LIST OF CONTENTS CHAPTER CONTENT PAGE DECLARATION DEDICATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK

Transcription

1 vii LIST OF CONTENTS CHAPTER CONTENT PAGE DECLARATION DEDICATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK LIST OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF NOTATIONS LIST OF ABBREVIATIONS LIST OF APPENDICES ii iii iv v vi vii x xi xiv xv xvi CHAPTER I INTRODUCTION Introduction Limitations of Conventional Barcode Readers Objectives Scope of Project Project Outline 6

2 CHAPTER II REVIEW OF LITERATURE STUDIES 8 viii 2.1 Introduction Barcode Readers Vision Based Barcode Readers Barcode Localization Barcode Reading The Anatomy of EAN-13 and UPC-A Barcode Size and Color Barcode Structure Encoding Check Digit Calculation Decoding 21 CHAPTER II I THEORETICAL BACKGROUND Introduction Imaging Devices Field of View & Angle of View Resolution Depth of View Lighting Distortion Blurring & Motion Tearing 38 CHAPTER IV ALGORITHMS & IMPLEMENTATIONS Introduction Overall System Design Preprocessing Grayscaling Filtering 43

3 ix Thresholding Decoding Scanning Barcode Identification & Extraction Decoding Height Extraction Algorithm Program Architecture 62 CHAPTER V RESULT Introduction Uneven Illumination, Shadow and Glare Barcode Orientation Tests on Various Object Shapes Multiple Barcodes in a Scene Product Comparison Recognition Rate/Accuracy Performance Comparison Discussion 88 CHAPTER VI CONCLUSION & SUMMARY Summary Conclusion Recommendations for Future Work 91 REFERENCES 93 APPENDIX 97

4 x LIST OF TABLES TABLE TITLE PAGE 2.1 Specification for EAN-13 & UPC-A barcodes Parity encoding table Character encoding table Approximation of FoV for various CCD sizes Type of illumination for different application requirements The normalization and rounding process Normal barcode (left to right) Flipped or mirrored barcode Height extraction reference table Feature comparison Test of accuracy 84-85

5 xi LIST OF FIGURES FIGURE TITLE PAGE 1.1 Common one-dimensional barcodes Two-dimensional barcodes, (a) 3-DI and (b) Array Tag, (c) 3 PDF417, (d) Data Matrix, (e) MaxiCode and (f) Aztec Code 2.1 Shows different types of barcode readers, (a) a Pen-type reader, 9 (b) a Laser scanner and (c) a CCD scanner 2.2 (a) UPC-A barcode, (b) equivalent EAN-13 barcode, with the 14 first character set to zero, and (c) an EAN-13 with an additional digit used 2.3 Actual sizes of EAN-13/UPC-A barcodes Encoding the number Comparison of AoV between a 25mm and a 35mm camera lens Projection of AoV and FoV in the horizontal and vertical 24 directions 3.3 Projection of FoV at a distance of do FoV for a (a) 35mm lens, (b) 25mm lens shows the amount of 26 information can be captured 3.5 Aspect ratio of various industry standard CCD sensors Nothing smaller than the physical size of two pixels can be 30 resolved. 3.7 DoV is larger when the aperture opening is small (large f-stop) DoV can be increased by adjusting the aperture Insufficient DoV will cause barcodes with odd placement 33 unreadable 3.10 DoV at various object-to-lens distances for 35mm and 25mm camera lens at f/1.3, f/2 and f/4 34

6 xii 3.11 Barcode inspection under (a) highly directional light source and 36 (b) diffuse lighting [20] 3.12 (a) Directional lighting, (b) diffuse lighting, (c) ring guide and 37 (d) diffuse axial lighting 3.13 Radial distortion on the KPC-S38CZV camera Motion tear Block diagram of project Spatial filters (a) Gaussian Blur, (b)laplacian (c) Sharpen (d) 43 Unsharpen Mask 4.3 (a) Global, (b) segmented, (c) local (Chow & Kanenko), (d) and 45 (e) algorithmic adaptive thresholding based on variance [23] 4.4 (a) Actual gray-level image, (b) manually selected global 47 threshold of 114, (c) global heuristic threshold, (d) local neighborhood of 5x5 with max-min threshold (e) local neighborhood (max-min) of 5x5 and Tg=3, (f) segment (heuristic) of 10x10 (g) segment (heuristic) of 10x10 with Tg=12 (h) algorithmic adaptive thresholding based on variance 4.5 Execution time of different thresholding methods on a 512x gray-level image 4.6 Scan directions implemented Skewed barcodes at different angles, where it is picked up by 50 several scan lines (a) horizontal and diagonal, (b) diagonal (c) vertical scan lines. 4.8 Steps to identify and extract the UPC-A and EAN-13 barcodes Predictive decoding tree for character determination Predictive tree to determine the symbology and the 1st character Performance comparison between predictive and exhaustive 60 decoding 4.12 Height extraction state machine Comparison between SISD and SIMD (MMX) architectures Program screenshot Program flowchart Barcode detection process 67

7 xiii 4.17 Scanning algorithm Quiet zone detection algorithm Algorithm for guard bars detection Checking the equality of the guard bars Algorithm for obtaining the height and width of a bar Algorithm for obtaining all the remaining bars of the EAN and UPC-A symbologies 4.23 The normalization process The error detection and correction process Shows how adaptive local thresholding is capable of 76 successfully thresholding an image which is affected by severe uneven illumination; (a) actual image affected by uneven illumination, (b) global thresholding, (c) local thresholding 5.2 Glare and shadowing on a specular surface Elimination of glare through local thresholding; (a) glare 78 affected region of a barcode, (b) missing bars due to global thresholding, (c) local thresholding able to recover missing bars (d) successful decoding process 5.4 Barcodes at different orientation (angle) Barcode orientation on (a) flat surfaces, (b) along the 80 circumference of a cylinder or curved object, (c) along the axis of a cylinder, and (d) on irregular surfaces 5.6 Barcodes on flat surfaces Barcodes on the circumference of cylinders Barcodes along the axis of cylinders Barcodes on irregular surfaces Successful detection of multiple barcodes in one scene Recognition accuracy Decoding time for a 512x512px color image The importance of optimal thresholding 89

8 xiv LIST OF NOTATIONS a c d i d o f H h ccd h i h o T T g T o w ccd w i w o θ h θ w Lens aperture (f-stop) Diameter of circle of confusion. Distance from the image plane to the optical center of the lens Distance from the object plane to the optical center of the lens Focal length Hyperfocal distance Height of CCD in pixels Height of image in millimeters Height of object in millimeters Threshold value Global threshold value Threshold Convergence factor Width of CCD in pixels Width of image in millimeters Width of the object in millimeters Vertical angle of view Horizontal angle of view

9 xv LIST OF ABREVIATIONS AoV BMP BPNN CCD CMOS CoC DoV EAN FF FoV FPS ISBN LUT MLP MMX NF PCI PDA px RBF RGBA SIMD SSE UPC Angle of View Windows Bitmap Back Propagation Neural Network Charge-Coupled Device Complementary Metal Oxide Semi-Conductor Circle of Confusion Depth of View European Article Number Far-Field Field of View Frames per Second International Standard Book Number Look-up Table Multi Layer Perceptron MultiMedia extension Near-Field Peripheral Component Interface Personal Digital Assistant Pixel Radial Basis Function Red-Green- Blue-Alpha Single Instruction Multiple Data Streaming SIMD Extensions Universal Product Code

10 xvi LIST OF APPENDICES APPENDIX TITLE PAGE A System Specification 97 B Scan Profiles 99 C C++ Class Declaration 100 D Test Images 110 E Results 112 F Screenshots of Commercial Test Programs 117