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Electrically Thresholding an Optical Signal

IP.com Disclosure Number: IPCOM000060589D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Linger, C: AUTHOR

Abstract

Any digital processing of an image goes through a step of data entry, and processing quality often depends on the quality of the digital information entered. It is necessary to check the source power to cause the sensor to operate over all the response range thereof and also the threshold in accordance with the time required to rise from black to white. The true value of the thresholded signal is at 50% of the corresponding value from black to white with an increment of uncertainty (positive or negative) due to the digitizing step. A problem is raised by the fact that light energy is not constant over all the sensor range and that the amplitude varies when the sensor traverses the object to be examined. In the case of a metallized ceramic substrate (Fig. (1.B)), the image is schematically shown by envelope A of Fig. 1(A).

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Electrically Thresholding an Optical Signal

Any digital processing of an image goes through a step of data entry, and processing quality often depends on the quality of the digital information entered. It is necessary to check the source power to cause the sensor to operate over all the response range thereof and also the threshold in accordance with the time required to rise from black to white. The true value of the thresholded signal is at 50% of the corresponding value from black to white with an increment of uncertainty (positive or negative) due to the digitizing step. A problem is raised by the fact that light energy is not constant over all the sensor range and that the amplitude varies when the sensor traverses the object to be examined. In the case of a metallized ceramic substrate (Fig. (1.B)), the image is schematically shown by envelope A of Fig. 1(A). The threshold at 50% of the image of the object to be examined will be the threshold at 50% of the envelope A. (Refer to the curve indicated "Threshold 50%".) To this end, information from the sensor is digitized by an analog-to-digital converter (ADC), then stored in a buffer A, then transferred into the computer which processes signal B (Fig. 1(A). The processing step allows the envelope of the source from this value to be calculated. It is easy to calculate the value of the theoretical threshold at 50%, the digitizing uncertainty being calculated in accordance with the rise times a and b (Fig. 2). However, it is to be noted that the rise time is constant with the same optics. Thresholding quality increases with the rise time of the signal transition from black to white. To make sure that the defect image is valid, it would be necessary to add a positive correction (+) to the positive threshold (+) and, conversely, a negative correction (-) to the negative threshold (-). Thus, for processing an image, it would be necessary to operate with two thresholds. The value of these thr...