Protecting portable devices is becoming more important, not only because of the value of the devices themselves, but for the value of the data in them and their capability for transactions, including m-commerce and m-banking. An unobtrusive and natural method for identifying the carrier of portable devices is presented. The method uses acceleration signals produced by sensors embedded in the portable device. When the user carries the device, the acceleration signal is compared with the stored template signal. The method consists of finding individual steps, normalizing and averaging them, aligning them with the template and computing cross-correlation, which is used as a measure of similarity. Equal Error Rate of 6.4% is achieved in tentative experiments with 36 test subjects.
Typical surface inspection tasks using RGB vision require the analysis of tens of megabytes of image data per second, with low false alarm and error escape rates. Although automatic inspection systems have become more common on production lines, for example in sawmills, there are substantial needs to improve their performance and accuracy. Detection is one very important part of image flow before defect recognition. Detection is used in order to find suspicious regions of the image, containing possibly defective areas, since defect detection has to cope with very high data rates. It has to be based on relative simple methods. In this paper we describe the effect of different thresholding methods in RGB defect detection. Threshold values were calculated for R, G and B channels, difference channels R-G, R-B and G- B and for mean values from R, G and B channels. The analysis was performed for pinewood. Error escape rate and false alarm rates were used as evaluation criteria. In this paper, R and G channel thresholding methods were the best ones.
In this research characteristics of standard commercial CCD and CMOS cameras are evaluated experimentally and compared. Special attention is paid to the operation of these devices in low light level condition, which is typical to many surveillance and consumer electronics applications. One emerging application utilizing inexpensive image sensors at variable illumination condition is the UMTS (Universal Mobile Telecommunications System), which will deliver wirelessly, for example, pictures, graphics and video from the year 2002. The determination of the system performance is based in this study on the imaging of a calibrated gray scale test chart at varying illumination condition. At each level of illumination the system response is characterized by a signal to random noise figure. The signal is calculated as the difference of the system response to the lightest and darkest areas of the gray scale. The random noise is measured as the standard deviation of the gray values in a difference of two successive images of the test pattern. The standard deviation is calculated from 10-bit digitized images for small group of pixels (36 X 36) corresponding to the different areas of the gray scale in the test pattern images. If the random noise is plot as a function of signal (encoded in digital numbers, DN) for small group of pixels, a Photon Transfer curve is obtained. This is one of the basic performance standards of CCD sensors. However, if camera systems with nonlinear response or AGC are evaluated, the variations of the system response at different signal levels should be included to the performance measure. In these cases the signal to noise curve is useful. The signal to random noise curves were determined for a CCD and a CMOS camera characterized by similar specifications. The comparison between two camera systems shows that considerable differences between the operation of these devices especially at low light level condition can exist. It was found that approximately a sevenfold illumination level is needed in the case of the exemplary CMOS camera compared to the CCD camera in order to achieve a reasonable imaging performance.
This paper presents an experimental system for machine vision guided waterjet cutting. Machine vision is used to provide accurate real-time data on the outline and position of the preform utilised in the nesting process, leading to material and cost savings. The experimental system comprises a computer-controlled waterjet cutting system, a machine vision system and a CAD system. Three 5000-pixel linescan cameras are employed in the vision system, providing a spatial resolution of 0.2 mm over the 3 m wide table. Image analysis software, height correction and calibration methods have been developed for the application, and these have been tested under real conditions.
In this paper we present a novel system concept for large scale flatness and dimensional measurement applications. This system has several advantages over traditional projection moire systems. The system has a robust optomechanical structure which avoids the tight mounting tolerances seen in current projection moire implementations. This means that the system concept will be more applicable to installations in a hostile production environment, at lower cost. The system can be installed close to the object under measurement and produces a good quality moire signal on variable surfaces including impurities, texture, markings, etc. The competitiveness of the flatness measurement system is increased by building a multipurpose system and adding such measurements as edges, width or surface quality to the same unit.
There is clear need for integrated and affordable machine vision systems in line-scan applications, e.g. for width measurement and defect detection. These applications require sensor-like solutions in a price range not achievable with traditional machine vision systems consisting of a line-scan camera, host computer, frame grabber and possibly one or more dedicated processing boards. Since an integrated solution would make a separate host computer and associated boards unnecessary, we set out to study the feasibility of integrated machine vision technology for such applications. Analyses of several potential applications were used to define the requirements for an integrated line-scan camera-based vision system. In order to demonstrate the feasibility of the concept, research prototype was designed based on these requirements. This is a complete machine vision system with camera front end, fast hardware for corrections, the necessary logic and a computer for higher-level data analysis and I/O. A 4096-pixel CCD array followed by 20 MHz 10 A/D conversion forms the front end. Illumination correction, geometric correction, 7 by 7 convolution, multilevel pixelwise thresholding and histogramming are all implemented with fast erasable programmable logic device (EPLD) circuits. A compact PC/104 with a 486 processor takes care of the high-level processing and control. Communication facilities include 12 TTL-level I/O lines, a serial line and a video output.
A variety of time delay and integration (TDI) arrays have been developed. The TDI image sensor offers significant improvement in performance over a linear CCD-sensor with respect to sensitivity. This is particularly significant in low light level operation since the effective exposure time is increased by a factor which is equal to the number of the TDI stages in the sensor. Our previous work has indicated that the TDI camera can be used with viewing angles up to 30 degrees from the surface normal. The effects caused by vibration of the viewed surface become critical when using a TDI camera at non-zero viewing angles.FOr this reason, a study was made on the vibration effects. This paper reports this study, concentrating ont he relation between the vibration of the inspected surface and the sharpness of the image. The contrast perceived by the TDI camera as a function of the vibration amplitude and frequency is measured. The measurements are performed using a special test pattern in a dynamic situation. The results based on the contrast modulation function (CMF) in the vertical and horizontal directions are reported. A hypothesis of the effect of vibration on the CMF was formulated as a rule, which was then tested with measured data. Tentative result support the hypothesis.
A variety of time delay and integration (TDI) arrays have been developed. The TDI image sensor offers significant improvement in performance over a linear CCD-sensor with respect to sensitivity. This is particularly significant in low level operations since the exposure time is increased by a factor which is equal to the number of the TDI stages in the sensor. Typically, the use of a TDI camera is restricted to cases where the surface is viewed from the direction of the surface normal. This is because the TDI-camera sensor has to be parallel to the viewed surface plane, in order to avoid a decrease of image quality due to varying magnification. However, in certain visual inspection applications it would be advantageous to use non-zero viewing angles. Three different solutions were tested and analyzes: a commercial shifting lens, standard lenses with an extension structure to support the lens in the shifting position and a commercial shifting and tilting lens. The results indicate that the TDI-camera can be used with viewing angles up to 30 degrees from the surface normal,which has been found to be the optimal viewing angle in some visual inspection applications.
A laser rangefinder-based optical coordinate measurement system used for monitoring refractory lining wear in steel mills has been equipped with a vision system to improve its operative and performance characteristics. The 3D shape of the refractory lining is measured after renewal at the beginning of a campaign and these data are stored as a reference. During the campaign the lining is measured and the results are compared against the reference data in order to minimize risks and optimize lining life. To make the results measured at different times comparable, they must be accurately and reliably transformed to the same coordinate system. This makes the coordinate system setup phase critical for the success of the lining wear monitoring. Other important aspects are the amount of expensive process time taken up by the measurements and work safety aspects. The experimental vision system has been tesetd for automating the corrdinate system setup phase, and improved repeatability and faster operation compared with manual setup was achieved. Tentative tests at a steel mill proved promising, and further development of the vision system is going on.
An experimental measurement system for dimensional quality control is described in which laser radar based 3D coordinate measurements are guided to given points using information from video imagery. The system is controlled by a measurement model file that contains the measurement program and the nominal data of the interesting features in the target object. Because the real world objects differ from the nominal model due to, e.g., changes in their shape, dimensions and position, the measurement system must be adaptive. This adaptivity is provided by using video imagery for guiding the 3D coordinate measurements to the position indicated in the measurement program. At the moment the system is capable of finding points that are marked with circular tags and guiding the laser range finder beam into these points. The linearity and repeatability of the image analysis based feature finding system is better than 0.5 mm at 11 m. Tag finding in a 512 by 574 image takes ca. 2.5 second using a low cost frame grabber and a PC.
3-b vision c be employed in the inspection of geometric properties i. e. the shape and dimensions of industrial objects A method for the inspection of the 3-D shape of a c1as of industrial objects is presented in this paper. The method compares the CAD model of th bbject with information processed from a dense range map. Tentative test results are shown and their implications discussed. We suggest that preplanning the measurement and analysis stage and use of a programmable 3D sensor instead of a dumb camera-type sensor would give better performance.