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Browse Prior Art Database

Switching of Threshold Value for Document Scan

IP.com Disclosure Number: IPCOM000043582D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Sugita, S: AUTHOR [+2]

Abstract

Preceding document scan, a CCD (charge-coupled device) sensor unit views a white-colored reference zone. A control unit responds to the output signal of the CCD sensor unit for generating a set of threshold values, one of which is selectively fetched and supplied to a comparator which compares the threshold value and the output signal of the CCD sensor unit for successive pel (picture element) positions on the document. In Fig. 1, the white-colored reference zone 1 is provided on table 2 on which the document 3 is placed. The optical system, including light source 4, lens 5 and the CCD sensor unit 6, and the table are moved relative to each other to sequentially scan the white-colored reference zone 1 and the document 3. Initially, the white-colored reference zone 1 is scanned. Referring to Fig.

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Switching of Threshold Value for Document Scan

Preceding document scan, a CCD (charge-coupled device) sensor unit views a white-colored reference zone. A control unit responds to the output signal of the CCD sensor unit for generating a set of threshold values, one of which is selectively fetched and supplied to a comparator which compares the threshold value and the output signal of the CCD sensor unit for successive pel (picture element) positions on the document. In Fig. 1, the white-colored reference zone 1 is provided on table 2 on which the document 3 is placed. The optical system, including light source 4, lens 5 and the CCD sensor unit 6, and the table are moved relative to each other to sequentially scan the white-colored reference zone 1 and the document 3. Initially, the white-colored reference zone 1 is scanned. Referring to Fig. 2, the output signal of the CCD sensor unit 6 is applied to input terminal 7. The output signal is supplied to analog-to-digital (A/D) converter 9 through amplifier 8. At this initial scan of the white-colored reference zone 1, the digital signal from the A/D converter 9 is supplied to control unit 12 through latch 10 and data bus 11. The control unit 12 generates a set of threshold values, such as Threshold #1, #2, #3, #4 and #5 (Fig. 3) in response to the digital signal which represents the reflected light from the white-colored reference zone 1. The generated threshold values are stored in table 14 of memory 15 through data bus 13. Fig. 4 shows frequency distribution curves which represent the number of pels in one pel line for parameter of light intensity. Curve A represents the frequency distribution of the white-colored reference zone 1. Curve B represents the frequency distribution in one pel line inclu...