Abstract: A method of detecting a damaged feature within a structure includes embedding a plurality of thin piezoelectric ceramic sensors on the structure. A first sensor is excited so that the first sensor produces a responsive signal in the structure. The responsive signal is received at a second sensor. The presence or absence in the received responsive signal of at least one predetermined signal characteristic is determined, where the predetermined signal characteristic is related to existence of the damage feature.

Abstract: A test methodology for use in a manufacturing process includes generating a test management matrix having a plurality of selectable test sites. Each test site indicates the optimum level of tests to be exercised on devices used to manufacture a product, such as a personal computer. Each test site is accessed through the intersection of inputs relating to aggregate test levels and quality of components used in the device. The tests identified at a selected test site are exercised to test the device.

Abstract: A wafer edge inspection method and apparatus include a review tool that captures images of the semiconductor wafer. According to various embodiments, the present invention also includes a map of points of interest proximate to the edge of the wafer, automatic image capturing at the points of interest, fake defect locations defining the points of interest, a database in which the images are stored and computer-searchable for detailed defect analysis, a software tool for controlling the method and apparatus and/or context information identifying the points of interest, the inspected wafer and/or the fabrication station/step preceding the inspection.

Abstract: A method and system of evaluating a turbine component comprises obtaining data relating to respective surface conditions at a plurality of different surface locations of the turbine component and calculating the total profile efficiency loss for the turbine component based on the data. Calculating the total profile efficiency of the turbine component may include calculating the local profile efficiency loss percentage for each of the surface conditions at the different surface locations (and/or sub-areas of the different surface locations) and calculating an average of the local profile efficiency loss percentages, each of the local efficiency loss percentages being weighted by respective predetermined weight factors. The turbine component may be a nozzle or a bucket and each of the turbine component's surface locations may be an admission suction surface, an admission pressure surface, a discharge suction surface or a discharge pressure surface.

Abstract: A method and device for performing ultrasonic damage detection in a thin-wall structure using an array of embedded Piezoelectric Wafer Active Sensors (PWAS) for the transmission and reception of guided waves and a signal processing methodology based on the beamforming process. The beamforming signal processing has been adapted to the specifics of guided elastic waves traveling in thin-wall structures.

Abstract: A segmentation method of a frame of image information including a plurality of spaced DNA spot images corresponding to a plurality of DNA spots. The image information includes image intensity level information corresponding to said DNA spots. The frame is stored in a memory device and a set of image information within said frame including a selected set of the DNA spot images is selected. A grid including a plurality of spaced grid points corresponding to said selected DNA spot images is generated, such that each grid point includes position information indicating the position of the grid point within said frame.

Abstract: One embodiment of a method comprises retrieving test data corresponding to test results from a plurality of fuses, each one of the plurality of fuses residing on a different one of a plurality of semiconductor devices and each one of the plurality of fuses having a common location on the semiconductor devices, determining from the test data which of the plurality of fuses are defective fuses, and specifying on an output report the common location of the determined defective fuses when a number of the defective fuses are at least equal to a predefined portion of the plurality of fuses.

Abstract: A method and system for identifying a defect or contamination on a surface of a material. The method and system involves providing a material, such as a semiconductor wafer, using a non-vibrating contact potential difference sensor to scan the wafer, generate contact potential difference data and processing that data to identify a pattern characteristic of the defect or contamination.

Abstract: Analog signals are generated in response to one or more operating parameters of a machine such as vibration and used to provide a log of the operating history of the machine. The analog signals are converted into root mean square (rms) values which are periodically sampled. The sampled signals are sorted into predefined rms value bands. Each occurrence of a signal in an rms value band is used to increment a counter in order to keep track of the number of occurrences of signals in a particular rms value band. The number of accumulated signals in each of the rms value bands provides an indication of the usage and condition of the machine.

Abstract: The present invention is directed to improving the accuracy with which a stationary array sensor provides cross directional measurements by providing an offset compensation to the stationary array sensor using the output of a scanning sensor associated with the manufacturing process. Exemplary embodiments correlate outputs from the stationary sensor array and the scanning array using a data reconciliation process. For example, a practical, real time data reconciliation of measurements from the scanning sensor and measurements from the stationary array sensor is achieved by computing offsets using a bank of Kalman filters to correlate outputs from the two sensors for each measurement zone, wherein each filter possesses a relatively simple computational structure. The Kalman filters can fuse the outputs from the stationary array sensor and the scanning sensor to track, and compensate, drift of the stationary array sensor.

Abstract: A computer-implemented process rates pipe segments in a water distribution system, the water distribution system including pipe segments and hydrants. Information gathered from maintenance tasks and inspections performed on the pipe segments and hydrants within the water distribution system is stored in an electronic database. The information in the electronic database is analyzed for a specified period of time to determine the presence of water quality factors and service interruption factors. Points are assigned to the pipe segments based on the presence of the water quality factors and service interruption factors. The pipe segments are rated based on the total points assigned to the pipe segments. The pipe segment ratings can be used for prioritizing the replacement of pipe segments in the water distribution system.

Abstract: An apparatus and method for detecting a leak in a pipe, the apparatus comprising a sensor (11) located at a pipe (7), configured to detect a signal from the pipe, converter means to convert the signal detected by the sensor into a digital signal, and transform means to transform the digital signal into a different orthogonal space. The apparatus also comprises a transmitter (15) for transmitting the transformed digital signal back to a remote processor.

Abstract: The invention relates to a method for monitoring a process. The image information received from cameras monitoring various positions of the process is stored in digital form and various cameras positions are alternately selected for a display and analysis on the screen of a computer. The screen is also used for displaying an image variation graph representing the image variation data of images preceding and following the image to be analyzed. The system includes selector elements (5) for selecting a camera position representing the highest-level image variation for an automated display.

Abstract: A nondestructive inspection method for composite structures, including thick core structures, is disclosed that imparts a vibration force into the structure and analyzes the response over a range of frequencies to find possible damaged areas. The composite structure is struck to induce vibration at a series of test points and the response of the composite structure as a function of acceleration at each test point is measured. The structural anomalies in the composite structure occur at structural stiffness irregularities near anomalies and are detected with a Gapped Smoothing Method operating on the data and plotting a structural irregularity index as a function of frequency and position.

Abstract: A method for examining quality of a flat panel display device is disclosed, in which good/fail of the flat panel display device is automatically examined to improve efficiency of the operation and obtain exact examined result. The method for examining good/fail of a flat panel display device includes the steps of inputting defect data for each process step, automatically examining good/fail of the panel depending on the input defect data, and measuring good/fail and yield of a glass based on the examined result of the panel.

Abstract: The invention is directed to an ultrasonic testing system. The system tests a manufactured part for various physical attributes, including specific flaws, defects, or composition of materials. The part can be housed in a gantry system that holds the part stable. An energy generator illuminates the part with energy and the part emanates energy from that illumination. Based on the emanations from the part, the system can determined precisely where the part is in free space. The energy illumination device and the receptor have a predetermined relationship in free space. This means the location of the illumination mechanism and the reception mechanism is known. Additionally, the coordinates of the actual testing device also have a predetermined relationship to the illumination device, the reception device, or both.

Abstract: A process management system in accordance with the present invention includes inspection apparatuses for inspecting defects on a wafer, the inspection apparatuses being connected through a communication network, inspection information and image information obtained from these inspection apparatuses being collected to construct a data base and an image file, therein definition of defects is given by combinations of elements which characterize the defect based on the inspection information and the image information obtained from the inspection apparatuses. By giving definition of the defect, characteristics of the defect can be subdivided and known. Therefore, the cause of a defect can be studied.

Abstract: The invention provides a crystal structure analysis method so as to analyze crystal structures in detail. The inventive method comprises incrementing the tilting angle &psgr; of the SBT thin film 1 by one degree in a range of 0 degree ≦y≦90 degrees, for each of the increments of the tilting angle &psgr; irradiating the X-ray onto the SBT thin film with the incident angle &thgr; being incremented by 0.025 degrees in a range of 0 degree ≦&thgr;≦90 degrees and detecting the X-rays diffracted from the SBT thin film 1 by the detector 3.

Abstract: Apparatus for detecting a leak in one or more pockets of one or more blister packs is described. The apparatus comprises means to support the or each pack, means to apply a reduced pressure around the or each pack so as to cause deflection of at least one side of the or each blister pocket, and a scanner means moveable or stationary in relation to the blister pockets, and a computing means. The scanner means is able to scan across at least one side of the or each blister pocket so as to detect the deflection of that side of the or each blister pocket at a reduced pressure, and the computing means compares scans at different pressures over the or each pocket. The apparatus can detect a leak in any format of blister pocket regardless of the shape of the pocket or whether the contents are tablets or capsules. Preferably, the blister packs are supported on a nest or similar means.

Abstract: A segmentation method of a frame of image information including a plurality of spaced DNA spot images corresponding to a plurality of DNA spots. The image information includes image intensity level information corresponding to said DNA spots. A grid including a plurality of spaced grid points corresponding to selected DNA spot images is generated, such that each grid point includes position information indicating the position of the grid point within said frame. For each DNA spot image: (1) background and signal intensity levels are extracted from image characteristic values for the spot image, and (2) difference values between the background intensity levels and signal intensity levels are determined. For each DNA spot: (1) the corresponding difference values are related a range of graphic values, (2) a graphic value for each difference value is selected; and (3) the selected graphic values are displayed.

Abstract: A method for non-destructively inspecting the wall thickness of a component, where the dimensions of the component or of the component surface are measured, substantially without making any contact, and are described by digital data. In accordance with the present invention, a multiplicity of the component's surface points, which substantially completely describe the component, is automatically calculated in a three-dimensional coordinate system. Starting from each of the surface points, going out in one direction that runs perpendicularly to the surface point into the material, one scans for at least one opposite surface point. The wall thickness of the component at the surface point is ascertained as the distance between the surface point and the at least one opposite surface point. The component is visually displayed and, in the visual display, surface points are highlighted for which the wall thickness falls below and/or exceeds one or more predefined values.

Abstract: An absolute position detector that interprets, rather than avoids, abnormal sensory states. Different combinations of sensors in an array are activated as a marker travels along a path. The current activation/deactivation state of the array is converted into a digital signal that is reliably indicative of the current absolute position of the marker along the path. In a preferred embodiment, a dynamic magnetic field is provided whose current condition represents the current absolute position of a moving marker. As the marker moves, the condition of the field changes to activate different groups of Hall Effect devices in an array. The activated groups may comprise one or more Hall Effect devices in the array, depending on the condition of the field as created by the position of the marker. The current activation/deactivation state of the array is then converted, advantageously via truth table logic, into a digital signal representative of the current position of the marker.

Abstract: A method to determine the systematic error of an instrument that measures features of a semiconductor wafer includes the following sequential steps. Collecting sensor data from measurement runs on front and back surfaces of a wafer while the wafer is oriented at different angles to the instrument for each run, yielding a front data set and a back data set for each angle. Then organizing the data in each set into a wafer-fixed coordinate frame. Reflecting all back surface data about a diameter of the wafer creates a reflected back data set. Subtracting the reflected back data from the front data for each wafer angle, and dividing the result by two, yields an averaged wafer shape for each load angle. Adding the reflected back data to the front data and dividing the result by two, yields an instrument signature for each load angle. The symmetric corrector is calculated by taking the average over all instrument signatures at each load angle.

Abstract: A method for monitoring health of a tool includes receiving at least one tool parameter related to the processing of a workpiece in a tool; receiving a model selection trigger; selecting a tool health model based on the model selection trigger; generating at least one predicted tool parameter based on the selected tool health model; and generating a tool health rating for the tool based on a comparison between the measured tool parameter and the predicted tool parameter. A tool health monitor includes a library of tool health models, a model selector, and a fault detection and classification unit. The model selector is adapted to receive a model selection trigger and select a tool health model based on the model selection trigger.

Abstract: A data processing system is provided for use in conjunction with a rail inspection system having a detection carriage with a plurality of sensor units configured to sense discontinuities in a rail of a railroad track as the detector carriage travels along the railroad track. The system includes a data processing and recording computer connectable to the plurality of sensor units for receiving sensor data therefrom. At least one processor card may be included in the data processing and recording computer that includes at least one data object builder configured for building data objects using the sensor data from the plurality of sensor units. The at least one processor card may also include device for synchronizing the data objects with respect to location along the rail. The system may further include a defect detection module in the data processing and recording computer.

Abstract: An abnormality detection apparatus for a position detection device is provided which is capable of performing abnormality detection accurately and inexpensively. The position detection device has a primary winding and a secondary winding, and at least one excitation signal each having a predetermined periodic waveform is supplied to the primary winding to thereby generate at least one output signal each in the form of a phase modulated signal corresponding to a rotational position of a rotating member from the secondary winding directly or after having been subjected to phase shifting and appropriate arithmetic operations. The apparatus is provided with an abnormality detection section for determining an abnormality of the position detection device when the phase modulated signal has a peak value which is outside a predetermined range.

Abstract: A method of determining joint stiffness degradation in structure 10 is provided including a first exciting of the structure 18, a first measuring of transfer function and frequency response function 20, simulating a mileage accumulation process of the structure 16 performed after the first exciting 18 and the first measuring 20, a second exciting of the structure 22, performed after the simulating a mileage accumulation process 16, a second measuring of frequency response function 24 performed after the simulating a mileage accumulation process 16 and calculating the change in joint stiffness 26 using the first measuring 20 and the second measuring 24.

Abstract: Apparatus for detecting a leak in one or more pockets of one or more blister packs is described. The apparatus comprises means to support the or each pack, means to apply a reduced pressure around the or each pack so as to cause deflection of at least one side of the or each blister pocket, and a scanner means moveable or stationary in relation to the blister pockets, and a computing means. The scanner means is able to scan across at least one side of the or each blister pocket so as to detect the deflection of that side of the or each blister pocket at a reduced pressure, and the computing means compares scans at different pressures over the or each pocket.

Abstract: A pipeline surveying system including a pipeline pig can accurately provide a pipeline profile after correlation with a previously determine Global Positioning System (GPS) survey. An inertial measurement unit located in the pig determines a pipeline profile as it travels through the pipeline and correlates the measured profile with the GPS survey.

Abstract: A process management system in accordance with the present invention includes inspection apparatuses for inspecting defects on a wafer, the inspection apparatuses being connected through a communication network, inspection information and image information obtained from these inspection apparatuses being collected to construct a data base and an image file, therein definition of defects is given by combinations of elements which characterize the defect based on the inspection information and the image information obtained from the inspection apparatuses. By giving definition of the defect, characteristics of the defect can be subdivided and known. Therefore, the cause of a defect can be studied.

Abstract: An apparatus is described for detecting the early signs of cycle-induced fatigue and thereby predicting failure of the rotating disk in turbo-machinery. It identifies change in shape of the entire disk in radial, tangential and axial directions. It examines these deformations as a function of rotational velocity and compares them to a data base of deformations due to cracks in the rotor. Blade-tip measurements are processed through specialized algorithms to detect such asymmetry during operation, providing a real-time, non-destructive method of prediction. The sensors can be housed within the machinery case, and are capable of operating in harsh environments while maintaining adequate stand-off distance, making the entire apparatus robust enough for conditions in high-speed turbo-machinery.

Abstract: A modular materials characterization apparatus includes a sensor array disposed on a substrate, with a standardized array and contact pad format; electronic test and measurement apparatus for sending electrical signals to and receiving electrical signals from the sensor array; an apparatus for making electrical contact to the sensors in the standardized array format; an apparatus for routing signals between one or more selected sensors and the electronic test and measurement apparatus and a computer including a computer readable having a computer program recorded therein for controlling the operator of the apparatus. The sensor array is preferably arranged in a standardized format used in combinatorial chemistry applications for rapid deposition of sample materials on the sensor array.

Abstract: A motor vehicle is provided with a weight control system utilizing the on-board weighing of the driver and one or more passengers. The display and input are effected through a touch screen and/or voice commands and the individuals's identification is registered in memory as are previous weighing states so that with control progress can be monitored. To compensate for different clothing and footwear which might contribute to false reading, the system dialogues with the individual with respect to clothing and footwear.

Abstract: A power steering apparatus includes a motor, a torque sensor, and a motor resolver. The motor generates an assisting force to reduce the steering force of the steering wheel. The torque sensor detects the steering torque of the steering wheel. The motor resolver detects the rotational angle of the motor. An electronic control unit (ECU) detects the absolute position of the steering wheel based on a detection signal Rt sent from a second resolver of the torque sensor and a detection signal Rm sent from a motor resolver. As a result, the cost is reduced and the absolute position of the steering wheel is accurately detected.

Abstract: An inspecting apparatus and method for inspecting cell badness in a liquid crystal display device that is adaptive for shortening an inspection time and improving a work efficiency in a bad pixel inspecting work as well as improving a yield in a repairing work. In the apparatus, a pointing device freely moves a cursor emerging on the screen of the liquid crystal display panel in all the direction to acquire co-ordinate values of bad pixels. A file server stores the co-ordinate value of the bad pixels acquired by the pointing device. Accordingly, an co-ordinate value acquisition work of the bad pixels emerging on the liquid crystal display panel can be rapidly made to shorten an inspection time, and the acquired co-ordinate value can be automatically stored and automatically transmitted to a repairing device to improve a yield in the repair work.

Abstract: A method and system for evaluating structural defects in metals is provided. In one embodiment, the method recognizes that the acceptability of a given defect is principally determined by the four basic parameters of operating temperature, operating stress, defect area, and defect shape. Ranges are established for each of these four basic parameters, and intermediate values within these ranges are selected to create a series of index value data sets. The method evaluates these index value data sets by calculating a life cycles estimate for each. Using statistical methods, the life cycles results are analyzed to determine the effect each of the four basic parameters has on the life of a component with a defect. Understanding the relationship between these four basic parameters and life cycles enables the method to provide an interpolation algorithm for finding the life cycles for any component having a defect.

Abstract: A panel tester and grader includes a main frame including a plurality of rollers and defining a substantially S-shaped testing path. A substantially linear bypass path extends below the testing path and a bypass assembly is coupled to the main frame and is operable to move the main frame between a testing position in which panels are received by the testing path, and a bypass position in which panels are received by the bypass path. A load cell providing a load output is coupled to a deflector roller to measure a load applied to the panel by the deflector roller. The load output is monitored as the panels are guided through the panel tester and the load output is selectively recorded based upon the monitored load output.

Abstract: A foreign material interference detection apparatus for an opening/closing member that reduces the calculation load for foreign material interference determination processing. A rotating speed detection sensor detects the rotating speed of a motor and provides its detection signal SP to a computer. The computer obtains a load determination rotating cycle t1 from the detection signal SP. Based on the load determination rotating cycle t1, the computer determines foreign material interference when it determines that the rotating speed is fluctuating due to a load that is the same as that produced when a foreign material is interfering with the opening/closing member and when the determination is made consecutively a predetermined number of times.

Abstract: A shape estimating method by which, also where a chemically amplified resist is used, the shape of the resist can be estimated accurately by a computer simulation. Diffusion of a catalyst species in a chemically amplified resist upon the post-baking process is calculated by approximation with a Gaussian distribution, and a light intensity distribution on the chemically amplified resist upon exposure to light is calculated. Then, the light intensity distribution is corrected with the calculated Gaussian distribution, and calculation of the shape of a two-dimensional pattern of the chemically amplified resist is performed based on the corrected light intensity distribution. Preferably, as the Gaussian distribution, a Gaussian distribution which approximates isotropic distribution of a catalyst species with a diffusion length used as a parameter is used.

Abstract: A panel tester and grader includes a main frame including a plurality of rollers and defining a substantially S-shaped testing path. A substantially linear bypass path extends below the testing path and a bypass assembly is coupled to the main frame and is operable to move the main frame between a testing position in which panels are received by the testing path, and a bypass position in which panels are received by the bypass path. A load cell providing a load output is coupled to a deflector roller to measure a load applied to the panel by the deflector roller. The load output is monitored as the panels are guided through the panel tester and the load output is selectively recorded based upon the monitored load output.

Abstract: A signal analysis system and method for analyzing an input signal acquired from a mechanical system. The mechanical system may include at least one rotating apparatus. The signal analysis system may be configured to: (a) receive samples of the input signal, (b) perform an invertible joint time-frequency transform (e.g.

Abstract: A system adds functionality to a power button where use of the power button controls the entry and exit from a diagnostic mode. The system includes an information appliance connected to a diagnostic appliance. Once an information appliance is powered up, the information appliance monitors its power button for a press which indicates a request to enter a diagnostic mode. Absent a press of the power button, the system continues to be under control of the information appliance and never enters a diagnostic mode. However, if a press of the power button is detected, the system enters a diagnostic mode. Once in a diagnostic mode the system provides an exit therefrom by interpreting a power button press as a request to exit. The window of time to make such an exit closes once the diagnostic appliance achieves communication with the information appliance. If the power button is pressed during this window of time, then the system ends its diagnostic mode and control of the system returns to the information appliance.

Abstract: An abnormality detection apparatus for a position detection device is provided which is capable of performing abnormality detection accurately and inexpensively. The position detection device has a primary winding and a secondary winding, and at least one excitation signal each having a predetermined periodic waveform is supplied to the primary winding to thereby generate at least one output signal each in the form of a phase modulated signal corresponding to a rotational position of a rotating member from the secondary winding directly or after having been subjected to phase shifting and appropriate arithmetic operations. The apparatus is provided with an abnormality detection section for determining an abnormality of the position detection device when the phase modulated signal has a peak value which is outside a predetermined range.

Abstract: A diagnostic technique for monitoring shaft cracking or incipient pinion slip involves monitoring a shift in a characteristic natural frequency of an operating system such as a geared system of a locomotive. The technique involves monitoring a shift in the characteristic natural frequency or resonance of a shaft for detecting shaft cracking. The technique also involves monitoring a shift in the characteristic natural frequency of one or more assemblies of the operating system which include a pinion and detecting a shift in the one or more characteristic natural frequencies of the assemblies. A vibration sensor or measurement of current changes of a motor of the operating system can be used to detect vibrations to monitor the characteristic natural frequencies. Torsional oscillations or measurement of current and voltage changes of a motor of the operating system, can also be used to monitor the characteristic natural frequencies.

Abstract: A data processing system is provided for use in conjunction with a rail inspection system having a detection carriage with a plurality of sensor units configured to sense discontinuities in a rail of a railroad track as the detector carriage travels along the railroad track. The system comprises a data processing and recording computer connectable to the plurality of sensor units for receiving sensor data therefrom. At least one processor card may be included in the data processing and recording computer that includes at least one data object builder configured for building data objects using the sensor data from the plurality of sensor units. The at least one processor card may also include means for synchronizing the data objects with respect to location along the rail. The system may further comprise a defect detection module in the data processing and recording computer.

Abstract: A method and apparatus for dynamically measuring a railroad track condition using a railroad truck with metal track engaging wheels as a reference platform from which a line of sight reference plane spaced from the track is created. Measurements are successively taken between the track and the reference plane as the railroad truck moves along the track.

Abstract: In incremental detectors, measurement signals thereof are first corrected in graduation-specific fashion with respect to amplitude offsets, and phase displacement, and a rough angle is determined. The residual error of the rough angle is fine-corrected via rough-angle-specific, graduation-independent rough angle correction values and a position signal is determined in this way. The correction values for amplitudes offsets, and phase displacement are determined using regression, and the rough angle correction values are determined using high-precision reference angle measurements.

Abstract: There is provided an improved panel tester and grader which is used for determining the strength and stiffness values for individually tested panels. In one aspect of the present invention, an improvement resides in providing an apparatus and method which more accurately determines when a panel is properly located within a test load zone such that certain measurements regarding the panels characteristics may be properly measured. These variables ultimately contribute to the calculated overall strength and stiffness values. Pairs of opposing rolls are provided to process the panels therebetween along a processing line. The opposing rolls each include a groove extending completely around their outer surfaces. The grooves of the opposing rolls are aligned so as to define respective channels extending between the pairs of opposing rolls. Individual location sensors are positioned relative to the channels to determine where the panels are located along the processing line at any given moment.

Abstract: The present invention relates to a method for monitoring the creep behavior of rotating components of a compressor stage or turbine stage. In the method, at least one test element (2) is mounted in a region of the compressor stage or turbine stage in which said test element is exposed to an operating load comparable to that of the component to be monitored. The test element (2) is investigated after a predeterminable operating period of the component to be monitored. Finally, the creep behavior of the component to be monitored is derived from the creep behavior of the test element.

Abstract: Controlling processes comprising detecting and measuring a parameter, for example presence and location of an element of a good, with at least two determinations as representations of the target parameter, transmitting signals to the computer, and processing the signals to compare the parameter to acceptable conditions. The detection can include three or more replications, optionally each for at least two parameters, optionally using at least two different methods to analyze the signals. The invention contemplates detecting and analyzing the target parameters using two or more analytical tools within the respective image to detect a given component of the product, namely two or more measurements of the parameter on a single visual image.