Space-variant nonorthogonal structure CMOS image sensor design

A CMOS log-polar image sensor has been designed and fabricated. As a result, a systematic approach has been proposed to design space-variant sensors and layouts. The pixels in this sensor are distributed in a polar fashion; the image plane consists of concentric rings containing the elementary sensing cells. Such a structure, where polygons use any space orientation, does not match very well with current design tools and CMOS fabrication processes. An approach to design nonorthogonal repetitive structures using standard fabrication processes and computer-aided design (CAD) tools is presented. The result of this work is an image sensor, with log-polar structure, suitable for image processing since the log-polar mapping has interesting mathematical and image data reduction properties     

Image Registration Using Adaptive Polar Transform

Image registration is an essential step in many image processing applications that need visual information from multiple images for comparison, integration, or analysis. Recently, researchers have introduced image registration techniques using the log-polar transform (LPT) for its rotation and scale invariant properties. However, it suffers from nonuniform sampling which makes it not suitable for applications in which the registered images are altered or occluded. Inspired by LPT, this paper presents a new registration algorithm that addresses the problems of the conventional LPT while maintaining the robustness to scale and rotation. We introduce a novel adaptive polar transform (APT) technique that evenly and effectively samples the image in the Cartesian coordinates. Combining APT with an innovative projection transform along with a matching mechanism, the proposed method yields less computational load and more accurate registration than that of the conventional LPT. Translation between the registered images is recovered with the new search scheme using Gabor feature extraction to accelerate the localization procedure. Moreover an image comparison scheme is proposed for locating the area where the image pairs differ. Experiments on real images demonstrate the effectiveness and robustness of the proposed approach for registering images that are subjected to occlusion and alteration in addition to scale, rotation, and translation.     

Wide-Angle Foveation for All-Purpose Use

This paper proposes a model of a wide-angle space-variant image that provides a guide for designing a fovea sensor. First, an advanced wide-angle foveated (AdWAF) model is formulated, taking all-purpose use into account. This proposed model uses both Cartesian (linear) coordinates and logarithmic coordinates in both planar projection and spherical projection. Thus, this model divides its wide-angle field of view into four areas, such that it can represent an image by various types of lenses, flexibly. The first simulation compares with other lens models, in terms of image height and resolution. The result shows that the AdWAF model can reduce image data by 13.5%, compared to a log-polar lens model, both having the same resolution in the central field of view. The AdWAF image is remapped from an actual input image by the prototype fovea lens, a wide-angle foveated (WAF) lens, using the proposed model. The second simulation compares with other foveation models used for the existing log-polar chip and vision system. The third simulation estimates a scale-invariant property by comparing with the existing fovea lens and the log-polar lens. The AdWAF model gives its planar logarithmic part a complete scale-invariant property, while the fovea lens has 7.6% error at most in its spherical logarithmic part. The fourth simulation computes optical flow in order to examine the unidirectional property when the fovea sensor by the AdWAF model moves, compared to the pinhole camera. The result obtained by using a concept of a virtual cylindrical screen indicates that the proposed model has advantages in terms of computation and application of the optical flow when the fovea sensor moves forward.     

基于对数极坐标变换的目标识别算法

针对二维ISAR像的空中目标识别问题,提出了一种新的识别算法。首先通过对数极坐标变换,将笛卡儿坐标系下的尺度、旋转变换转变成对数极坐标系下的平移变换,然后对新坐标系下的图像进行二维傅里叶变换,利用傅里叶变换模值的平移不变性,得到具有尺度、旋转不变性的特征矩阵,最后与模板的特征矩阵进行矩阵相关,识别分类。用实测数据进行了验证,证明了算法具有较快的速度和较好的识别结果。     

Precision SAR processing using chirp scaling

A space-variant interpolation is required to compensate for the migration of signal energy through range resolution cells when processing synthetic aperture radar (SAR) data, using either the classical range/Doppler (R/D) algorithm or related frequency domain techniques. In general, interpolation requires significant computation time, and leads to loss of image quality, especially in the complex image. The new chirp scaling algorithm avoids interpolation, yet performs range cell migration correction accurately. The algorithm requires only complex multiplies and Fourier transforms to implement, is inherently phase preserving, and is suitable for wide-swath, large-beamwidth, and large-squint applications. This paper describes the chirp scaling algorithm, summarizes simulation results, presents imagery processed with the algorithm, and reviews quantitative measures of its performance. Based on quantitative comparison, the chirp scaling algorithm provides image quality equal to or better than the precision range/Doppler processor. Over the range of parameters tested, image quality results approach the theoretical limit, as defined by the system bandwidth     

超高分辨率机载聚束SAR空变运动误差校正

该文分析了机载聚束式合成孔径雷达(SAR)运动误差的空变性,推导了空变的运动误差与聚束扫描角度、照射区域大小及天线下视角等参数之间的定量关系,针对超高分辨率机载聚束SAR成像运动误差空变效应明显的问题,提出一种基于chirp扰动的距离重采样新方法,并结合图像方位分块处理技术构建了比较完善的运动补偿方案,以弥补传统运动补偿方法在超高分辨率机载SAR成像中的不足。最后,用仿真实验验证了方案的有效性。     

基于对数极坐标映射的图像倾斜检测

图像倾斜角的检测和校正是图像预处理中很重要的环节。本文推广了Fourier变换检测文本倾角的方法,并将其应用到更多类型的图像。算法将图像的Fourier谱映射到对数极坐标域,并分析计算Fourier谱在角度轴上的投影峰值,最终获得图像的倾斜角。实验结果表明,此算法适用范围广,计算量小,且具有很好的鲁棒性。     

基于对数极坐标变换的图像匹配算法

相位相关算法通常只具有平移不变性,而不具有尺度和旋转不变性,因此无法对存在尺度和旋转变化的图像进行图像匹配.而对数极坐标变换可以将图像在笛卡儿坐标系下的尺度和旋转变化变换为沿对数极坐标系的平移运动,具有较好的尺度和旋转不变性.文中提出了一种基于图像对数极坐标变换的相关匹配算法.仿真结果表明基于对数极坐标变换的相位相关算法可以针对具有尺度和旋转变换的图像进行很好的匹配,并能检测出图像的旋转角度及尺度参数.     

基于最小熵DCFT的双基地SAR多普勒参数估计

多普勒参数估计是SAR成像技术研究中的一项关键技术,多普勒参数估计精度将直接影响机载双基地SAR系统成像质量,为了实现对感兴趣目标区域有效地成像,需要对回波信号的参数进行准确估计。本文提出基于最小熵的离散调频傅里叶法(DCFT),该方法基于线性调频信号,可同时估计多普勒质心和多普勒斜率,并用RD算法对双基地SAR仿真数据成像,通过仿真验证了该方法的性能。     

分数域啁啾滤波及其在数字图像处理中的应用

讨论了分数域啁啾滤波的基本原理,同时将光学中的分数傅里叶变换引入到数字图像处理中,提出了一种分数域滤波去除影响数字图片质量之啁啾噪声的新方法,比较了分数域啁啾滤波和常规傅里叶频谱面上的滤波,获得了满意的模拟结果。     

Image registration using log-polar mappings for recovery of large-scale similarity and projective transformations.

This paper describes a novel technique to recover large similarity transformations (rotation/scale/translation) and moderate perspective deformations among image pairs. We introduce a hybrid algorithm that features log-polar mappings and nonlinear least squares optimization. The use of log-polar techniques in the spatial domain is introduced as a preprocessing module to recover large scale changes (e.g., at least four-fold) and arbitrary rotations. Although log-polar techniques are used in the Fourier-Mellin transform to accommodate rotation and scale in the frequency domain, its use in registering images subjected to very large scale changes has not yet been exploited in the spatial domain. In this paper, we demonstrate the superior performance of the log-polar transform in featureless image registration in the spatial domain. We achieve subpixel accuracy through the use of nonlinear least squares optimization. The registration process yields the eight parameters of the perspective transformation that best aligns the two input images. Extensive testing was performed on uncalibrated real images and an array of 10,000 image pairs with known transformations derived from the Corel Stock Photo Library of royalty-free photographic images.     

线性调频激励的红外热波成像检测技术

线性调频激励的红外热波成像检测技术是一种基于线性调制热波信号处理的主动式红外热成像技术,能够弥补传统红外锁相热像检测的单一调制热波只能探测相应扩散深度缺陷的不足,可准确检测不同深度范围内的缺陷形状及尺寸。阐述了线性调频红外热波成像检测技术的原理、分析方法和实验。采用有限元方法对线性调频啁啾(Chirp)规律变化热流在构件中的传递过程进行了分析。利用相关算法计算了表面温度(热波)信号的相关峰值及其对应的时间,形成了表面温度相关峰值图像与峰值时间图像。利用Chirp规律调制卤素光源作为热激励源对金属平底孔试件进行激励加载,通过Jade MWIR 550 焦平面红外热像仪进行图像序列采集。分别利用时域相关处理与频域FFT扫描得到了表面温度(热波)信号的相关峰值及对应时间图像和不同频率下的相位图像。试验结果表明,在给定激励条件下,相关峰值图像和频域相位图像能够可靠地确定不同深度缺陷的几何特征。     

一种基于波程差补偿的InISAR图像配准方法

逆合成孔径雷达(ISAR)图像配准是干涉逆合成孔径雷达(InISAR)成像领域一个关键的课题,可以实现同一散射点在不同ISAR图像中的对齐,以便于后续的ISAR图像干涉处理。该文分析了ISAR图像失配准的原因,即散射点到不同天线之间的波程差,并据此提出一种基于波程差补偿的方法来实现不同天线ISAR图像之间的精确配准。首先通过调频傅里叶变换估计目标相对于雷达的转速;进一步根据波程差与目标转动角速度的关系构建补偿相位消除散射点到不同天线间的波程差,并通过2维傅里叶变换获得配准之后的ISAR图像。最后利用干涉处理获得目标真实的3维结构。该文方法可以在回波域通过波程差补偿实现ISAR图像配准,配准之后的各散射点在图像中的位置相同;而经过相关法配准之后的ISAR图像中的各散射点之间有一个像素单元的错位,即该方法的配准效果更精确。此外,基于相关法的图像配准方法耗时达到万秒级,而基于该方法的ISAR图像配准时间仅为秒级,即该方法计算效率更高。最终的InISAR 3维成像结果中,该方法的散射点坐标重构误差为0.3034,而基于相关法的成像结果的误差(45.8529)远大于此。因此,基于所提出方法的InISAR 3维成像结果精度更高。      

A log-polar image sensor fabricated in a standard 1.2-μm ASICCMOS process

A CMOS log-polar or foveated image sensor for use in mobile robotic and machine vision applications has been designed, fabricated, and tested. The sensor benefits from a high degree of integration, minimal power consumption, and ease of manufacture due to the use of a standard 1.2 μm ASIC CMOS process. The sensor is composed of two distinct CMOS imager arrays which together solve the problem of obtaining good image resolution over a wide field of view. With resolution sensing is accomplished with a 40×40 array of individual pixels each measuring 9.6 μm on a side. A wide field of view is provided by an array of 64×16 pixels arranged on a log-polar grid. The maximum measured dynamic range for the fabricated log-polar array is 46 dB, while the lowest observed fixed-pattern noise is 0.5% of saturation. Combined power consumption of both arrays is under 2 mW when operating from a single 5-V supply at a frame rate of 30 frames/s     

Family of scaling chirp functions, diffraction, and holography

It is observed that diffraction is a convolution operation with a chirp kernel whose argument is scaled. Family of functions obtained from a prototype by shifting and argument scaling form the essential ground for wavelet framework. Therefore, a connection between diffraction and wavelet transform is developed. However, wavelet transform is essentially prescribed for time-frequency and/or multiresolution analysis which is irrelevant in our case. Instead, the proposed framework is useful in various location-depth type of analysis in imaging. The linear transform when the analyzing functions are the chirps is called the scaling chirp transform. The scaled chirp functions do not satisfy the commonly used admissibility condition for wavelets. However, it is formally shown that these neither band nor time limited signals can be used as wavelet functions and the inversion is still possible. Diffraction and in-line holography are revisited within the scaling chirp transform context. It is formally proven that a volume in-line hologram gives perfect reconstruction. The developed framework for wave propagation based phenomena has the potential of advancing both signal processing and optical applications     

Discrete chirp-Fourier transform and its application to chirp rateestimation

The discrete Fourier transform (DFT) has found tremendous applications in almost all fields, mainly because it can be used to match the multiple frequencies of a stationary signal with multiple harmonics. In many applications, wideband and nonstationary signals, however, often occur. One of the typical examples of such signals is chirp-type signals that are usually encountered in radar signal processing, such as synthetic aperture radar (SAR) and inverse SAR imaging. Due to the motion of a target, the radar return signals are usually chirps, and their chirp rates include the information about the target, such as the location and the velocity. In this paper, we study discrete chirp-Fourier transform (DCFT), which is analogous to the DFT. Besides the multiple frequency matching similar to the DFT, the DCFT can be used to match the multiple chirp rates in a chirp-type signal with multiple chirp components. We show that when the signal length N is prime, the magnitudes of all the sidelobes of the DCFT of a quadratic chirp signal are 1, whereas the magnitude of the mainlobe of the DCFT is √N. With this result, an upper bound for the number of the detectable chirp components using the DCFT is provided in terms of signal length and signal and noise powers. We also show that the N-point DCFT performs optimally when N is a prime     

快速超复数傅氏变换和超复数互相关的新算法及应用

超复数把彩色图像作为一个矢量整体进行处理,与传统算法相比,它能更好地描述图像的色彩关联,超复数互相关已广泛应用到彩色图像处理的各个领域.本文首先分析和介绍了目前的实现二维超复数傅氏变换和超复数互相关的快速方法,然后通过把超复数按实部和各个虚部展开,分别进行传统的快速傅氏变换,再把对应的单位虚向量还原,从而为超复数傅氏变换和超复数互相关提出了一种新的快速算法.分析表明:本文提出的方法比目前现有的方法更简单易行,且计算量更小.最后,本文介绍了我们把超复数互相关技术应用到彩色目标跟踪上获得的一些新结果.     

Image processing through a two-component model

A non-linear space-variant operator is proposed, in order to separate the two additive components of an image: the background which includes the main transitions of the scene and the difference signal which contains details and texture information of the picture. This image model turns out to be a quite useful in most picture processing applications and it is consistent with visual perception constraints. In particular, restoration in separately performed on the two image components, since linear degradations mainly affect the background while the details are highly corrupted by noise. The examples included demonstrate the usefulness of this approach.     

Rotation Invariance in 2D-FRFT with Application to Digital Image Watermarking

The extraction of rotation invariant representation is important for many signal processing tasks such as image analysis, computer vision, pattern recognition and so forth. In this paper, we show that, under certain conditions, the Two-Dimensional Fractional Fourier Transform (2D-FRFT) possesses this attractive property through mathematical analysis and extensive computer simulations. Based on this property, we propose a novel digital image watermarking method which combines 2D chirp signal with the addition and rotation invariant properties of 2D-FRFT in order to improve robustness and security of digital image watermark in 2D-FRFT domain. Experimental results show that the proposed method is robust against numerous watermarking attacks including rotation geometrical transform, JPEG compression, crop, median filtering, histogram equalization, salt & pepper noise, Gaussian lowpass filter, shift, dithering and Gaussian noise, and secures against unauthorized information copying and redistribution.     

Rotation, scale, and translation resilient watermarking for images

Many electronic watermarks for still images and video content are sensitive to geometric distortions. For example, simple rotation, scaling, and/or translation (RST) of an image can prevent blind detection of a public watermark. In this paper, we propose a watermarking algorithm that is robust to RST distortions. The watermark is embedded into a one-dimensional (1-D) signal obtained by taking the Fourier transform of the image, resampling the Fourier magnitudes into log-polar coordinates, and then summing a function of those magnitudes along the log-radius axis. Rotation of the image results in a cyclical shift of the extracted signal. Scaling of the image results in amplification of the extracted signal, and translation of the image has no effect on the extracted signal. We can therefore compensate for rotation with a simple search, and compensate for scaling by using the correlation coefficient as the detection measure. False positive results on a database of 10 000 images are reported. Robustness results on a database of 2000 images are described. It is shown that the watermark is robust to rotation, scale, and translation. In addition, we describe tests examining the watermarks resistance to cropping and JPEG compression.