一种通过曲线拟合去除图像块效应的算法

基于DCT域的图像处理方法具有广泛的应用,但是由于需要对图像的DCT块单独进行处理,导致块效应的产生。本文提出了一种通过曲线拟合去除彩色图像中块效应的算法。首先获得原始图像与块效应图像的对应亮度点云映射关系,进而用曲线拟合的方法计算出最佳拟合曲线,最后使用拟合曲线对原始图像的亮度进行非线性处理,将处理后的亮度与块效应图像的色度分量进行组合。实验表明本文算法不仅能够能够有效地去除块效应、降低了计算量,而且还能够较好保持原块效应图像的色彩。     

色度在评价增强图像时对传统算法的修正效果

增强图像是指与原始图像相比在清晰度、亮度、色彩、对比度等方面有一定增强的图像.图像增强已被广泛应用,例如很多图像处理软件PS,ACDSee等都能够对图像进行增强.与此同时,也出现了很多图像增强算法.所以,对增强图像的质量评价具有重要意义.传统的图像质量评价算法不能够对增强图像进行精确评价.增强图像与原始图像相比,在色度上存在一定差异.在此基础上,研究了色度在评价增强图像质量时对传统的图像质量评价算法的修正效果.在增强图像数据库中进行的实验证明在评价增强图像质量时,色度能够对传统的图像质量评价算法进行较好的修正.     

色度与亮度特征相融合的彩色人脸识别算法

在存在色度与亮度差异性的条件下,彩色人脸的识别准确度不高,为了提高彩色人脸的识别性能,提出基于色度与亮度特征相融合的彩色人脸识别算法。对采集的原始彩色人脸图像进行色度均衡处理,采用特征提取方法进行人脸的关键特征点定位,提取人脸图像的色度和亮度特征。对提取的特征量根据眼睛和眉毛等关键点的差异性进行信息融合,对提取的眼部区域色度信息进行二值化分离和信息增强处理,提高对彩色人脸图像的特征识别能力,实现彩色人脸识别算法的改进设计。仿真结果表明,采用该方法进行彩色人脸识别的准确识别率较高,抗色度和亮度的局部干扰能力较强。     

色度亮度协同滤波的色调映射算法

针对高动态范围图像显现质量有待提高的问题,本文在色度亮度颜色空间中提出了一种基于协同滤波的色调映射算法.首先将输入的高动态范围图像利用色度亮度颜色空间来提取亮度信息和色度信息,然后分别将色度信息和亮度信息进行分解和重构.使用双边滤波技术对亮度信息分解得到亮度基本层和亮度细节层;根据亮度信息和色度信息大尺度边缘的一致性,...     

一种亮度分区和导向滤波相结合的色调映射算法

针对高动态范围(High Dynamic Range,HDR)图像的动态范围与普通显示设备不匹配的问题,本文提出了一种亮度分区和导向滤波相结合的色调映射算法。首先,通过颜色空间转换将输入的HDR图像转换到CIEL*a*b*空间,得到亮度层和色度层图像,接着对亮度层图像进行对数压缩并分区,对压缩后的各分区亮度图像选取合适γ值进行校正。然后,对于现有映射算法过于强调对图像亮度的处理而忽略色度的问题,本文将压缩后的亮度图像作为引导图像对色度层图像进行导向滤波处理。最后,将处理后的亮度层图像和色度层图像融合得到标准动态范围(Standard Dynamic Range,SDR)图像。通过对比实验表明,本文算法得到的图像在清晰度、信息熵、方差方面较全局映射法、局部映射法和双边滤波法平均提高了94.03%、30.73%和24.23%,说明本文算法在实现高动态图像亮度压缩的同时,更好地实现了对色度和局部细节的处理。     

一种针对彩色图像的泛盲掩密分析方案

基于Farid(2002)年泛盲掩密分析算法对彩色图像检测的局限性,提出了新的泛盲掩密分析算法。该算法利用彩色图像的亮度和色度进行分类特征矢量的选择。通过矢量方向滤波技术(VDF)对图像进行方向化处理,并以滤波前后图像之间的矢量方向相关度为色度的分类特征。该方法大大减少了分类特征的数目,而且克服了Farid算法忽略RGB3个颜色通道间相关性的缺陷。分别利用该算法和Farid的算法对JSteg,F5和EZStego软件掩密后的图像进行检测,比较实验结果表明,对于不同长度的嵌入消息,该算法具有更好的检测性能。     

基于亮度保持的子图像加权对比度增强

本文提出了一种有效的基于亮度保持对比度增强算法.利用BBHE(brightness preserving bi-histogram equalization)算法产生的两个子图像,对两个子图像进行加权求和,从而得到输出图像.同时,根据输入图像以及两个子图像的亮度均值,给出了一种基于亮度保持的权重系数的计算方法.实验结果表明,与其它亮度保持对比度增强算法相比,本文算法能够更准确地保持输入图像的亮度均值以及较好地实现对比度增强.另外,本文算法计算简单,能够满足实时性的要求.     

一种DCT压缩域中基于三维椭圆模型的自适应肤色分割算法

肤色分割是彩色图像人脸检测中常用的算法．本文提出了一种应用于DCT（Discrete Cosine Transfom）压缩域的肤色分割算法．采用三维椭圆模型对肤色在YCbCr空间的聚类进行准确描述．统计表明亮度对肤色在色度平面上的聚类有非线性的影响．为了准确描述这种非线性关系，依据亮度变化采用不同参数的椭圆表示肤色在色度平面上的聚类，形成三维椭圆模型．利用亮度分量的交流系数对上述固定模型的初分割结果进行自适应修正，进一步去除背景噪声．实验结果表明本文提出的算法是一种有效的压缩域肤色分割方法．     

灰度遥感图像去云技术及其质量的分析

为了尽可能地呈现灰度遥感图像的信息,对灰图遥感图像分别用小波变换法、改进型多尺度Retinex算法、同态滤波法进行了图像增强处理,分别采用亮度、对比度、亮度与对比度乘积、图像信息熵和变换后的图像与原始图像相比较的保真度等指标对增强后的图像进行分析。结果表明,以采用多尺度Retinex算法增强后,在亮度平均值附近1倍标准差截断、拉伸后得到的图像亮度、对比度、亮度与对比度乘积最高,图像质量最好;小波变换后得到的图像对比度和信息熵最高,去云效果较好;取参量n=1的同态滤波法增强后得到的图像其保真度最高,与原图像最接近,去云效果一般;改进型多尺度Retinex算法和小波变换分别对乌云和白云去除效果最佳。     

一种彩色视频图像序列的三维小波变换编码方法

该文给出了一种基于三维小波变换的彩色视频图像序列的编码方法。先将彩色视频图像序列的RGB(红绿蓝)色彩表示转换成YCbCr(亮度色度色度)表示,再将表示帧序的t坐标代换成z坐标,可将其看成是三维空间中的体。将其分成子块后,仿照二维图像小波变换的方法,对每个亮度色度分量做三维小波变换。变换后的各亮度色度分量的能量主要集中于低频波段,这些波段对该视频图像序列的视觉效果影响最大。将不同分量的各个不同波段按不同的精度量化并进行熵编码,可以达到去除帧内和帧间冗余,压缩数据的目的。试验表明,使用本方法可以达到较好的压缩效果。此方法较直观,速度也比较快。     

Shadow removal using bilateral filtering

In this paper, we propose a simple but effective shadow removal method using a single input image. We first derive a 2-D intrinsic image from a single RGB camera image based solely on colors, particularly chromaticity. We next present a method to recover a 3-D intrinsic image based on bilateral filtering and the 2-D intrinsic image. The luminance contrast in regions with similar surface reflectance due to geometry and illumination variances is effectively reduced in the derived 3-D intrinsic image, while the contrast in regions with different surface reflectance is preserved. However, the intrinsic image contains incorrect luminance values. To obtain the correct luminance, we decompose the input RGB image and the intrinsic image. Each image is decomposed into a base layer and a detail layer. We obtain a shadow-free image by combining the base layer from the input RGB image and the detail layer from the intrinsic image such that the details of the intrinsic image are transferred to the input RGB image from which the correct luminance values can be obtained. Unlike previous methods, the presented technique is fully automatic and does not require shadow detection.     

Compensation of de-saturation effect in HDR imaging using a real scene adaptation model

The iCAM06, a high dynamic range rendering process, contains chromatic adaptation method based on the CIECAM02 model. The D factor, degree of adaptation, in the chromatic adaptation of the iCAM06 is the function of the adapting luminance level, but it does not consider the visual white point shift according to the variation of luminance level. The iCAM06 acquires a blurred illuminant image. So, each pixel has a different illuminant color. When some of the colors cover the entire image, a de-saturation effect appears around these colors. The simply modified D factor to reduce the de-saturation effect causes unsuitable changes in the degree of adaptation. Therefore, we propose a new method to find the global illuminant information and the D factor for the illuminant in the HDR image rendering process. Comparing the proposed with the conventional method, we confirm that the proposed method provides better illuminant estimation and color representation.     

一种使用灰度梯度提取合成孔径雷达图像灰度边界的方法

在合成孔径雷达数字成像的多级成像和合成孔径雷达图像的许多应用中,往往需要提取合成孔径雷达图像的灰度边界特征。人们对于由可见光或红外成像系统获得的普通图像的灰度边界提取已经进行了很多研究。使用灰度梯度提取普通图像的灰度边界非常有效,得到了广泛的应用.但由于在合成孔径雷达图像中存在严重的相干斑噪声,有人认为使用灰度梯度提取合成孔径雷达图像的灰度边界得不到好的结果。在本文中,我们考虑到合成孔径雷达图像的特性,给出了一种比较理想的提取合成孔径雷达图像的灰度边界的方法。这种方法使用相对平均灰度梯度,并且把检测与跟踪结合起来。     

Vision-based strategy to reduce the perceived color misregistrationof image-capturing devices

One of the common artifacts for three-row charge-coupled device (CCD) desktop scanners is color misregistration between the red, green, and blue layers of an image. This causes both color fringing and blur in the resulting scanned images, which we quantify by linear system theory analysis. Knowing the bandwidth and peak sensitivity asymmetries in the opponent color representation of the visual system, we develop a method to reduce the color misregistration artifact by attempting to capture signals in an approximate opponent color space. To facilitate separate capture of the luminance and chrominance signals, we use a new sensor arrangement. The luminance signal (Y) is captured at the full resolution using one row of the three-row CCD linear arrays. The first chrominance signal is captured on another row with a interleaved half resolution red (R) and half resolution luminance sensor elements and the second chrominance signal is similarly captured on a third row using blue (B) and luminance. Since each luminance and chrominance signal is isolated on a single row and since there is no registration error within a row, color misregistration is theoretically prevented in luminance as well as in the chrominance signals. Simulation shows that the new method does reduce blur and the visibility of color fringing. Because residual luminance and chrominance misregistration may occur we conduct a psychophysical experiment to judge the improvement in the scanned image quality. The experiment shows that this new capture scheme can significantly reduce the perception of misregistration artifacts. Finally, we use an image processing model of the visual system to quantify the visible differences due to misregistration and compare these to the psychophysical results     

三代微光像增强器亮度增益对像质影响的分析

为研究三代微光像增强器亮度增益对像质的影响,提出对不同增益条件下荧光屏输出图像的像质进行对比分析,以提高三代微光像增强器的成像质量。首先,在三代微光像增强器的理论基础上,论证了亮度增益会直接影响像增强器的成像质量。然后,通过图像质量评价的两个重要参数信噪比和分辨力,建立像质评价系统并搭建实验装置。最后,通过实验结果表明,在无月夜天光照度条件下,当亮度增益取得最佳值时,输出图像在视场明亮清晰的同时分辨力由32 lp/mm提升至40.3 lp/mm。证明该研究对夜间环境中,如何通过合理设置亮度增益值使微光夜视仪获得最佳成像质量具有指导意义。     

基于校正系统的LED显示屏亮度均匀性评估方法

LED显示屏均匀性,是显示屏图像质量评价中的一个重要指标。文中首先分析了现有基于亮度测量仪器的均匀性评估方法,指出该方法的不足;在LED显示屏亮度校正系统的基础上,对校正系统测量得到的亮度值进行分析处理,提出了以亮度校正系统为基础的LED显示屏亮度均匀性评估方法。该方法能够快捷、客观、全面地得到LED显示屏亮度数据,可以有效评估LED显示屏亮度均匀性。     

Color contrast enhancement method using steerable pyramid transform

A new method of contrast enhancement based on steerable pyramid transform is presented in this work. The use of steerable filters is motivated by the fact that the images are to be observed by human and therefore it would be better to incorporate some knowledge on the Human Visual System in the design of the image processing tool. Here, the frequency and directional selectivity of the HVS is modeled by the steerable filters. The contrast is amplified using a selective nonlinear function which simulates the nonlinearity response of the HVS to the luminance stimuli. So the basic idea is to enhance the luminance signal irrespective of the two chrominance components using a multidirectional and multiscale decorrelation color transform. Initially the rgb (red, green and blue) color image is converted to lab (luminance and chrominance) color image. Only the luminance component is transformed by the steerable pyramid transform, so that the luminance component is independently decomposed into different scale and orientation sub-bands. The contrast in each sub-band is enhanced using a nonlinear mapping function. Finally the rgb color image is obtained from the enhanced luminance component along with the original chrominance components. The performance of the proposed method is objectively evaluated using spectrum energy analysis and a visibility map based on a perceptual filtering model. The obtained results confirm the efficiency of the method in enhancing subtle details without affecting color balance and without the usual noise amplification and edge ringing effect.     

Tone mapping with contrast preservation and lightness correction in high dynamic range imaging

In real-world environments, the human visual system perceives a wide range of luminance in a scene. However, the full range of tones in a high dynamic range (HDR) scene cannot be displayed on standard display devices due to their low dynamic range (LDR). Therefore, tone mapping is necessary to faithfully display a HDR scene on an LDR display device. Existing tone mapping methods have problems because details and contrast in a scene are not preserved faithfully, and they also distort the colors in a scene. Thus, we propose a tone mapping method for preserving the detail in an HDR scene using a weighted least squares filter, which preserves the global contrast in a scene by using a competitive learning neural network, before applying a tone reproduction operator to preserve the color without shifting the lightness. According to the Helmholtz–Kohlrausch effect, the perception of brightness depends on the lightness, chroma, and hue of a color. For example, the luminance of pixels with specific colors such as red and blue is low in an HDR scene. The proposed method corrects the lightness of pixels according to the color (i.e., lightness, chroma, and hue) of a tone-mapped image. Experimental results with several test sets of images demonstrated that the proposed tone mapping method with contrast preservation and lightness correction is more suitable for dynamic range compression than existing tone mapping methods, while it also preserves the color of a scene in an effective way.     

两种不同类型的滤光片式彩色亮度计性能比较

显示器的色度和亮度可以通过彩色亮度计进行测量。小视场滤光片式彩色亮度计因其低成本在生产线上应用广泛,而近来出现的影像式彩色亮度计虽然也属滤光片式,但是由于其探测器不同而具有大视场,且结构、原理和性能与前者都有差异。量化比较这两类滤光片式彩色亮度计的性能,可以为影像式彩色亮度计的质量评估提供依据。文章分别选取两类滤光片式彩色亮度计中的代表型号,通过进行原理分析和实验验证进行对比分析。结果表明,影像式彩色亮度计的性能不低于小视场滤光片式彩色亮度计。     

多参数亮度值重映射的颜色传递方法

为了提高灰度图像中人眼视觉的情景感知和目标的识别率,提出了多参数亮度值重映射的颜色传递方法,将灰度图像赋予色彩。该方法首先将灰度目标图像和彩色参考图像由RGB颜色空间转换到亮度与色彩分离的YCbCr颜色空间。然后,引入由彩色参考图像和灰度目标图像的列数和亮度共同决定的参数,对彩色参考图像的亮度值进行运算,使彩色参考图像与灰度目标图像具有相同的亮度值动态范围。最后,根据目标像素和它周围的像素存在相关性,进行灰度目标图像与彩色参考图像的像素匹配后,将得到的结果再逆变至可以表示出各种色彩的RGB颜色空间。该颜色传递方法降低了色彩误传现象,提高了颜色传递的准确度并缩短了程序的运行时间。