Noise-proofing the doubly SH-projected coefficients for synthesizing images under environment lighting

The brute-force way to synthesize images of an object under various lighting environments is very time consuming. To speed up the synthesizing process, we can model the bidirectional reflectance distribution function (BRDF) of each surface element as a spherical harmonic (SH) coefficient matrix based on the double SH projection. With the SH coefficient matrices of all surface elements, we can relight an object under the global illumination. However, applying the classical least square method for the double SH projection, the returned SH coefficients are prohibitively large in magnitude because samples are available on the upper hemisphere only. Hence, the synthesizing process is very sensitive to small quantization noise introduced by the compression process. Existing methods to this noise-sensitivity problem mainly focus on the single SH projection. It should be noticed that the double SH projection further amplifies the artifacts. Straightforwardly extending existing methods to the double SH projection may not be theoretically nor practically feasible. In this paper, we present a robust estimation method for the double SH projection. With the proposed method, severe artifacts in synthesized images can be significantly reduced. Comparison with the existing Sloan's method is performed to support the effectiveness of the proposed method.     

一种基于小波系数上下文模型的图像压缩方法

提出了二种新颖的基于小波系数上下文模型的图像压缩方法，该方法通过量化当前系数的线性预测值形成上下文．进行自适应的算术编码；同时利用了小波变换的多分辨率性质，以渐近分辨率的方式压缩图片，具有分辨率可扩展性。实验结果表明，该方法获得的无损压缩比高于SPIHT和用于JPEG2000的EBCOT，在各分辨率下的压缩比也高于EBCOT．压缩时间也比EBCOT要少。     

一种基于JPEG2000标准的数字图像加密算法

针对最新的图像压缩标准JPEG2000,提出了一种在JPEG2000压缩过程中实时对小波系数进行加密的方法.在具体算法上采用本文提出的小波置乱(简称为OCWF)方法并结合符号加密来实现对小波系数的实时加密.实验结果表明,该方法具有加密效果好、加密开销少、对压缩性能影响小等优点,且完全适合高压缩率的有损压缩,可以满足版权保护等应用场合的需要.     

GPU-friendly rendering for illumination adjustable images

An illumination adjustable image (IAI) contains a large number of pre-recorded reference images under various lighting directions. It describes the appearance of a scene illuminated under various lighting directions. Synthesized images about the scene illuminated by complicated lighting conditions are generated from those reference images. This paper presents practical and real-time rendering methods for IAIs based on spherical Gaussian kernel functions (SGKFs). The lighting property of an IAI is represented by a few number of lightmaps. With those lightmaps, we can use consumer-level graphics processing units (GPUs) to perform the rendering process. The rendering methods for directional light source, point light source and slide projector are discussed. Compared with the conventional spherical harmonic (SH) approach, the proposed SGKF approach offers similar distortion performance but it consumes less graphics memory and has a faster rendering speed.     

一种嵌入可读水印的自适应盲水印算法

本文提出了一种基于DWT的嵌入可读水印的自适应盲水印算法,通过分析图像经离散小波变换后细节子带系数的特性,把细节子带系数的均值和方差作为水印信息的一部分来自适应地修改图像小波分解后某些细节子带的系数值,在满足水印不可感知性的条件下自适应地嵌入水印信息,实现了水印不可感知性和鲁棒性之间的折衷.同时,水印的提取无须求助于原图像,很好的实现了水印的盲检测.这里的水印是一幅有实际意义的二值图像.实验结果和攻击测试表明,本文提出的算法对JPEG/JPEG2000压缩、添加噪声、剪切、像素移位等多种攻击有较强的鲁棒性,同时对直方图均衡化、对比度调整和高斯滤波等图像处理操作也具有一定的抵抗能力.     

三维图像的任意形状ROI小波零块压缩编码算法

感兴趣区(ROI)编码是在JPEG2000中提出的一种重要的技术,然而JPEG2000算法却无法同时支持任意形状ROI和任意提升因子.本文提出了一种基于任意形状ROI和3D提升小波零块编码的3D体数据图像压缩算法.新的算法支持ROI内外从有损到无损的编码.一种简单的任意形状无损ROI掩码(Mask)生成方法被提出.考虑到3D子带的特点,我们采用改进的3DSPECK零块算法对变换后的系数进行编码.一些其它支持任意形状ROI编码的算法也在本文中被评估,试验显示本文算法具有更好的编码性能.     

An RBF-based compression method for image-based relighting.

In image-based relighting, a pixel is associated with a number of sampled radiance values. This paper presents a two-level compression method. In the first level, the plenoptic property of a pixel is approximated by a spherical radial basis function (SRBF) network. That means that the spherical plenoptic function of each pixel is represented by a number of SRBF weights. In the second level, we apply a wavelet-based method to compress these SRBF weights. To reduce the visual artifact due to quantization noise, we develop a constrained method for estimating the SRBF weights. Our proposed approach is superior to JPEG, JPEG2000, and MPEG. Compared with the spherical harmonics approach, our approach has a lower complexity, while the visual quality is comparable. The real-time rendering method for our SRBF representation is also discussed.     

Uniformly sampling multi-resolution analysis for image-based relighting

Image-based relighting allows us to efficiently light a scene under complicated illumination conditions. However, the traditional cubemap based multi-resolution analysis unevenly samples the spherical surface, with a higher sampling rate near the face corners and a lower one near the face centers. The non-uniformity penalizes the efficiency of data representation. This paper presents a uniformly sampling multi-resolution analysis approach, namely the icosahedron spherical wavelets (ISW), for image-based relighting under time-varying distant environment. Since the proposed ISW approach provides a highly uniform sampling distribution over the spherical domain, we thus can efficiently handle high frequency variations locally in the illumination changes as well as reduce the number of wavelet coefficients needed in the renderings. Furthermore, visual artifacts are demonstrated to be better suppressed in the proposed ISW approach. Compared with the traditional cubemap based multi-resolution analysis approach, we show that our approach can effectively produce higher quality image sequences that are closer to the ground truth in terms of percentage square errors.     

A lossless compression algorithm of remote sensing image for space applications

A simple and adaptive lossless compression algorithm is proposed for remote sensing image compression, which includes integer wavelet transform and the Rice entropy coder. By analyzing the probability distribution of integer wavelet transform coefficients and the characteristics of Rice entropy coder, the divide and rule method is used for high-frequency sub-bands and low-frequency one. High-frequency sub-bands are coded by the Rice entropy coder, and low-frequency coefficients are predicted before coding. The role of predictor is to map the low-frequency coefficients into symbols suitable for the entropy coding. Experimental results show that the average Comprcssion Ratio （CR） of our approach is about two, which is close to that of JPEG 2000. The algorithm is simple and easy to be implemented in hardware. Moreover, it has the merits of adaptability, and independent data packet. So the algorithm can adapt to space lossless compression applications.     

一种基于混合整型变换和3D-SPIHT的高光谱图像嵌入式无损压缩方法

利用高光谱图像空间、谱间相关性不同的特点,本文提出了一种基于混合整型变换和三维分层树集合划分算法(3D-SPIHT)的高光谱图像无损压缩方法,首先将波段进行分组,针对每一分组,采用不同的整型变换技术去相关,然后对变换系数进行系数重组,采用高效的基于小波系数特点的3D-SPIHT编码方法得到嵌入式码流,具有一定的抗误码性能.实验结果表明,该方法能够有效的去除高光谱图像的空间和谱间相关性,与现有的国际标准JPEG-LS、JPEG2000和基于三维离散余弦变换(3D-DCT)或三维离散小波变换(3D-DWT)的编码方法相比,压缩后的平均比特率均有明显降低.     

基于条件共生概率矩阵的移位JPEG双压缩检测

针对合成JPEG图像的小区域移位JPEG双压缩(SD-JPEG压缩)篡改问题,提出一种基于条件共生概率矩阵(CCPM)的SD-JPEG压缩篡改检测算法。为了减小图像内容的影响,增强SD-JPEG压缩效应,首先对JPEG量化的离散余弦变换(DCT)系数的幅度矩阵进行水平、垂直、主对角和副对角4个方向差分和阈值化处理,然后使用CCPM对这4个阈值化的差分矩阵进行建模,选取CCPM的元素作为特征数据,并用主分量分析(PCA)对其降维处理,最后通过支持向量机(SVM)技术判决图像块是否经过SD-JPEG压缩。实验结果验证了本文算法的有效性。     

Lossless image compression with projection-based and adaptive reversible integer wavelet transforms

Reversible integer wavelet transforms are increasingly popular in lossless image compression, as evidenced by their use in the recently developed JPEG2000 image coding standard. In this paper, a projection-based technique is presented for decreasing the first-order entropy of transform coefficients and improving the lossless compression performance of reversible integer wavelet transforms. The projection technique is developed and used to predict a wavelet transform coefficient as a linear combination of other wavelet transform coefficients. It yields optimal fixed prediction steps for lifting-based wavelet transforms and unifies many wavelet-based lossless image compression results found in the literature. Additionally, the projection technique is used in an adaptive prediction scheme that varies the final prediction step of the lifting-based transform based on a modeling context. Compared to current fixed and adaptive lifting-based transforms, the projection technique produces improved reversible integer wavelet transforms with superior lossless compression performance. It also provides a generalized framework that explains and unifies many previous results in wavelet-based lossless image compression.     

Design of signal-adapted multidimensional lifting scheme for lossy coding

This paper proposes a new method for the design of lifting filters to compute a multidimensional nonseparable wavelet transform. Our approach is stated in the general case, and is illustrated for the 2-D separable and for the quincunx images. Results are shown for the JPEG2000 database and for satellite images acquired on a quincunx sampling grid. The design of efficient quincunx filters is a difficult challenge which has already been addressed for specific cases. Our approach enables the design of less expensive filters adapted to the signal statistics to enhance the compression efficiency in a more general case. It is based on a two-step lifting scheme and joins the lifting theory with Wiener's optimization. The prediction step is designed in order to minimize the variance of the signal, and the update step is designed in order to minimize a reconstruction error. Application for lossy compression shows the performances of the method.     

CCSDS压缩算法在红外导引头图像传输中的应用

针对军用探测中红外导引头得到的红外图像需要快速、安全、高效地传输的问题,研究了红外图像的压缩问题.通过各种算法比较,发现空间数据系统咨询委员会(CCSDS)推荐的基于小波变换的图像压缩算法有更易于硬件实现的特点.并且当图像压缩比大于30倍时,图像的失真也是能够接受的.并根据红外图像及其小波变换后系数的各子带直方图分布的特点,提出了一种改进的压缩算法.该算法是基于CCSDS推荐的压缩算法,并通过重新分配小波变换后各子带重要性因子及选择RICE中的预测器使其更适合于红外图像的压缩.同时对该算法产生的压缩数据流在无线传输过程中的容错性问题,提出了的建议及方法.经过仿真,该算法压缩效果同JPEG2000相近,且经过改进后的算法与原算法相比,PSNR提高了0.2dB.     

Video compression using spatiotemporal regularity flow.

We propose a new framework in wavelet video coding to improve the compression rate by exploiting the spatiotemporal regularity of the data. A sequence of images creates a spatiotemporal volume. This volume is said to be regular along the directions in which the pixels vary the least, hence the entropy is the lowest. The wavelet decomposition of regularized data results in a fewer number of significant coefficients, thus yielding a higher compression rate. The directions of regularity of an image sequence depend on both its motion content and spatial structure. We propose the representation of these directions by a 3-D vector field, which we refer to as the spatiotemporal regularity flow (SPREF). SPREF uses splines to approximate the directions of regularity. The compactness of the spline representation results in a low storage overhead for SPREF, which is a desired property in compression applications. Once SPREF directions are known, they can be converted into actual paths along which the data is regular. Directional decomposition of the data along these paths can be further improved by using a special class of wavelet basis called the 3-D orthonormal bandelet basis. SPREF -based video compression not only removes the temporal redundancy, but it also compensates for the spatial redundancy. Our experiments on several standard video sequences demonstrate that the proposed method results in higher compression rates as compared to the standard wavelet based compression.     

Wavelet based watermarking method for digital images using thehuman visual system

A wavelet based multiresolution watermarking method using the human visual system (HVS) is proposed, with the number of watermarks embedded proportional to the energy contained in each band. Experiments show that the proposed three-level wavelet based watermarking method is robust to some attacks such as, for example, joint photographic experts group (JPEG) compression, smoothing, cropping and collusion     

自适应小波变换及其在JPEG 2000中的应用

针对传统的线性小波分解不能很好保留图像边缘信息．且在跃变点处会出现大的小波系数而不利于图像压缩，提出了一种新的基于提升方案的二维不可分离自适应小波变换（AWT）方案。在该方案中，根据局部信息自适应地将图像分为平滑区域和非平滑区域．在不同区域选取不同的更新和预测函数。通过在JPEG2000中的实验结果表明，用该方法进行图像分解。低频近似图像保留了细节信息，边缘清晰；对双边AWT后的图像压缩，性能优于JPEG2000的5／3小波和9／7小波，峰值信噪比（PSNR）提高0．5～2．0dB。     

用于JPEG2000图像认证的半脆弱性数字水印算法

本文给出一种适用于JPEG2000图像认证的半脆弱性数字水印算法,该算法与JPEG2000编、解码器相结合,它根据JPEG2000图像压缩过程中的不变参量进行水印生成和嵌入调制,利用小波变换特性对图像篡改区域进行定位.实验表明,采用该算法实现的水印不仅具有良好的视觉透明性,而且还有较佳的篡改区域指示功能.     

一个优化小波块量化矩阵的算法

小波变换以其良好的空间－频率局部特性,在图像编码标准JPEG2000和MPEG4中占据了重要位置.本文选用正交小波基对图像做小波变换,然后重新组织小波系数成小波块,最后提出了一个构造小波块量化矩阵以产生最优比特分配的算法.本算法用一种新的方式统计小波系数分布,并结合人体视觉系统的特点,采用动态策略在很大的比特率范围内产生最优的小波块量化矩阵.     

基于格的灰度级水印技术

提出一个新的灰度级水印算法．首先，使用量化技术对灰度级水印进行预处理，实现灰度级水印的数据压缩；然后，对原始图像进行小波分解，在小波域中使用格矢量量化技术构造水印的嵌人和提取算法．提取水印不需要原图像．为增强水印的安全性，使用混沌序列作为密钥对水印序列进行调制．实验结果表明，与同类算法相比该算法在获得较好感知质量含水印图像的同时提高了水印的鲁棒性．