Multiple threshold encoding of machine readable code

• US 5,278,400 A
• Filed: 08/19/1991
• Issued: 01/11/1994
• Est. Priority Date: 08/19/1991
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Appel, James J.
• Primary Examiner(s): Hajec, Donald
• Assistant Examiner(s): Chin, Esther
• Application Number:
  US07/742,965
• Time in Patent Office: 876 Days
• Field of Search: 235/494, 235/454, 235/456, 235/460, 235/465, 358/429, 358/455
• US Class Current: 358/3.28
• CPC Class Codes: G06K 19/06037 multi-dimensional coding
• CPC Class Codes: G06K 7/14 using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence

Abstract

A method and apparatus for applying coded data to a substrate and decoding the data in which the data are encoded in cells having a determined number of pixels. The pixels are coded, preferably by binary printing, in accordance with the number of coded pixels and not their position. In decoding of the cells, the gray scale levels of the pixels are sensed, and converted to digital signals. The digital signals are summed, for all of the pixels of the cell, and compared with multiple threshold levels in order to recover the data.

Claims

1. A method for decoding a cell of an image having a plurality of pixels, comprising:

(a) detecting the gray scale level at each pixel of the cell an converting each of the detected gray scale levels to a digital signal representing the detected gray scale level of the respective pixel,

(b) dividing the maximum output range of said detected gray scale levels into a plurality of contiguous signal level ranges,

(c) summing the values of the detected digital signals corresponding to the gray scales of the pixels of the cell, and comparing said sum with a plurality of threshold levels to determine the level range within which the sum S falls, whereby the determined signal range represents the coding of the cell, and outputting a signal corresponding to said range.

2. A method for decoding a cell of an image having N pixels, comprising:

detecting the gray scale level of each pixel of the cell and converting each of the detected gray scale levels to a L bit digital signal representing the gray scale level of the respective pixel, wherein N and L are integers;

whereby the digital signal corresponding to each pixel may have a maximum of 2^L different values;

summing the digital signals representing all of the pixels of the cell, whereby the resultant sum S may have maximum value of N×

(2^L -1);

defining N different threshold levels separating said maximum value into N+1 level ranges;

comparing said sum S with the threshold levels to determine the level range within which said sum falls; and

outputting said determined level range, whereby said determined level range corresponds to the coding of pixels of said cell.

3. A method for coding information on a substrate, comprising

defining an image cell of a predetermined number N of pixels on said substrate,

selectively correlating information to be encoded to different numbers M from 0 to N, and

distinctively marking M of said pixels on said substrate, with respect to the remaining pixels thereof, irrespective of the relative location of the marked pixels in the cell.

4. The method of claim 3 wherein said step of marking comprises binary printing said pixels on said substrate.

5. A method for encoding data on and recovering it from a substrate, comprising marking pixels of a cell on said substrate with binary printing;

sensing the gray levels of said pixels and converting the sensed levels to digital signals;

summing said digital signals, and comparing the sum thereof with a plurality of different threshold levels, to determine a range of levels within which said sum falls; and

outputting a signal corresponding to said determined range.

6. An apparatus for decoding a cell of an image having a plurality of pixels, comprising:

means for detecting the gray scale level at each pixel of the cell;

means for converting each of the detected gray scale levels to a digital signal representing the detected gray scale level of the respective pixel,

means for defining a plurality of threshold levels;

means for summing the values of the detected digital signals corresponding to the gray scales of the pixels of the cell;

means for comparing said sum with said threshold levels to determine a level range within which said sum falls, whereby the determined signal range represents the coding of the cell, and

means for outputting a signal corresponding to said determined range.

7. An apparatus for coding information on a substrate, comprising

means for defining an image cell of a predetermined number N of pixels on said substrate,

means for selectively correlating information to be encoded to different numbers M from 0 to N, and

means for distinctively marking M of said pixels on said substrate, with respect to the remaining pixels thereof, irrespective of the relative location of the marked pixels in the cell.

8. The apparatus of claim 7 wherein said means for marking comprises means for binary printing said pixels on said substrate.