Thesis (PDF) - Signal & Image Processing Lab

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98 CHAPTER 6. EXTREMA-WATERSHED TREE EXAMPLE Figure 6.26: Traditional pseudo-dual open-close and close-open operators. Figure 6.27: Median operator compared to the self-dual opening using Extrema watershed tree.
6.4. APPLICATION EXAMPLES 99 6.4 Application examples A common usage of opening and opening by reconstruction operators is cleaning noisy images as an intermediate step in various applications. Our operators, defined on extrema watershed tree, have an important feature: duality. In the next paragraphs we will show a number of possible applications that may use the EWT-based filtering as an intermediate step. The presented applications are OCR (Optical Character Recognition) algorithms and dust and scratch removal from images. 6.4.1 Pre-processing for car license plate number recognition Morphological operators are a common choice for applications that require image simplification. One kind of such an application is pre-processing for OCR (Optical Character Recognition) algorithms. We have chosen a specific OCR algorithm, used for recognition of license plate numbers, that was developed in [25]. This algorithm uses a mask for each digit and looks for the best correlation among these masks with an image. Any noise that exists in the image degrades the correlation value and interferes with the recognition. This particular algorithm has an important benefit: it calculates a coefficient of recognition quality. This coefficient enables us to measure recognition improvements, when using different pre-processing algorithms. The exact definition of this coefficient is presented in [25]. Consider an example license plate shown in Fig. 6.29. This image is corrupted with different kinds of noise, see Fig. 6.30. The correlation is done on the gray scale image shown in Fig. 6.31. It is difficult to automatically recognize the numbers without pre- processing, because of the noise level. We have done opening by reconstruction, using the structuring element shown in Fig. 6.28. The diameter of this SE is equal to the width of digits lines. This size of SE assures that we filter as much noise as possible without damage to the numbers. The resulting image can be seen in Fig. 6.32. In this figure, almost all the noise is gone, and the image is much clearer and suitable for OCR. The effect of the proposed pre-processing can be seen in table 6.1. Without the pre-processing, the OCR failed to recognize correctly the plate number. The pre- processing, not only removes the noise, but also simplifies the image. Therefore, when
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SELF-DUAL MORPHOLOGICAL OPERATORS B
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The Research Thesis was done under
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iv CONTENTS 3 Implementation of BTV
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List of Tables 2.1 The BTV transfor
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viii LIST OF FIGURES 2.9 An example
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x LIST OF FIGURES 4.17 A Simba imag
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xii LIST OF FIGURES 6.20 A Lena ima
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Abstract This research addresses a
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4 List of Abbreviations and Symbols
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6 CHAPTER 1. INTRODUCTION the image
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8 CHAPTER 1. INTRODUCTION disadvant
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10 CHAPTER 1. INTRODUCTION 3. A gen
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Chapter 2 Theoretical Background 2.
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14 CHAPTER 2. THEORETICAL BACKGROUN
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38 CHAPTER 3. IMPLEMENTATION OF BTV
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Chapter 4 The “trench” problem
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46CHAPTER 4. THE “TRENCH” PROBL
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Page 130 and 131: Bibliography [1] J. Serra, Image An
Page 132: 118 BIBLIOGRAPHY [21] Renato Keshet
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