Sensitivity of landscape metrics to pixel size

Analysis of diversity and evenness metrics using land cover data are becoming formalized in landscape ecology. Diversity and evenness metrics are dependent on the pixel size (scale) over which the data are collected. Aerial photography was interpreted for land cover and converted into four raster data sets with 4, 12, 28, and 80m pixel sizes, representing pixel sizes up to that available on Landsat-MSS. Analysis of covariance was used to determine the effect of changing pixel size on landscape metrics. The results indicate that landscape metrics should not be dramatically affected by the change in pixel size up to 80m, provided that identical land cover classifications could be generated by sensors with different spatial resolving powers (e.g. Landsat-TM and MSS).     

大尺寸像素电荷转移的优化方法

为了提高CMOS图像传感器大尺寸像素的电荷转移效率,消除图像拖尾,通过对像素内电荷转移的RC模型分析,提出一种优化电荷转移的方法。从工艺和版图两方面进行优化,工艺方面是在N埋层的形成步骤中增加一步P型杂质注入,使光电二极管内存在电场,增强电荷转移;版图方面是优化光电二极管的版图为U型,使传输栅伸进光电二极管内尽量长,减少RC模型的传输级数,提高电荷转移效率。与传统像素相比,工艺和版图的优化使电荷转移效率分别提高了2倍和3.3倍,转移时间也分别缩短到传统像素结构的26%和30%左右。对传统像素结构进行工艺和版图同时优化则使电荷转移效率提高了9.5倍。     

Finding the right ATM switch for the market

The asynchronous transfer mode (ATM) promises to be the ultimate on-premise internetworking technology. Its high-bandwidth uniform switches can transfer graphics, audio, video. and text from application to application at much higher speeds than now available. In fact, ATM may well be the technology that brings the computer and communications industries together. Because ATM as a public service offering by telecommunications companies will probably not be in place before 1996-1997, the authors focus on the ATM LAN and the corporate backbone. Most of the proposals on the internal architecture of the ATM switch are still at a research-and-evaluation stage, based on the switching architectures of the 1970s and 198Os. Various objectives, such as blocking, routing, performance and VLSI implementation, motivated past work. Although these attributes are essential, they don't address concerns important to the commercial ATM market, such as the general cost of ownership and incremental deployment, scalability, reliability, and efficient bandwidth utilization. The few ATM switches on the market today embody attributes that meet current demands but must evolve to meet the future. The authors assess the architectural characteristics deemed necessary for the ATM switch, providing an overview of its purpose and protocols, and summarize key ATM switch proposals. They summarize commercial market requirements and profile several commercially available systems to show the current gap between the research community and the commercial market, providing a model for the future     

Finding the right data for software cost modeling

Good software cost models can significantly help software project managers. With good models, project stakeholders can make informed decisions about how to manage resources, how to control and plan the project, or how to deliver the project on time, on schedule, and on budget. Real-world data sets, such as those coming from software engineering projects, often contain noisy, irrelevant, or redundant variables. We propose that cost modelers should perform data-pruning experiments after data collection and before model building. Such pruning experiments are simple and fast.     

Impact of pixel size on mapping surface water in subsolar imagery

We observed surface water in a wetland, imaging in the subsolar or specular direction the exceptionally bright specular reflection of sunlight at a ground resolution of 0.3 m. We then simulated ground resolutions between 1.7 m and 1.2 km through aggregation of the 0.3 m pixels. Contrary to the expectations of some of our colleagues in the wetlands community, for these data, the accuracy of spectral mixture analysis (SMA) estimates of surface water increases as pixel ground footprint size increases. Our results suggest that regional to global scale assessments of flooded landscapes and wetlands that do not involve issues requiring 1 m resolution per se may be addressed with acceptable accuracy by applying SMA techniques to low resolution imagery. Our results indicate within-pixel estimates of surface water area derived from data measured by subsolar viewing sensors with large ground pixel footprints, such as satellite POLarization and Directionality of Earth Radiance (POLDER) data, may be highly accurate under strong surface wind conditions.     

Optimum pixel size for hyperspectral studies of ecosystem function in southern California chaparral and grassland

Hyperspectral remotely sensed data are useful for studying ecosystem processes and patterns. However, spatial characterization of such remotely sensed images is needed to optimize sampling procedures and address scaling issues. We have investigated spatial scaling in ground-based and airborne hyperspectral data for canopy- to watershed-level ecosystem studies of southern California chaparral and grassland vegetation. Three optical reflectance indices, namely, Normalized Difference Vegetation Index (NDVI), Water Band Index (WBI) and Photochemical Reflectance Index (PRI) were used as indicators of biomass, plant water content and photosynthetic activity, respectively. Two geostatistical procedures, the semivariogram and local variance, were used for the spatial scaling analysis of these indices. The results indicate that a pixel size of 6 m or less would be optimal for studying functional properties of southern California grassland and chaparral ecosystems using hyperspectral remote sensing. These results provide a guide for selecting the spatial resolution of future airborne and satellite-based hyperspectral sensors.     

Local pixel patterns

Computational Visual Media - In this paper, a new class of image texture operators is proposed. We firstly determine that the number of gray levels in each B × B subblock is a fundamental...     

Hierarchical pixel bar charts

Simple presentation graphics are intuitive and easy-to-use, but only show highly aggregated data. Bar charts, for example, only show a rather small number of data values and x-y-plots often have a high degree of overlap. Presentation techniques are often chosen depending on the considered data type, bar charts, for example, are used for categorical data and x-y plots are used for numerical data. We propose a combination of traditional bar charts and x-y-plots, which allows the visualization of large amounts of data with categorical and numerical data. The categorical data dimensions are used for the partitioning into the bars and the numerical data dimensions are used for the ordering arrangement within the bars. The basic idea is to use the pixels within the bars to present the detailed information of the data records. Our so-called pixel bar charts retain the intuitiveness of traditional bar charts while applying the principle of x-y charts within the bars. In many applications, a natural hierarchy is defined on the categorical data dimensions such as time, region, or product type. In hierarchical pixel bar charts, the hierarchy is exploited to split the bars for selected portions of the hierarchy. Our application to a number of real-world e-business and Web services data sets shows the wide applicability and usefulness of our new idea.     

Understanding burn severity sensing in Arctic tundra: exploring vegetation indices,suboptimal assessment timing and the impact of increasing pixel size

Little is known about how satellite imagery can be used to describe burn severity in tundra landscapes. The Anaktuvuk River Fire (ARF) in 2007 burned over 1000 km² of tundra on the North Slope of Alaska, creating a mosaic of small (1 m²) to large (>100 m²) patches that differed in burn severity. The ARF scar provided us with an ideal landscape to determine if a single-date spectral vegetation index can be used once vegetation recovery began and to independently determine how pixel size influences burn severity assessment. We determine and explore the sensitivity of several commonly used vegetation indices to variation in burn severity across the ARF scar and the influence of pixel size on the assessment and classification of tundra burn severity. We conducted field surveys of spectral reflectance at the peak of the first growing season post-fire (extended assessment period) at 18 field sites that ranged from high to low burn severity. In comparing single-date indices, we found that the two-band enhanced vegetation index (EVI2) was highly correlated with normalized burn ratio (NBR) and better distinguished among three burn severity classes than both the NBR and the normalized difference vegetation index (NDVI). We also show clear evidence that shortwave infrared (SWIR) reflectivity does not vary as a function of burn severity. By comparing a Quickbird scene (2.4 m pixels) to simulated 30 and 250 m pixel scenes, we are able to confirm that while the moderate spatial resolution of the Landsat Thematic Mapper (TM) sensor (30 m) is sufficient for mapping tundra burn severity, the coarser resolution of the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor (250 m) is not well matched to the fine scale of spatial heterogeneity in the ARF burn scar.     

What is a pixel?

The total list of processing required to view a pixel includes antialiasing, offset sampling, color space projection, reconstruction filter compensation, compositing, gamma correction, and quantization and dithering. If we look at all these operations we can see a pattern: Almost all of them throw away information. When we filter out high frequencies, quantize intensities into bins, project a continuous color spectrum into three numbers, and represent geometric edges with a single transparency value we can see that an ordinary-hardware pixel, either refreshed on the screen or stored in a file, is simply a bad data compression technique. Any rendering algorithm or image processing operation that converts data to pixels generally loses information about the original data that it uses as input. A few polygons become thousands of pixels; a high-resolution image becomes a low-resolution image. Conversion to pixels for viewing purposes used to be a slow operation, but with faster processors we no longer need to do the image generation offline for speed purposes. We can recalculate the image whenever we need to look at it.     

动态单像素模板算法

高斯模板用于图像旋转时会产生较严重的模糊,其原因是大邻域的亮度值加权平均造成的。为减小加权平均的邻域范围,提出图像空域变换的小邻域局部相关性原理。据此提出动态单像素模板算法：将当前像素分割为3×3的子像素,对每一个子像素求得一个模板。用当前像素的这9个模板之一和邻域像素的亮度进行卷积运算求得变换后的亮度值。实验和分析表明,它消除了高斯模板旋转图像时产生模糊的问题。旋转图像的质量与双线性插值算法相近,同时具有比双线性插值算法和高斯模板算法更高的计算性能。     

Image segmentation by pixel classification

A fast boundary finding algorithm is presented which works without threshold operation and without any interactive control. The procedure can be described as a hierarchical two-step algorithm. In the first step the image is divided into two disjunct regions, one of them including the whole object of interest.In the second step the problem of boundary finding is suggested as a classification problem, which means that for any pixel a four-dimensional feature vector is computed which allows classification of pixels into contour elements and any other pixels.The algorithm was tested on several thousand cell images and can be easily adapted to other problems by modification of a set of parameters.     

四管像素满阱容量影响因素研究

在分析光电二极管电容、浮空节点电容以及电荷转移效果这三方面影响满阱容量的基础上,着重讨论了最重要的光电二极管电容对满阱容量的影响,建立了满阱容量的计算模型。将测试结果与模型公式进行拟合,可以预估像素的满阱容量,指导像素设计。为了提高四管像素的满阱容量,提出在钳位光电二极管与浮空节点之间增加P型注入层稳定阱容量的方法。增加P型注入层可以大幅减小积分时间内光电二极管中储存的光生电子向浮空节点方向的泄漏,从而有效稳定阱容量。测试结果表明,在多种工艺条件下,像素的满阱容量从基本可以忽略提升至十万个电子的量级。     

基于像素的椭圆窗口裁剪算法

现有的椭圆窗口裁剪算法需通过求交运算确定裁剪对象,算法复杂,而且只适用于简单图形的裁剪.由于裁剪是计算机图形学中基础算法之一,因此找到一种高效的椭圆窗口裁剪算法具有重要的实际意义.提出了一种基于像素的椭圆窗口裁剪算法,首先采用高效的椭圆算法生成裁剪窗口,然后以窗口作为边界利用扫描线原理确定窗口内像素并输出,完成裁剪过程.该方法无需复杂的求交运算,只需简单的像素读写便可完成裁剪操作,因此裁剪过程简单,执行速度快,算法复杂度低,尤其适合于复杂图形及图像的裁剪处理.     

Bisection approach for pixel labelling problem

This paper formulates pixel labelling as a series of two-category classification. Unlike existing techniques, which assign a determinate label to each pixel, we assign a label set to each pixel and shrink the label set step by step. Determinate labelling is achieved within log₂n (n is size of label set) steps. In each step, we bisect the label set into two subsets and discard the one with higher cost of assigning it to the pixel. Simultaneous labelling of an image is carried out by minimizing an energy function that can be minimized via graph cut algorithm. Based on the bisection approach, we propose a bitwise algorithm for pixel labelling, which set one bit of each pixel's label in each step. We apply the proposed algorithm to stereo matching and image restoration. Experimental results demonstrate that both good performance and high efficiency are achieved.     

A trip down the graphics pipeline: pixel coordinates

A general overview of the classic rendering pipeline is given. An examination of some of the problems that come from the use of transformations in the graphics pipeline is initiated. Exemplary transformations to be used in succeeding articles are derived. It is shown that the obvious way to transform normalized device coordinates to pixel space is wrong. The nature of the pixel space is discussed     

像素聚类改进二进制描述子鲁棒性

目标：本文通过挖掘图像局部区域特征信息,提出了一种鲁棒性更高的二进制描述子。针对BRIEF关于旋转和视角变化鲁棒性差的问题,本文通过图像补丁分层处理、增加关键点图像补丁个数来捕获更多的局部特征信息,对BRIEF描述子改进。方法：首先,根据灰度序列对补丁内所有像素点分类,像素的一个聚类形成了一个亚补丁,然后在每个亚图像补丁上进行类似BRIEF的随机测试。其次,由于原图像补丁大小、尺度大小影响补丁的像素点成分,从而影响像素聚类的效果,所以在原图像关键点周围分割出多个不同大小的图像补丁,或是将原图像补丁根据尺度金字塔确定几个尺度大小不同的补丁,然后再对图像补丁进行分层、测试。所构建的描述子不仅包含了补丁像素的灰度比较信息,而且包含了灰度排序信息和像素群聚信息,提高了描述子的鲁棒性。结果：通过性能对比实验,发现所提的描述子的性能提高了,而且好于对比的浮点描述子。结论：所以挖掘图像补丁的特征信息能提高二进制描述子的鲁棒性。     

Contextual classification of multispectral pixel data

Contextual statistical decision rules for classification of lattice-structured data such as pixels in multispectral imagery are developed. Their recursive implementation is shown to have a strong resemblance to relaxation algorithms. Experimental evaluation of the proposed algorithms demonstrates their effectiveness.     

Discrete camera calibration from pixel streams

We consider the problem of estimating the relative orientation of a number of individual photocells – or pixels – that hold fixed relative positions. The photocells measure the intensity of light traveling on a pencil of lines. We assume that the light-field thus sampled is changing, e.g. as the result of motion of the sensors and use the obtained measurements to estimate the orientations of the photocells.Our approach is based on correlation and information-theory dissimilarity measures. Experiments with real-world data show that the dissimilarity measures are strongly related to the angular separation between the photocells, and the relation can be modeled quantitatively. In particular we show that this model allows to estimate the angular separation from the dissimilarity. Although the resulting estimators are not very accurate, they maintain their performance throughout different visual environments, suggesting that the model encodes a very general property of our visual world. Finally, leveraging this method to estimate angles from signal pairs, we show how distance geometry techniques allow to recover the complete sensor geometry.