Method of reading bar code

(54) METHOD OF READING BAR CODE

FOREIGN PATENT DOCUMENTS

(75) Inventors: Hisashi Shigekusa, Okazaki; Masami Tanaka, Handa; Tadao Oshima,

Nagoya, all of (JP)

(73) Assignee: Denso Corporation, Kariya (JP)

( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 0 days.

(21) Appl. No.: 09/438,847

(22) Filed: Nov. 12, 1999

(30) Foreign Application Priority Data

Nov. 16, 1998 (JP) 10-325278

Sep. 24, 1999 (JP) 11-270926

(51) Int. CI. G06K 5/04

(52) U.S. CI 235/462.12; 235/462.09;

235/462.16

(58) Field of Search 235/462.01, 462.08,

235/462.09, 462.11, 462.12, 462.15, 462.41, 462.16, 462.19

(56) References Cited

U.S. PATENT DOCUMENTS

4,717,818 * 1/1988 Broockman et al 235/462.12

5,128,527 * 7/1992 Kawai et al 235/462.12

5,241,164 * 8/1993 Pavlidis et al 235/462.12

5,304,787 * 4/1994 Wang 235/470

5,457,308 * 10/1995 Spitz et al 235/462.12

5,550,365 * 8/1996 Klancnik et al 235/462.12

5,739,518 * 4/1998 Wang 235/454

5,764,798 6/1998 Liu 382/190

5,854,479 * 12/1998 Watanabe et al 235/462.12

5,917,172 * 6/1999 Watanabe et al 235/462.12

5,942,740 * 8/1999 Watanabe et al 235/462.07

A method of reading a bar code having guard bars at both sides thereof without fail even if the bar code image is highly distorted. An image region taken in by a CCD camera is scanned in horizontal and/or vertical directions to find out a first guard bar in the bar code. Then, a first scanning line for reading the bar code is set in a direction perpendicular to the first guard bar. The bar code is scanned along the first scanning line. If the first scanning line goes out of the bar code region, the first scanning line is traced back to a bar which is last read. Another scanning line starting from the last read bar and extending perpendicularly thereto is set to read the rest of the bar code. This process is repeated until the second guard bar is detected and a whole bar code is completely read. The first scanning line may be set, so that it only reads a predetermined number of bars and the rest of the bar code is read by new scanning lines starting from the last read bar. Alternatively, the bar code region is searched by preliminarily scanning the image region divided into plural rectangular sections. The bar code region is determined based on the number of brightness changes in each divided section. The first guard bar in the bar code can be easily found in this manner.

21 Claims, 22 Drawing Sheets