Recognizing dataforms in image areas

• US 5,867,594 A
• Filed: 11/01/1996
• Issued: 02/02/1999
• Est. Priority Date: 06/15/1994
• Status: Expired due to Fees

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Metanetics Corporation
• Inventors: Cymbalski, Robert Stanley
• Primary Examiner(s): Couso, Jose L.
• Application Number:
  US08/742,368
• Time in Patent Office: 823 Days
• Field of Search: 382/168, 382/169, 382/170, 382/171, 382/173, 382/174, 382/177, 382/181, 382/182, 382/183, 382/190, 382/192, 235/462, 235/463, 235/464, 235/465, 235/494
• US Class Current: 382/192
• CPC Class Codes: G06V 10/255 Detecting or recognising potential candidate objects based on visual cues, e.g. shapes
• CPC Class Codes: G06V 30/2247 Characters composed of bars, e.g. CMC-7
• CPC Class Codes: G06V 30/413 Classification of content, e.g. text, photographs or tables

Abstract

Dataforms, such as bar codes and matrix codes, are recognized by analysis of histogram type data derived for a plurality of window sections of an image area. Typically, an image area 512 pixels high by 480 pixels wide is divided into 240 window areas, each including 1024 pixels in a 32 by 32 pixel square. A histogram for a window section overlying a portion of the dataform may typically exhibit two peaks representing the two principal reflective values (black and white, for example) of the elements and spaces of a dataform. A background (quiet zone) window section histogram exhibits one principal peak representing the background value (white, for example). The background window sections and the dataform window sections are assigned to two different groups. One or both groups are then used for one or more of the following: recognizing the presence of a dataform; determining whether the dataform is darker or lighter than the background; and locating the dataform within the image area. Also, a single histogram is used to identify the type of dataform, based upon the histogram signature of the dataform.

Claims

1. A method for evaluating an image and identifying characteristics of a dataform therein, the method comprising the steps of:

(a) sampling a portion of an image comprised of a plurality of pixels, to obtain a plurality of reflective values respectively associated with the plurality of pixels;

(b) determining, for each said portion of the image, the number of occurrences of each reflective value of said plurality of reflective values, wherein the number of occurrences are occurrence data;

(c) categorizing the occurrence data in one of the following groups;

(i) first occurrence data indicative of presence of a first principal reflective value and a second principal reflective value, wherein said first and second principal reflective values have a relatively greater number of occurrences in said portion of the image than other reflective values therein, and

(ii) second occurrence data indicative of presence of a third principal reflective value, wherein said third principal reflective value has a relatively greater number of occurrences in said portion of the image than other reflective values therein;

(d) repeating steps (a), (b) and (c) for one or more portions of the image to provide at least one first occurrence data and at least one second occurrence data;

(e) comparing each of the first and second principal reflective values to the third principal reflective value; and

(f) determining which of the first and second principal reflective values is most distinct from the third principal reflective value.

2. A method according to claim 1, wherein said step of determining the number of occurrences of each reflective value of said plurality of reflective values includes the step of deriving histogram data.

3. A method according to claim 1, wherein each of said plurality of reflective values is indicative of a respective color.

4. A method according to claim 1, wherein said first principal reflective value is indicative of the presence of a first color, said second principal reflective value is indicative of the presence of a second color, and said third principal reflective value is indicative of the presence of a third color.

5. A method according to claim 4, wherein the presence of said first and second colors is indicative of a dataform, and the presence of said third color is indicative of a background area.

6. A method according to claim 5, wherein said first principal reflective value corresponds to a relatively dark color and said second principal reflective value corresponds to a relatively light color.

7. A method according to claim 6, wherein said method further comprises:

determining that the dataform is darker than the background area if said first principal reflective value is most distinct from the third principal reflective value; and

determining that the dataform is lighter than the background area if said second principal reflective value is most distinct from the third principal reflective value.

8. A method according to claim 5, wherein said first principal reflective value corresponds to a relatively light color and said second principal reflective value corresponds to a relatively dark color.

9. A method according to claim 8, wherein said method further comprises:

determining that the dataform is lighter than the background area if said first principal reflective value is most distinct from the third principal reflective value; and

determining that the dataform is darker than the background area if said second principal reflective value is most distinct from the third principal reflective value.

10. A method according to claim 1, wherein said dataform is one of a bar code and a matrix code.

11. A method for evaluating an image comprised of a plurality of pixels, and identifying characteristics of a dataform therein, the method comprising the steps of:

(a) sampling a section of an image, to obtain a plurality of reflective values respectively associated with the plurality of pixels;

(b) determining, for each said section of the image, the number of occurrences of each reflective value of said plurality of reflective values, wherein the number of occurrences are occurrence data;

(c) determining whether the derived occurrence data for the section of the image indicates first and second reflective values having a relatively high number of occurrences within said section of the image, or a single reflective value having a relatively high number of occurrences within said section of the image;

(d) repeating steps (a), (b) and (c) for one or more sections of the image;

(e) comparing the first and second reflective values to the single reflective value; and

(f) determining which of the first and second reflective values is most distinct from the single reflective value.

12. A method according to claim 11, wherein said step of determining the number of occurrences of each reflective value of said plurality of reflective values includes the step of obtaining a histogram.

13. A method according to claim 11, wherein each of said plurality of reflective values is indicative of a respective color.

14. A method according to claim 11, wherein said first reflective value is indicative of the presence of a first color, said second reflective value is indicative of the presence of a second color, and said single reflective value is indicative of the presence of a third color.

15. A method according to claim 14, wherein the presence of said first and second colors is indicative of a dataform, and the presence of said third color is indicative of a background area.

16. A method according to claim 15, wherein said first reflective value corresponds to a relatively dark color and said second reflective value corresponds to a relatively light color.

17. A method according to claim 16, wherein said method further comprises:

determining that the dataform is darker than the background area if said first value is most distinct from the single reflective value; and

determining that the dataform is lighter than the background area if said second reflective value is most distinct from the single reflective value.

18. A method according to claim 15, wherein said first reflective value corresponds to a relatively light color and said second reflective value corresponds to a relatively dark color.

19. A method according to claim 18, wherein said method further comprises:

determining that the dataform is lighter than the background area if said first reflective value is most distinct from the third reflective value; and

determining that the dataform is darker than the background area if said second reflective value is most distinct from the third reflective value.

20. A method according to claim 11, wherein said dataform is one of a bar code and a matrix code.

21. A method for evaluating an image including a dataform having elements, and a background area, the method comprising:

sampling a section of the image, to obtain a plurality of reflective values for one or more sections of the image, wherein said reflective values are indicative of a pixel color;

determining, for each said section of the image, the number of occurrences of each reflective value;

identifying the presence of a dataform and a background area, based upon the number of occurrences of each reflective value in each said section of the image, wherein said number of occurrences of each reflective value in each said section of the image are occurrence data;

determining whether the elements of the dataform have a color that is lighter or darker than the color of the background area; and

decoding said dataform.

22. A method according to claim 21, wherein said step of identifying the presence of a dataform and a background area includes:

determining whether the occurrence data for the section of the image indicates first and second reflective values having a relatively high number of occurrences within said section of the image, or a single reflective value having a relatively high number of occurrences within said section of the image.

23. A method according to claim 22, wherein said step of determining whether the elements of the dataform have a color that is lighter or darker than the color of the background area includes:

comparing the first and second reflective values to the single reflective value; and

determining which of the first and second reflective values is most distinct from the single reflective value.