Browse Prior Art Database

Video Thresholding for Photodetector Arrays

IP.com Disclosure Number: IPCOM000080045D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Siverling, MM: AUTHOR

Abstract

High-resolution multichannel photodetector arrays may be employed in reading characters or other data from documents. To set a threshold level for the video signals from such arrays, it is desirable to determine a level related to the average blackness of the character seen by the array. In the multichannel thresholder shown in Fig. 3, U. S. Patent 3,701,099 issued to R. E. Hall et al., a set of diodes m0-mn derives a signal Vj directly proportional to the largest signal from the channels. That circuit, however, allows the thresholder to be swamped by very small but very black extraneous marks, so that a lighter character is buried.

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Video Thresholding for Photodetector Arrays

High-resolution multichannel photodetector arrays may be employed in reading characters or other data from documents. To set a threshold level for the video signals from such arrays, it is desirable to determine a level related to the average blackness of the character seen by the array. In the multichannel thresholder shown in Fig. 3, U. S. Patent 3,701,099 issued to R. E. Hall et al., a set of diodes m0-mn derives a signal Vj directly proportional to the largest signal from the channels. That circuit, however, allows the thresholder to be swamped by very small but very black extraneous marks, so that a lighter character is buried. On the other hand, the averaging of video signals from the channels would be sensitive to overall character height: a short character would produce a much smaller average than a tall character of equal contrast.

Circuit 10 overcomes these difficulties by providing a weighted black peak signal for a video thresholder. Multichannel integrated photodetector array 11 produces analog video signals on lines 12. These lines are coupled to the respective inputs of STAGE phi - STAGE n of Patent 3,701,099. Some of the signals, from every fifth channel for instance, are coupled through diode-resistor circuits to line 13.

The weighted black peak signal on line 13 may be connected to point 58 of the aforementioned patent, replacing the diodes m0-mn. A channel line 12-1, for example, having a signal level lower than that at line 13, does not contribute to the weighted-peak signal...