# US 5,352,878 A · Method and apparatus for decoding bar code symbols using independent bar and space analysis > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,352,878 A - Document ID: US5352878A - Status: Granted - Kind: A - Application number: 08/011,458 - Filed: 1993-01-29 - Granted: 1994-10-04 - Earliest claimed: 1993-01-29 - Assignees: United Parcel Service of America, Inc. - Inventors: Christopher E. Smith; Mihael Klancnik - Web page: https://patentgrep.com/patent/US5352878A ## CPC - G06K 7/1443: {locating of the code in an image} - G06K 7/10851: {Circuits for pulse shaping, amplifying, eliminating noise signals, checking the function of the sensing device (basic electronic circuitry H03)} - G06K 7/14: using light without selection of wavelength, e.g. sensing reflected white light {(G06K7/10831 - G06K7/1097 take precedence)} - G06K 7/1465: {using several successive scans of the optical code} - G06K 7/1486: {Setting the threshold-width for bar codes to be decoded} - G06K: GRAPHICAL DATA READING (image or video recognition or understanding G06V); PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS ## Abstract A bar code reader decodes a bar code symbol, one character at a time, by analyzing the spaces of each character independently from the bars of each character. The reader determines the widths of each space and each bar. The reader then determines a space-width threshold based on the widths of the spaces and a bar-width threshold based on the widths of the bars. The reader then classifies each space as being either narrow or wide by comparing each space to the space-width threshold. The reader also classifies each bar as being either narrow or wide by comparing each bar to the bar-width threshold. The reader then decodes the character according to the narrow/wide classifications. ## Claims ### Claim 1 A method for decoding a character of a bar code symbol, wherein said character comprises one or more spaces and one or more bars, comprising the steps of: (a) scanning said symbol to determine the widths of said spaces and the widths of said bars; (b) determining a space-width threshold in accordance with said widths of said spaces; (c) determining a bar-width threshold in accordance with said widths of said bars, wherein said space-width threshold is different from said bar-width threshold; (d) comparing each of said spaces to said space-width threshold; (e) comparing each of said bars to said bar-width threshold; and (f) decoding said character in accordance with said comparisons of steps (d) and (e). ### Claim 2 (depends on 1) The method of claim 1, wherein: said space-width threshold is the average of the widest of said spaces and the narrowest of said spaces; said bar-width threshold is the average of the widest of said bars and the narrowest of said bars; step (d) comprises the step of comparing each of said spaces to said space-width threshold to determine whether each of said spaces is narrow or wide; and step (e) comprises the step of comparing each of said bars to said bar-width threshold to determine whether each of said bars is narrow or wide. ### Claim 3 (depends on 1) The method of claim 1, wherein said bar code symbol is a Code 39 symbol and said character comprises four spaces and five bars. ### Claim 4 (depends on 1) The method of claim 1, wherein said bar code symbol is an Interleaved Code 2 of 5 symbol and said character comprises five spaces and five bars. ### Claim 5 (depends on 1) The method of claim 1, wherein said bar code symbol is in a pixel image, and step (a) comprises the steps of: (1) generating a composite signal in accordance with said symbol; and (2) determining said widths of said spaces and said widths of said bars in accordance with said composite signal. ### Claim 6 (depends on 1) The method of claim 1, wherein said bar code symbol is in a pixel image, and step (a) comprises the steps of: (1) generating a whitening gradient signal and a blackening gradient signal in accordance with said symbol; and (2) determining said widths of said spaces and said widths of said bars in accordance with said whitening and blackening gradient signals. ### Claim 7 (depends on 1) The method of claim 1, wherein said bar code symbol is in a binary pixel image and further comprising the step of locating said symbol in said image using byte-based searching for a quiet zone of said symbol. ### Claim 8 (depends on 1) The method of claim 1, wherein said bar code symbol is in a binary pixel image and further comprising the step of locating said symbol in said image using byte-based searching for a plurality of bright/dark transitions of said symbol. ### Claim 9 An apparatus for decoding a character of a bar code symbol, wherein said character comprises one or more spaces and one or more bars, comprising: (a) means for scanning said symbol to determine the widths of said spaces and the widths of said bars; (b) means for determining a space-width threshold in accordance with said widths of said spaces; (c) means for determining a bar-width threshold in accordance with said widths of said bars, wherein said space-width threshold is different from said bar-width threshold; (d) means for comparing each of said spaces to said space-width threshold; (e) means for comparing each of said bars to said bar-width threshold; and (f) means for decoding said character in accordance with said comparisons of means (d) and (e). ### Claim 10 (depends on 9) The apparatus of claim 9, wherein: said space-width threshold is the average of the widest of said spaces and the narrowest of said spaces; said bar-width threshold is the average of the widest of said bars and the narrowest of said bars; means (d) comprises means for comparing each of said spaces to said space-width threshold to determine whether each of said spaces is narrow or wide; and means (e) comprises means for comparing each of said bars to said bar-width threshold to determine whether each of said bars is narrow or wide. ### Claim 11 (depends on 9) The apparatus of claim 9, wherein said bar code symbol is a Code 39 symbol and said character comprises four spaces and five bars. ### Claim 12 (depends on 9) The apparatus of claim 9, wherein said bar code symbol is an Interleaved Code 2 of 5 symbol and said character comprises five spaces and five bars. ### Claim 13 (depends on 9) The apparatus of claim 9, wherein said bar code symbol is in a pixel image, and means (a) comprises: (1) means for generating a composite signal in accordance with said symbol; and (2) means for determining said widths of said spaces and said widths of said bars in accordance with said composite signal. ### Claim 14 (depends on 9) The apparatus of claim 9, wherein said bar code symbol is in a pixel image, and means (a) comprises: (1) means for generating a whitening gradient signal and a blackening gradient signal in accordance with said symbol; and (2) means for determining said widths of said spaces and said widths of said bars in accordance with said whitening and blackening gradient signals. ### Claim 15 (depends on 9) The apparatus of claim 9, wherein said bar code symbol is in a binary pixel image and further comprising means for locating said symbol in said image using byte-based searching for a quiet zone of said symbol. ### Claim 16 (depends on 9) The apparatus of claim 9, wherein said bar code symbol is in a binary pixel image and further comprising means for locating said symbol in said image using byte-based searching for a plurality of bright/dark transitions of said symbol.