US 5,979,763 AGranted

Sub-pixel dataform reader with dynamic noise margins

AssigneeMetanetics Corporation

InventorsYnjiun P. Wang, Angi Ye

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Abstract

Sub-pixel processing of image data representing a dataform, such as a 2D bar code, enables reading of dataforms including more data/smaller elements, without costly increases in sensor and memory capacity. Whole pixel processing is employed for pixel-per-element resolutions of two or better. Sub-pixel cell edge transition location in image data is enhanced by use of a dynamically implemented noise margin applied with bands of gray scale values designated within the envelope of applicable gray scale maximum and minimum values. Sub-pixel cell edge transition location employs selection of transition segments (subject to the noise margin) and determination of a dynamic threshold for each relevant transition segment. The intersection of the threshold and the transition segment is then indicative of the location of the cell edge transition along a sampling line crossing the dataform. The process is repeated for successive cell edges along image data sampling lines and for additional sampling lines crossing successive rows of dataform elements. Run length data representing cell edge transition locations is constructed and usable for dataform decoding.

Claims18

Dependent claims

In a dataform reader, a method of locating dataform cell edge transitions in a reflected image of a dataform which includes high and low reflectance regions, comprising the steps of:

(a) acquiring a sequence of gray scale values for pixels representing a first sampling line crossing at least a first cell edge transition of said reflected image, and wherein said high and low reflectance regions are respectively represented within a high range of gray scale values and a low range of gray scale values, which are separated by a mid-range of gray scale values;
(b) selecting a transition segment having a segment magnitude value indicative of the difference in gray scale values between a specific local maximum gray scale value and a local minimum gray scale value of said sequence, which represent the ends of said segment;
(c) determining whether said transition segment meets the following criteria:
(i) said segment magnitude value exceeds a noise margin value;
and (ii) at least one of said local maximum and local minimum gray scale values is within said mid-range between said high and low ranges of gray scale values;
and
(d) if said transition segment meets at least one of said step (c) criteria, locating said first cell edge transition along said first sampling line by use of said transition segment and if neither criteria is met, not utilizing said transition segment for cell edge transition location.

4 more elements

In a dataform reader, a method of locating dataform cell edge transitions in a reflected image of a dataform which includes high and low reflectance regions comprising the steps of:

(a) acquiring a sequence of gray scale values for pixels representing a first sampling line crossing at least a first cell edge transition of said reflected image, and wherein said high and low reflectance regions are respectively represented within a high range of gray scale values and a low range of gray scale values, which are separated by a mid-range of such values;
(b) selecting a first window portion of said sequence;
(c) selecting borders of said high and low gray scale ranges for said first window section;
(d) selecting a transition segment having a segment magnitude value indicative of the difference in gray scale values between a specific local maximum gray scale value and a local minimum gray scale value of said sequence, which represent the ends of said segment;
(e) determining whether said transition segment meets the following criteria:
(i) said segment magnitude value exceeds a noise margin value and (ii) at least one of said local maximum and local minimum gray scale values is within said mid-range between said high and low ranges of gray scale values;
and
(f) if said transition segment meets at least one of said step (e) criteria, locating said first cell edge transition along said first sampling line by use of said transition segment and if neither criteria is met, not utilizing said transition segment for cell edge transition location.

5 more elements

Dependencies are inferred from the claim text.