSV) color space so as to preserve the chromatic information. Gaussian MFs suitable for the underexposed and overexposed regions of the image are used for the fuzzification. Parametric sigmoid functions are used for enhancing the luminance components of under and over-exposed regions. Mixed-exposed regions are left untouched throughout the process. An objective function comprising of Shannon entropy function as the information factor and visual appeal indicator is optimized using Artificial Ant Colony System to ascertain the parameters needed for the enhancement of a particular image. Visual appeal is preferred over the consideration of entropy so as to make the image human-eye-friendly. Separate power law operators are used for the saturation adjustment so as to restore the lost information. On comparison, this approach is found to be better than the bacterial foraging (BF)-based approach [1].     

大动态范围多曝光图像融合方法

提出一种基于动态范围扩展的多曝光图像多尺度融合方法。讨论融合目标与动态范围分布、细节及颜色的处理策略。在融合规则中提出全局动态范围系数来反映全局照度范围,并指导亮度融合来突出融合结果的动态范围;使用局部对比度和色彩饱和度来反映原始图像的曝光程度,并用于指导色彩融合;使用小波分析作为多尺度融合工具。对算法进行测试并与已有算法的结果进行信息熵和动态范围比较,结果表明该算法对于信息熵和动态范围均有提高。     

基于鲁棒估计的Retinex图像增强方法

针对原变分Retinex方法的人工伪影问题,指出理想重建光照应该具有分区域恒常的特性,提出一种以阴影边界作为出格点、基于鲁棒估计的变分Retinex图像增强方法。用合成图像与实际图像进行实验表明,本改进方法不仅可以有效压缩图像动态范围,显示淹没在阴影区域的细节,而且解决了原Retinex方法的伪影和扭曲等问题。     

基于动态范围调整的指纹图像增强方法

采用基于动态范围调整的方法,并适当地把图像最亮和最暗附近很少量灰度级像素点滤除,对图像灰度进行线性展宽,实现图像灰度动态范围的自动调整,提高图像的对比度。实验结果表明,该方法可有效地滤除在灰度边界值附近的灰度干扰,图像的质量和对比度明显提高,图像的亮区和暗区的细节都有明显增强,而且处理速度快,鲁棒性好。     

Adaptive color image watermarking based on a modified improved pixel-wise masking technique

In this paper, a family of modified wavelet-based watermarking techniques is proposed. This family of techniques is based on the improved pixel-wise (PW) watermarking scheme. The basic proposed algorithm considerably improves the PSNR of the watermarked image (in the range of 2.20–7.28 dB), and is based on selecting specific locations in the three detailed sub-bands of the first level of the DWT decomposition of the image. The selective nature of the modified PW method (denoted as selective PW: SPW) allows the scheme to be adaptive in terms of the imperceptibility and the watermark size. Also, the PW and SPW methods were extended to be implemented with color images: (1) grayscale-wise PW method (G-PW) that embeds the watermark in the Y component of the YCbCr model. (2) Multi spectral-PW method (MS-PW) that embeds the watermark in the R, G, and B layers independently. (3) Multi spectral-SPW method (MS-SPW) that gains high PSNR value compared with MS-SPW, and (4) multi spectral-maximum PW method (MS-MPW) which is proposed to improve the PSNR value as well as the level of watermarking security, when compared with MS-PW method.     

基于自适应分块的动态场景HDR图像合成算法

通过提出基于梯度上升优化处理的自适应分块算法与基于图像序列梯度域运动检测与去除相结合的方法,自适应调整分块大小及动态区域块的融合权值,最终达到混淆去除的目的.同时,利用Gaussian中心函数窗口滤波,去除在分块融合过程中引入的块边缘不连续性痕迹.实验结果表明,该方法能快速有效地增强多曝光图像融合生成HDRI并去除混淆问题.     

Image retrieval based on shape similarity by edge orientation autocorrelogram

This paper introduces a new feature vector for shape-based image indexing and retrieval. This feature classifies image edges based on two factors: their orientations and correlation between neighboring edges. Hence it includes information of continuous edges and lines of images and describes major shape properties of images. This scheme is effective and robustly tolerates translation, scaling, color, illumination, and viewing position variations. Experimental results show superiority of proposed scheme over several other indexing methods. Averages of precision and recall rates of this new indexing scheme for retrieval as compared with traditional color histogram are 1.99 and 1.59 times, respectively. These ratios are 1.26 and 1.04 compared to edge direction histogram.     

基于自适应分割的动态面光源图像空间绘制

针对图像空间绘制技术中可见性积分的计算不能达到实时,并且无法捕捉由面光源上辐射度变化引起的着色点亮度变化这两个问题,提出了一种基于自适应的空间划分技术的、在图像空间中对动态面光源效果进行绘制的方法.该方法将场景中的物体根据深度及分布情况,自适应地划分为非均匀的体素,同时构建场景中深度和法向变化量的多级纹理,并利用存储在这些体素和纹理中的信息对着色点进行快速的可见性积分和相应的光照度计算.     

基于相机响应曲线的高动态范围图像融合

高动态范围成像技术由于能够更加真实地再现成像目标及周围场景,在军事、航天等领域具有重要的研究价值。首先利用佳能1DC针对同一场景拍摄不同曝光量的序列图像,通过推导计算获得彩色图像各通道的相机响应曲线;然后通过建立图像灰度值与辐照度之间的照度映射获得一幅高动态范围的辐照度图像;其次利用基于双边滤波色调映射算法对获得的高动态范围图像进行压缩;最后通过基于镜面反射白平衡算法对图像进行色彩校正,从而获得拍摄场景的高动态范围图像。抽取不同帧数的实验拍摄图像对所提算法进行有效性验证,通过实验结果分析该算法实现高动态范围图像融合所需最少图像帧数为4帧。     

Missile target automatic recognition from its decoys based on image time-series

As the development of the technology for radar target recognition, missile target automatic recognition has received considerable attention in recent years. Missile target, compared with the plane target, is hard to recognize for its smallness, feebleness and maneuver. In this paper, a new recognition method based on radar image time-series, which can significantly reduce the recognition time and classification error, is proposed. The image time-series are produced by range instantaneous Doppler imaging algorithm firstly, and then cross-range scaling of the images is processed. In particular, the inertia ratio, extracted from the obtained image time-series, is introduced to distinguish the missile from decoys. Furthermore, the effectiveness of this method is demonstrated by application to simulated data and it has been shown that this method has the potential to be used in a number of real-time applications.