Two-dimensional code reader

• US 6,081,627 A
• Filed: 08/22/1997
• Issued: 06/27/2000
• Est. Priority Date: 08/23/1996
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Kojima, Yoshihiro, Kobayashi, Keiichi, Inoue, Katsushi, Kannon, Tetsuya
• Primary Examiner(s): Couso, Jose L.
• Assistant Examiner(s): Do, Anh Hong
• Application Number:
  US08/917,051
• Time in Patent Office: 1,040 Days
• Field of Search: 382/312, 382/313, 382/318, 382/321, 235/494, 235/455
• US Class Current: 382/312
• CPC Class Codes: G06K 7/1093 sensing, after transfer of the image of the data-field to an intermediate store, e.g. storage with cathode ray tube
• CPC Class Codes: G06K 7/14 using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence
• CPC Class Codes: G06K 7/1478 adapting the threshold for pixels in a CMOS or CCD pixel sensor for black and white recognition

Abstract

A two-dimensional code reader for precisely and fast reading a two-dimensional code image containing luminance unevenness caused by variations in illumination, etc. To binarize cells, first the gray levels of the pixels at the center points of the cells are extracted, a local threshold value is found only from the extracted gray levels, and the gray levels are compared with the local threshold value, thereby binarizing the cells.

Claims

1. A two-dimensional code reader comprising:

conversion means for receiving light reflected from two-dimensional code and converting the light into an image signal;

storage means for storing the image signal as an image memory;

code detection means for providing from the image memory a detected two-dimensional code; and

cell binarization means for binarizing values of predetermined pixels for respective cells on the detected two-dimensional code, said cell binarization means comprising;

cell gray level extraction means for finding respective gray levels of the predetermined pixels based on image signals obtained from the predetermined pixels of the cells on the detected two-dimensional code;

local threshold value determination means for finding a local threshold value from the gray levels determined by said cell gray level extraction means; and

cell binary determination means for comparing each of the gray levels found by said cell gray level extraction means with the threshold value found by said local threshold value determination means to find binary data for a corresponding cell;

wherein said local threshold value determination means defines a plurality of small areas, finds an average value and amplitude of maximum and minimum values of the gray levels of the predetermined pixels of the cells located in each of the small areas, compares adjacent small areas in terms of amplitude, and if one of the small areas has an amplitude of a predetermined value or less as compared with the other, determines a threshold value of the former small area based on the latter small area.

2. The two-dimensional code reader as claimed in claim 1 wherein said local threshold value determination means compares the adjacent small areas in terms of amplitude, and unless one of the small areas has the amplitude of the predetermined value or less as compared with the other, adopts an average value of the average values found in the small areas as a threshold value of the former small area.