barcodes - CS 1 with Robots Decoding Barcodes Institute for...

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Unformatted text preview: CS 1 with Robots Decoding Barcodes Institute for Personal Robots in Education (IPRE) Aug 29 2007 2 Barcodes are designed to be machine readable They encode numbers and symbols using black and white bars. The examples on this page are standard 1D barcodes using the Code39 encoding scheme. Usually read by laser scanners, they can also be read using a camera. Aug 29 2007 3 Code39 (Sometimes called 3 from 9) barcodes use 9 bars to represent each symbol. The bars can be black or white. The bars are either narrow or wide. Wide bars must be 2.1 to 3 times larger than narrow bars. Each symbol pattern starts and ends with a black bar. A valid barcode starts and ends with the STAR (*) symbol, which is used as a delimiter. The STAR (*) symbol is made up of a narrow black bar, a wide white bar, a narrow black bar, a narrow white bar, a wide black bar, a narrow white bar, a wide black bar, a narrow white bar, and a narrow black bar. Aug 29 2007 4 Code39 (Sometimes called 3 from 9) barcodes use 9 bars to represent each symbol. The bars can be black or white. The bars are either narrow or wide. Wide bars must be 2.1 to 3 times larger than narrow bars. Each symbol pattern starts and ends with a black bar. A valid barcode starts and ends with the STAR (*) symbol, which is used as a delimiter. This could also be represented as the string bWbwBwBwb Aug 29 2007 5 How many bars is in a barcode that encodes 3 symbols? Although each symbol pattern starts and ends with a black bar, patterns must be separated by a white bar (typically narrow), so each symbol except the last is represented with 10 bars in total. (The last symbol has 9 bars, and does not need a separator after it.) Don't forget the Start and Stop symbol! Aug 29 2007 6 How many bars is in a barcode that encodes 3 symbols? Although each symbol pattern starts and ends with a black bar, patterns must be separated by a white bar (typically narrow), so each symbol except the last is represented with 10 bars in total. (The last symbol has 9 bars, and does not need a separator after it.) Don't forget the Start and Stop symbol! 3 symbols + start + stop = 5 symbols, at 9 bars each, plus 4 narrow white bars to separate the symbols is 9 * 5 + 4, or 10*5 1 to make 49 bars total! Aug 29 2007 7 All of the symbol patterns: What symbol is on the right? Aug 29 2007 8 It's an I What symbol is on the right? Aug 29 2007 9 But what does a barcode look like from the robot? The robot's camera has relatively low resolution (256x192 pixels). To decode a barcode successfully from an image, we need multiple pixels for each bar . This means that we are limited in the size of barcodes we can successfully use. Here is a picture of a two symbol (4 patterns total) barcode taken with a (VERY) carefully aimed robot camera: Aug 29 2007 10 It's sort of messy!...
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This note was uploaded on 01/25/2012 for the course CS 1301 taught by Professor Staff during the Fall '08 term at Georgia Institute of Technology.

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barcodes - CS 1 with Robots Decoding Barcodes Institute for...

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