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1.
This paper describes a method for recognizing partially occluded objects under different levels of illumination brightness
by using the eigenspace analysis. In our previous work, we developed the “eigenwindow” method to recognize the partially occluded
objects in an assembly task, and demonstrated with sufficient high performance for the industrial use that the method works
successfully for multiple objects with specularity under constant illumination. In this paper, we modify the eigenwindow method
for recognizing objects under different illumination conditions, as is sometimes the case in manufacturing environments, by
using additional color information. In the proposed method, a measured color in the RGB color space is transformed into one
in the HSV color space. Then, the hue of the measured color, which is invariant to change in illumination brightness and direction,
is used for recognizing multiple objects under different illumination conditions. The proposed method was applied to real
images of multiple objects under various illumination conditions, and the objects were recognized and localized successfully. 相似文献
2.
Machine vision system for curved surface inspection 总被引:2,自引:0,他引:2
Min-Fan Ricky Lee Clarence W. de Silva Elizabeth A. Croft Q.M. Jonathan Wu 《Machine Vision and Applications》2000,12(4):177-188
This application-oriented paper discusses a non-contact 3D range data measurement system to improve the performance of the
existing 2D herring roe grading system. The existing system uses a single CCD camera with unstructured halogen lighting to
acquire and analyze the shape of the 2D shape of the herring roe for size and deformity grading. Our system will act as an
additional system module, which can be integrated into the existing 2D grading system, providing the additional third dimension
to detect deformities in the herring roe, which were not detected in the 2D analysis. Furthermore, the additional surface
depth data will increase the accuracy of the weight information used in the existing grading system. In the proposed system,
multiple laser light stripes are projected into the herring roe and the single B/W CCD camera records the image of the scene.
The distortion in the projected line pattern is due to the surface curvature and orientation. Utilizing the linear relation
between the projected line distortion and surface depth, the range data was recovered from a single camera image.
The measurement technique is described and the depth information is obtained through four steps: (1) image capture, (2) stripe
extraction, (3) stripe coding, (4) triangulation, and system calibration. Then, this depth information can be converted into
the curvature and orientation of the shape for deformity inspection, and also used for the weight estimation.
Preliminary results are included to show the feasibility and performance of our measurement technique. The accuracy and reliability
of the computerized herring roe grading system can be greatly improved by integrating this system into existing system in
the future. 相似文献
3.
在多视点图像系统中,由于场景光照或相机标定的原因,通常会导致同一对象在不同视点位置颜色外表的不一致。传统的亮度补偿算法难以有效地解决这个问题。基于Retinex颜色恒常性理论,提出了一种新颖的多视点图像规正算法,通过直方图均衡化、Retinex处理和颜色恢复手段,提取出反映物体本质特征的反射光系数来消除不一致光照的影响,在增强单视点图像对比度的同时,将视点间图像的颜色规正到一致的水平。 相似文献
4.
Is it possible to calibrate a camera in the air and then use the calibration results to infer a new calibration corresponding
to the embedding of the camera in another fluid (possibly water)? This problem is dealt within the paper. It is important
to avoid direct underwater calibration, as it is much more inconvenient for experiments than the usual (air) calibration by
human workers. Optical laws that must be considered when using underwater cameras are investigated. Both theoretical and experimental
point of views are described, and it is shown that relationships can be found between results of air and water (or any other
isotropic fluid in which the camera can be submerged) calibration.
Received: 22 April 2000 / Accepted: 13 May 2002
Correspondence to: J.M. Lavest 相似文献
5.
对于在可见光范围拍摄的图像中混入近红外光引起的图像偏色问题,传统监控系统采用机械切换的红外截止滤镜来实现日夜拍摄模式的切换,但这容易产生机械故障,影响成像.本文在不改变原来CCD或CMOS传感器的基础上,采用可见光加850 nm双峰滤镜替代传统机械切换滤镜,但仍存在850 nm红外串扰问题.为解决红外干扰,本文抛弃传统的红外干扰图像偏色校正分析方法,从传感器受近红外光的影响分析入手,通过岭回归的彩色定标方法对相机自身的光谱特性进行校正.这个过程即拟合了摄像头拍摄三带图像时启用红外截止滤镜的状态.首先在实验室黑暗环境中,使用D65标准光源箱,并用850 nm的近红外光源直射已经移除红外截止滤镜的摄像头,在棚中拍摄潘通色卡的四带图像(RGB三带与IR近红外带);随后关闭近红外光源,同机位拍摄潘通色卡的三带图像.根据岭回归算法进行彩色定标,获取三带图像与四带图像之间的校正矩阵,用于四带图像色彩校正,获得色彩自然的图像. 相似文献
6.
Straight lines have to be straight 总被引:18,自引:0,他引:18
Most algorithms in 3D computer vision rely on the pinhole camera model because of its simplicity, whereas video optics, especially
low-cost wide-angle or fish-eye lenses, generate a lot of non-linear distortion which can be critical. To find the distortion
parameters of a camera, we use the following fundamental property: a camera follows the pinhole model if and only if the projection
of every line in space onto the camera is a line. Consequently, if we find the transformation on the video image so that every
line in space is viewed in the transformed image as a line, then we know how to remove the distortion from the image. The
algorithm consists of first doing edge extraction on a possibly distorted video sequence, then doing polygonal approximation
with a large tolerance on these edges to extract possible lines from the sequence, and then finding the parameters of our
distortion model that best transform these edges to segments. Results are presented on real video images, compared with distortion
calibration obtained by a full camera calibration method which uses a calibration grid.
Received: 27 December 1999 / Accepted: 8 November 2000 相似文献
7.
Abstract. Image feedback path tracking (IFPT) control of a laser light point (LLP) using a CCD camera is studied in this paper. The
tracking path and the LLP are assumed clearly focused in the scene, but no camera calibration is needed. A modified version
of the thinning algorithm SPTA is proposed to skeletonize the path in a piecewise manner. The proposed thinning algorithm
takes less computer time than the original SPTA and makes the real-time skeletonization possible. Included in the paper is
also the development of a control algorithm with image feedback to assure LLP tracking along the required path, as well as
an experimental study to demonstrate how IFPT control can be realized in practice.
Received: 10 November 1999 / Accepted: 9 March 2000 相似文献
8.
Wood inspection with non-supervised clustering 总被引:9,自引:0,他引:9
Abstract. The appearance of sawn timber has huge natural variations that the human inspector easily compensates for mentally when determining
the types of defects and the grade of each board. However, for automatic wood inspection systems these variations are a major
source for complication. This makes it difficult to use textbook methodologies for visual inspection. These methodologies
generally aim at systems that are trained in a supervised manner with samples of defects and good material, but selecting
and labeling the samples is an error-prone process that limits the accuracy that can be achieved. We present a non-supervised
clustering-based approach for detecting and recognizing defects in lumber boards. A key idea is to employ a self-organizing
map (SOM) for discriminating between sound wood and defects. Human involvement needed for training is minimal. The approach
has been tested with color images of lumber boards, and the achieved false detection and error escape rates are low. The approach
also provides a self-intuitive visual user interface.
Received: 16 December 2000 / Accepted: 8 December 2001
Correspondence to: O. Silvén 相似文献
9.
Using vanishing points for camera calibration and coarse 3D reconstruction from a single image 总被引:5,自引:0,他引:5
In this paper, we show how to calibrate a camera and to recover the geometry and the photometry (textures) of objects from
a single image. The aim of this work is to make it possible walkthrough and augment reality in a 3D model reconstructed from
a single image. The calibration step does not need any calibration target and makes only four assumptions: (1) the single
image contains at least two vanishing points, (2) the length (in 3D space) of one line segment (for determining the translation
vector) in the image is known, (3) the principle point is the center of the image, and (4) the aspect ratio is fixed by the
user. Each vanishing point is determined from a set of parallel lines. These vanishing points help determine a 3D world coordinate
system R
o. After having computed the focal length, the rotation matrix and the translation vector are evaluated in turn for describing
the rigid motion between R
o and the camera coordinate system R
c. Next, the reconstruction step consists in placing, rotating, scaling, and translating a rectangular 3D box that must fit
at best with the potential objects within the scene as seen through the single image. With each face of a rectangular box,
a texture that may contain holes due to invisible parts of certain objects is assigned. We show how the textures are extracted
and how these holes are located and filled. Our method has been applied to various real images (pictures scanned from books,
photographs) and synthetic images. 相似文献
10.
Algorithms for coplanar camera calibration 总被引:5,自引:0,他引:5
Abstract. Coplanar camera calibration is the process of determining the extrinsic and intrinsic camera parameters from a given set
of image and world points, when the world points lie on a two-dimensional plane. Noncoplanar calibration, on the other hand,
involves world points that do not lie on a plane. While optimal solutions for both the camera-calibration procedures can be
obtained by solving a set of constrained nonlinear optimization problems, there are significant structural differences between
the two formulations. We investigate the computational and algorithmic implications of such underlying differences, and provide
a set of efficient algorithms that are specifically tailored for the coplanar case. More specifically, we offer the following:
(1) four algorithms for coplanar calibration that use linear or iterative linear methods to solve the underlying nonlinear
optimization problem, and produce sub-optimal solutions. These algorithms are motivated by their computational efficiency
and are useful for real-time low-cost systems. (2) Two optimal solutions for coplanar calibration, including one novel nonlinear
algorithm. A constraint for the optimal estimation of extrinsic parameters is also given. (3) A Lyapunov type convergence
analysis for the new nonlinear algorithm. We test the validity and performance of the calibration procedures with both synthetic
and real images. The results consistently show significant improvements over less complete camera models.
Received: 30 September 1998 / Accepted: 12 January 2000 相似文献
11.
REFLICS: Real-time flow imaging and classification system 总被引:1,自引:0,他引:1
Sadahiro Iwamoto David M. Checkley Jr. Mohan M. Trivedi 《Machine Vision and Applications》2001,13(1):1-13
An accurate analysis of a large dynamic system like our oceans requires spatially fine and temporally matched data collection
methods. Current methods to estimate fish stock size from pelagic (marine) fish egg abundance by using ships to take point
samples of fish eggs have large margins of error due to spatial and temporal undersampling. The real-time flow imaging and
classification system (REFLICS) enhances fish egg sampling by obtaining continuous, accurate information on fish egg abundance
as the ship cruises along in the area of interest. REFLICS images the dynamic flow with a progressive-scan area camera (60
frames/s) and a synchronized strobe in backlighting configuration. Digitization and processing occur on a dual-processor Pentium
II PC and a pipeline-based image-processing board. REFLICS uses a segmentation algorithm to locate fish-egg-like objects in
the image and then a classifier to determine fish egg, species, and development stage (age). We present an integrated system
design of REFLICS and performance results. REFLICS can perform in real time (60 Hz), classify fish eggs with low false negative
rates on real data collected from a cruise, and work in harsh conditions aboard ships at sea. REFLICS enables cost-effective,
real-time assessment of pelagic fish eggs for research and management.
Received: 12 April 2000 / Accepted: 6 July 2000 相似文献
12.
Password hardening based on keystroke dynamics 总被引:2,自引:0,他引:2
Fabian Monrose Michael K. Reiter Susanne Wetzel 《International Journal of Information Security》2002,1(2):69-83
We present a novel approach to improving the security of passwords. In our approach, the legitimate user’s typing patterns
(e.g., durations of keystrokes and latencies between keystrokes) are combined with the user’s password to generate a hardened password that is convincingly more secure than conventional passwords alone. In addition, our scheme automatically adapts to gradual
changes in a user’s typing patterns while maintaining the same hardened password across multiple logins, for use in file encryption
or other applications requiring a long-term secret key. Using empirical data and a prototype implementation of our scheme,
we give evidence that our approach is viable in practice, in terms of ease of use, improved security, and performance.
Published online: 26 October 2001 相似文献
13.
angular velocity control dynamic system guides the agent's direction angle, while another dynamic system selects the environmental input that will
be used in the control system. The agent interacts with the environment through its knowledge of the position of stationary
and moving objects. In our system agents automatically avoid stationary and moving obstacles to reach the desired target(s).
This approach allows us to prove the stability conditions that result in a principled methodology for the computation of the
system's dynamic parameters. We present a variety of real-time simulations that illustrate the power of our approach. 相似文献
14.
Traditional digital particle image velocimetry (DPIV) methods are previously based on area-correlation. Though proven to
be very time-consuming and error prone, it has been widely adopted because it is conceptually simple, and easy to implement,
and also because there are few alternatives. This paper provides a non-correlative, conceptually new, fast and efficient approach
for DPIV which takes the nature of flow into consideration. An incompressible affine flow model (IAFM) is introduced to describe a flow that incorporates rational constraint directly into the computation. This IAFM, combining
with a modified optical flow method – named total optical flow computation, provides a linear system solution to DPIV. Experimental results on real images demonstrate our method to be a very promising
approach for DPIV.
Received: 23 March 1998 / Accepted: 1 September 1999 相似文献
15.
Real-time multiple vehicle detection and tracking from a moving vehicle 总被引:18,自引:0,他引:18
Abstract. A real-time vision system has been developed that analyzes color videos taken from a forward-looking video camera in a car
driving on a highway. The system uses a combination of color, edge, and motion information to recognize and track the road
boundaries, lane markings and other vehicles on the road. Cars are recognized by matching templates that are cropped from
the input data online and by detecting highway scene features and evaluating how they relate to each other. Cars are also
detected by temporal differencing and by tracking motion parameters that are typical for cars. The system recognizes and tracks
road boundaries and lane markings using a recursive least-squares filter. Experimental results demonstrate robust, real-time
car detection and tracking over thousands of image frames. The data includes video taken under difficult visibility conditions.
Received: 1 September 1998 / Accepted: 22 February 2000 相似文献
16.
Transporting QoS adaptive flows 总被引:4,自引:0,他引:4
Distributed audio and video applications need to adapt to fluctuations in delivered quality of service (QoS). By trading
off temporal and spatial quality to available bandwidth, or manipulating the playout time of continuous media in response
to variation in delay, audio and video flows can be made to adapt to fluctuating QoS with minimal perceptual distortion. In
this paper, we extend our previous work on a QoS Architecture (QoS-A) by populating the QoS management planes of our architecture
with a framework for the control and management of multilayer coded flows operating in heterogeneous multimedia networking
environments. Two key techniques are proposed: i) an end-to-end rate-shaping scheme which adapts the rate of MPEG-coded flows
to the available network resources while minimizing the distortion observed at the receiver; and ii) an adaptive network service,
which offers “hard” guarantees to the base layer of multilayer coded flows and “fairness” guarantees to the enhancement layers
based on a bandwidth allocation technique called Weighted Fair Sharing. 相似文献
17.
Automatic high-resolution optoelectronic photogrammetric 3D surface geometry acquisition system 总被引:1,自引:0,他引:1
A fast, high-resolution, automatic, non-contact 3D surface geometry measuring system using a photogrammetric optoelectronic
technique based on lateral-photoeffect diode detectors has been developed. Designed for the acquisition of surface geometries
such as machined surfaces, biological surfaces, and deformed parts, the system can be used in design, manufacturing, inspection,
and range finding. A laser beam is focused and scanned onto the surface of the object to be measured. Two cameras in stereo
positions capture the reflected light from the surface at 10 kHz. Photogrammetric triangulation quickly transforms the pair
of 2D signals created by the camera detectors into 3D coordinates of the light spot. Because only one small spot on the object
is illuminated at a time, the stereo correspondence problem is solved in real time. The resolution is determined by a 12-bit
A/D converter and can be improved up to 25 60025 600 by oversampling. The irregular 3D data can be regularized for use with image-based algorithms.
Received: 8 October 1996 / Accepted: 3 February 1997 相似文献
18.
In video processing, a common first step is to segment the videos into physical units, generally called shots. A shot is a video segment that consists of one continuous action. In general, these physical units need to be clustered
to form more semantically significant units, such as scenes, sequences, programs, etc. This is the so-called story-based video
structuring. Automatic video structuring is of great importance for video browsing and retrieval. The shots or scenes are
usually described by one or several representative frames, called key-frames. Viewed from a higher level, key frames of some shots might be redundant in terms of semantics. In this paper, we propose
automatic solutions to the problems of: (i) video partitioning, (ii) key frame computing, (iii) key frame pruning. For the
first problem, an algorithm called “net comparison” is devised. It is accurate and fast because it uses both statistical and
spatial information in an image and does not have to process the entire image. For the last two problems, we develop an original
image similarity criterion, which considers both spatial layout and detail content in an image. For this purpose, coefficients
of wavelet decomposition are used to derive parameter vectors accounting for the above two aspects. The parameters exhibit
(quasi-) invariant properties, thus making the algorithm robust for many types of object/camera motions and scaling variances.
The novel “seek and spread” strategy used in key frame computing allows us to obtain a large representative range for the
key frames. Inter-shot redundancy of the key-frames is suppressed using the same image similarity measure. Experimental results
demonstrate the effectiveness and efficiency of our techniques. 相似文献
19.
In this paper, we discuss an appearance-matching approach to the difficult problem of interpreting color scenes containing
occluded objects. We have explored the use of an iterative, coarse-to-fine sum-squared-error method that uses information
from hypothesized occlusion events to perform run-time modification of scene-to-template similarity measures. These adjustments
are performed by using a binary mask to adaptively exclude regions of the template image from the squared-error computation.
At each iteration higher resolution scene data as well as information derived from the occluding interactions between multiple
object hypotheses are used to adjust these masks. We present results which demonstrate that such a technique is reasonably
robust over a large database of color test scenes containing objects at a variety of scales, and tolerates minor 3D object
rotations and global illumination variations.
Received: 21 November 1996 / Accepted: 14 October 1997 相似文献
20.
In this paper, we systematically assess the performance of an automatic calibration chart detector. Through simulation we
establish the optimal set of control parameters and the rate of successful detection as a function of pose. We validate the
simulation results on real images taken from a camera mounted on a robot arm. The results confirm the utility of such simulation
studies. The feedback obtained suggested a number of modifications for the chart detection system, which led to a significant
improvement in performance. In particular, the chart design was changed to accommodate wider range and better stability in
detection.
Received: 16 December 1999 / Accepted: 15 October 2000 相似文献