Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1998-08-11
2001-04-17
Mancuso, Joseph (Department: 2623)
Image analysis
Applications
Manufacturing or product inspection
C345S904000, C348S092000, C324S701000
Reexamination Certificate
active
06219443
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and apparatus for testing displays and, more particularly, to a method and apparatus for testing displays that utilizes a CCD camera having a relatively low resolution compared to the resolution of a display being inspected.
BACKGROUND OF THE INVENTION
Currently, most if not all cathode ray tubes (CRT) and liquid crystal displays (LCDs) are inspected visually to determine if all of the pixels in the display are functioning correctly. This is accomplished by displaying one or more patterns on the display while a person observes the pattern to spot defects. This method has several disadvantages. One disadvantage is that the person observing the patterns on the display must look closely and carefully at the entire screen in order to spot defects, which can be very time consuming, thus adding to the costs associated with the inspection. Another disadvantage of this method is that human beings are not always highly consistent in this type of inspection and, therefore, results can vary from day-to-day when performed by the same person and from person to person when performed by different people.
It is also known to inspect displays using high-resolution cameras. However, this type of inspection requires that the camera used to inspect the display have a higher resolution than the display being inspected. If the display has a low resolution, it is possible to use a high-resolution camera to inspect the display by feeding the output of the camera into a computer and having the computer analyze patterns on the display to determine whether or not defects exist in the display.
In most cases, a nine-to-one increase in the number of camera pixels to the number of display pixels is required in order to properly inspect the displays. This ratio requirement effectively limits the resolution of the display that can be tested and/or adds greatly to the cost of the camera used for the inspection. Furthermore, if a single camera is used to perform the inspection and the camera resolution is close to the display resolution, then the detection system can only detect large defects, i.e., defects covering more than a four-pixel area. Multiple cameras can be used in place of a single high-resolution camera to perform the inspection. However, using multiple cameras can greatly increase inspection time and cost of the test due to the added costs due to the added costs of multiple cameras and additional processing time.
Accordingly, a need exists for a method and apparatus for inspecting displays for defects which is capable of efficiently detecting defects, including small defects, and which overcomes the disadvantages of the existing inspection systems and methods.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for detecting defects in a display. The apparatus of the present invention comprises a camera for capturing an image of a display being inspected and processing circuitry, such as, for example, a microprocessor or a digital signal processor (DSP), for processing the captured image to determine whether or not the display being inspected is defective. Preferably, the processing circuitry is a microprocessor running image processing software which controls data acquisition as well as the processing of the acquired data to determine whether the display being inspected is defective. In accordance with the present invention, a relatively high resolution display can be inspected using a single camera, preferably a charge-coupled device (CCD) camera, which has a lower resolution than the display being inspected.
The camera is focused on the display such that the entire display is within the field of view of the camera. The camera then captures an image of the display, digitizes the image and stores the digitized image in a memory device which is in communication with the processing circuitry. The processing circuitry then reads the image data out of memory and averages all of the image data to obtain an average value corresponding to the brightness of the display. In accordance with a first embodiment of the present invention, once this average value has been obtained, blocks of the image data are read out of memory, such as, for example, 4×4 pixel blocks, and each of the blocks are averaged and compared to the display average to determine whether or not the average value for each of the blocks is equal to the average value for the entire display. The result of this comparison is then stored in memory. The next block of data is then read out of memory, averaged, and the block average is compared to the display average.
This process is performed until the last block of the image data has been processed. The processing circuitry then analyzes the results to determine the locations of defects in the display and the results of the inspection are then stored in memory and/or output to a peripheral device coupled to the processing circuitry such as, for example, a display monitor, so that the person performing the inspection is informed of the locations of any defects in the display being inspected. If a defect is found in any block of image data, the location of the defect is known by the processing circuitry because the manner in which the pixel coordinates on the display are mapped into locations in memory is known by the processing circuitry, as will be understood by those skilled in the art. Therefore, once a defect is found in a block of image data, the location of the pixels on the display that correspond to the block of image data can be determined by the processing circuitry.
In accordance with a second embodiment of the present invention, the processing circuitry averages the image data corresponding to the entire display and then calculates the standard deviation for the entire display. This standard deviation is then compared to an acceptable standard deviation for the particular type of display being inspected and the results of the comparison are stored in memory and/or are output on a peripheral device coupled to the processing circuitry such as, for example, a display monitor, so that the person performing the inspection is informed of the results of the inspection. By using the standard deviation process, large areas of weak pixels and cloudy areas in the display being inspected can be located.
In accordance with a third embodiment of the present invention, large blocks of the image data are read out of memory and each block, which may be, for example, a 100×100 block of pixels, is averaged and the average of each block is compared to the display average by using the process discussed above with respect to the first embodiment. However, after each block has been averaged and compared to the display average, a standard deviation value is calculated for each block and a determination is made as to whether the standard deviation for each block is acceptable. The results of this determination are stored in memory and/or output via a peripheral device to the person performing the inspection.
In accordance with the preferred embodiment of the present invention, the present invention utilizes a process which incorporates the processes of the first, second and third embodiments of the present invention. In accordance with the preferred embodiment, once the average and standard deviation have been computed for the entire display image, a determination is made as to whether the standard deviation and the average for the display image is within the specification limits for the particular display being inspected. If not, the process and circuitry of the present invention determines that the display has failed the inspection test. If the computed average and standard deviation are within specification limits, each pixel on the display is compared with the display average +/− an offset, which is a predetermined tolerance value that depends on the type of display being inspected and on the application for which the display will be used. The results of this comparison are then us
Agilent Technologie,s Inc.
Bali Vikkram
Mancuso Joseph
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