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Distinguishing Printing on Dark Backgrounds

IP.com Disclosure Number: IPCOM000074316D
Original Publication Date: 1971-Apr-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Wilson, MG: AUTHOR

Abstract

In conventional optical character recognition machines, a video signal from photodetector 11 is amplified by amplifier 12, whose output 13 is transmitted to one input of discriminator 14. Amplifier output 13 is also coupled to white follower 15, whose output 16 is coupled to the other input of discriminator 14. Discriminator 14 thresholds the signal on output 13 against a function of the signal on output 16 to produce on line 17, a digitized signal having a low-fixed voltage corresponding to the "white" background 21 of document 20, and a higher fixed voltage corresponding to printing 22 on document 20.

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Distinguishing Printing on Dark Backgrounds

In conventional optical character recognition machines, a video signal from photodetector 11 is amplified by amplifier 12, whose output 13 is transmitted to one input of discriminator 14. Amplifier output 13 is also coupled to white follower 15, whose output 16 is coupled to the other input of discriminator 14. Discriminator 14 thresholds the signal on output 13 against a function of the signal on output 16 to produce on line 17, a digitized signal having a low-fixed voltage corresponding to the "white" background 21 of document 20, and a higher fixed voltage corresponding to printing 22 on document 20.

Conventional white followers 15 have a time constant much higher than that of the video system 10 as a whole, in order to filter out noise variations in the background 21. In some applications, however, printing 22 may occur near the edge of a background area 23 which is substantially darker than background area 21. Area 23 may represent, for instance, a mailing label on an envelope. Curve 31 on graph 30 shows the difference voltage between outputs 13 and 16 for a conventional white follower 15 along a scanning path, such as 24. When path 24 intersects boundary 25 of area 23, curve 31 ascends sharply at 32 past threshold level 33. Curve 31 then descends slowly until the color of area 23 is again recognized as "white" at point 34. But, since the first two black peaks of the letter "M" of printing 22 occur before point 34,...