Preface |
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xv | |
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xvii | |
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1 | (20) |
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Why do we process images? |
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1 | (1) |
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1 | (1) |
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What is the brightness of an image at a pixel position? |
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2 | (1) |
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Why are images often quoted as being 512 x 512, 256 x 256, 128 x 128 etc? |
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2 | (1) |
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How many bits do we need to store an image? |
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2 | (1) |
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What is meant by image resolution? |
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2 | (4) |
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How do we do Image Processing? |
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6 | (1) |
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What is a linear operator? |
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6 | (1) |
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How are operators defined? |
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6 | (1) |
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How does an operator transform an image? |
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6 | (1) |
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What is the meaning of the point spread function? |
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7 | (2) |
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How can we express in practice the effect of a linear operator on an image? |
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9 | (5) |
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What is the implication of the separability assumption on the structure of matrix H? |
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14 | (1) |
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How can a separable transform be written in matrix form? |
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15 | (1) |
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What is the meaning of the separability assumption? |
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15 | (3) |
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What is the ``take home'' message of this chapter? |
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18 | (1) |
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What is the purpose of Image Processing? |
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18 | (1) |
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18 | (3) |
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21 | (68) |
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What is this chapter about? |
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21 | (1) |
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How can we define an elementary image? |
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21 | (1) |
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What is the outer product of two vectors? |
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21 | (1) |
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How can we expand an image in terms of vector outer products? |
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21 | (2) |
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What is a unitary transform? |
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23 | (1) |
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What is a unitary matrix? |
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23 | (1) |
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What is the inverse of a unitary transform? |
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24 | (1) |
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How can we construct a unitary matrix? |
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24 | (1) |
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How should we choose matrices U and V so that g can be represented by fewer bits than f? |
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24 | (1) |
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How can we diagonalize a matrix? |
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24 | (6) |
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How can we compute matrices U, V and A1/2 needed for the image diagonalization? |
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30 | (4) |
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What is the singular value decomposition of an image? |
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34 | (1) |
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How can we approximate an image using SVD? |
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34 | (1) |
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What is the error of the approximation of an image by SVD? |
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35 | (1) |
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How can we minimize the error of the reconstruction? |
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36 | (1) |
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What are the elementary images in terms of which SVD expands an image? |
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37 | (8) |
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Are there any sets of elementary images in terms of which ANY image can be expanded? |
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45 | (1) |
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What is a complete and orthonormal set of functions? |
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45 | (1) |
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Are there any complete sets of orthonormal discrete valued functions? |
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46 | (1) |
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How are the Haar functions defined? |
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46 | (1) |
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How are the Walsh functions defined? |
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47 | (1) |
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How can we create the image transformation matrices from the Haar and Walsh functions? |
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47 | (4) |
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What do the elementary images of the Haar transform look like? |
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51 | (6) |
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Can we define an orthogonal matrix with entries only + 1 or - 1? |
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57 | (1) |
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What do the basis images of the Hadamard/Walsh transform look like? |
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57 | (5) |
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What are the advantages and disadvantages of the Walsh and the Haar transforms? |
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62 | (1) |
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What is the Haar wavelet? |
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62 | (1) |
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What is the discrete version of the Fourier transform? |
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63 | (2) |
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How can we write the discrete Fourier transform in matrix form? |
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65 | (1) |
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Is matrix U used for DFT unitary? |
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66 | (2) |
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Which are the elementary images in terms of which DFT expands an image? |
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68 | (4) |
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Why is the discrete Fourier transform more commonly used than the other transforms? |
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72 | (1) |
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What does the convolution theorem state? |
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72 | (7) |
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How can we display the discrete Fourier transform of an image? |
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79 | (1) |
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What happens to the discrete Fourier transform of an image if the image is rotated? |
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79 | (2) |
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What happens to the discrete Fourier transform of an image if the image is shifted? |
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81 | (1) |
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What is the relationship between the average value of a function and its DFT? |
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82 | (1) |
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What happens to the DFT of an image if the image is scaled? |
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83 | (3) |
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What is the discrete cosine transform? |
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86 | (1) |
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What is the ``take home'' message of this chapter? |
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86 | (3) |
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Statistical Description of Images |
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89 | (36) |
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What is this chapter about? |
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89 | (1) |
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Why do we need the statistical description of images? |
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89 | (1) |
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Is there an image transformation that allows its representation in terms of uncorrelated date that can be used to approximate the image in the least mean square error sense? |
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89 | (1) |
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90 | (1) |
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What is a random variable? |
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90 | (1) |
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How do we describe random variables? |
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90 | (1) |
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What is the probability of an event? |
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90 | (1) |
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What is the distribution function of a random variable? |
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90 | (1) |
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What is the probability of a random variable taking a specific value? |
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91 | (1) |
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What is the probability density function of a random variable? |
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91 | (1) |
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How do we describe many random variables? |
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92 | (1) |
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What relationships may n random variables have with each other? |
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92 | (1) |
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How do we then define a random field? |
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93 | (1) |
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How can we relate two random variables that appear in the same random field? |
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94 | (1) |
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How can we relate two random variables that belong to two different random fields? |
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95 | (1) |
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Since we always have just one version of an image how do we calculate the expectation values that appear in all previous definitions? |
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96 | (1) |
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When is a random field homogeneous? |
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96 | (1) |
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How can we calculate the spatial statistics of a random field? |
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97 | (1) |
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When is a random field ergodic? |
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97 | (1) |
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When is a random field ergodic with respect to the mean? |
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97 | (1) |
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When is a random field ergodic with respect to the autocorrelation function? |
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97 | (5) |
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What is the implication of ergodicity? |
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102 | (1) |
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How can we exploit ergodicity to reduce the number of bits needed for representing an image? |
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102 | (1) |
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What is the form of the autocorrelation function of a random field with uncorrelated random variables? |
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103 | (1) |
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How can we transform the image so that its autocorrelation matrix is diagonal? |
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103 | (1) |
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Is the assumption of ergodicity realistic? |
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104 | (6) |
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How can we approximate an image using its K-L transform? |
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110 | (1) |
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What is the error with which we approximate an image when we truncate its K-L expansion? |
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110 | (1) |
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What are the basis images in terms of which the Karhunen-Loeve transform expands an image? |
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111 | (13) |
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What is the ``take home'' message of this chapter? |
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124 | (1) |
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125 | (30) |
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What is image enhancement? |
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125 | (1) |
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How can we enhance an image? |
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125 | (1) |
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Which methods of the image enhancement reason about the grey level statistics of an image? |
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125 | (1) |
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What is the histogram of an image? |
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125 | (1) |
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When is it necessary to modify the histogram of an image? |
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126 | (1) |
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How can we modify the histogram of an image? |
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126 | (1) |
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What is histogram equalization? |
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127 | (1) |
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Why do histogram equalization programs usually not produce images with flat histograms? |
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127 | (1) |
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Is it possible to enhance an image to have an absolutely flat histogram? |
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127 | (2) |
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What if we do not wish to have an image with a flat histogram? |
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129 | (1) |
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Why should one wish to perform something other than histogram equalization? |
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130 | (1) |
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What is the image has inhomogeneous contrast? |
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131 | (1) |
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Is there an alternative to histogram manipulation? |
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132 | (3) |
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How can we improve the contrast of a multispectral image? |
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135 | (1) |
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What is principal component analysis? |
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136 | (1) |
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What is the relationship of the Karhunen-Loeve transformation discussed here and the one discussed in Chapter 3? |
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136 | (1) |
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How can we perform principal component analysis? |
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137 | (1) |
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What are the advantages of using principal components to express an image? |
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138 | (1) |
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What are the disadvantages of principal component analysis? |
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138 | (6) |
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Some of the images with enhanced contrast appear very noisy. Can we do anything about that? |
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144 | (1) |
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What are the types of noise present in an image? |
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144 | (2) |
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What is a rank order filter? |
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146 | (1) |
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What is median filtering? |
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146 | (1) |
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What if the noise in an image is not impulse? |
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146 | (1) |
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Why does lowpass filtering reduce noise? |
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147 | (1) |
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What if we are interested in the high frequencies of an image? |
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148 | (1) |
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What is the ideal highpass filter? |
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148 | (1) |
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How can we improve an image which suffers from variable illumination? |
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148 | (3) |
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Can any of the objectives of image enhancement be achieved by the linear methods we learned in Chapter 2? |
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151 | (2) |
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What is the ``take home'' message of this chapter? |
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153 | (2) |
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155 | (38) |
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What is this chapter about? |
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155 | (1) |
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How do we define a 2D filter? |
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155 | (1) |
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How are the system function and the unit sample response of the filter related? |
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155 | (2) |
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Why are we interested in the filter function in the real domain? |
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157 | (1) |
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Are there any conditions which h(k,l) must fulfil so that it can be used as a convolution filter? |
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157 | (4) |
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What is the relationship between the 1D and the 2D ideal lowpass filters? |
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161 | (1) |
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How can we implement a filter of infinite extent? |
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161 | (1) |
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How is the z-transform of a digital 1D filter defined? |
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161 | (2) |
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Why do we use z-transforms? |
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163 | (1) |
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How is the z-transform defined in 2D? |
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163 | (7) |
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Is there any fundamental difference between 1D and 2D recursive filters? |
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170 | (1) |
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How do we know that a filter does not amplify noise? |
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171 | (1) |
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Is there an alternative to using infinite impulse response filters? |
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171 | (1) |
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Why do we need approximation theory? |
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171 | (1) |
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How do we know how good an approximate filter is? |
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171 | (1) |
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What is the best approximation to an ideal given system function? |
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171 | (1) |
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Why do we judge an approximation according to the Chebyshev norm instead of the square error? |
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172 | (1) |
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How can we obtain an approximation to a system function? |
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172 | (1) |
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172 | (1) |
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What is wrong with windowing? |
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173 | (1) |
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How can we improve the result of the windowing process? |
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173 | (1) |
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Can we make use of the windowing functions that have been developed for 1D signals, to define a windowing function for images? |
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173 | (1) |
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What is the formal definition of the approximation problem we are trying to solve? |
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173 | (1) |
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What is linear programming? |
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174 | (1) |
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How can we formulate the filter design problem as a linear programming problem? |
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174 | (5) |
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Is there any way by which we can reduce the computational intensity of the linear programming solution? |
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179 | (1) |
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What is the philosophy of the iterative approach? |
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179 | (1) |
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Are there any algorithms that work by decreasing the upper limit of the fitting error? |
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180 | (1) |
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How does the maximizing algorithm work? |
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180 | (1) |
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What is a limiting set of equations? |
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180 | (1) |
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What does the La Vallee Poussin theorem say? |
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180 | (1) |
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What is the proof of the La Vallee Poussin theorem? |
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181 | (1) |
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What are the steps of the iterative algorithm? |
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181 | (1) |
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Can we approximate a filter by working fully in the frequency domain? |
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182 | (1) |
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How can we express the system function of a filter at some frequencies as a function of its values at other frequencies? |
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182 | (7) |
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What exactly are we trying to do when we design the filter in the frequency domain only? |
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189 | (1) |
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How can we solve for the unknown values H(k, l)? |
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190 | (1) |
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Does the frequency sampling method yield optimal solutions according to the Chebyshev criterion? |
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190 | (2) |
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What is the ``take home'' message of this chapter? |
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192 | (1) |
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193 | (72) |
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What is image restoration? |
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193 | (1) |
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What is the difference between image enhancement and image restoration? |
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193 | (1) |
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Why may an image require restoration? |
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193 | (1) |
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How may geometric distortion arise? |
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193 | (1) |
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How can a geometrically distorted image be restored? |
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193 | (1) |
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How do we perform the spatial transformation? |
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194 | (1) |
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Why is grey level interpolation needed? |
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195 | (3) |
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How does the degraded image depend on the undegraded image and the point spread function of a linear degradation process? |
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198 | (1) |
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How does the degraded image depend on the undegraded image and the point spread function of a linear shift invariant degradation process? |
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198 | (1) |
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What form does equation (6.5) take for the case of discrete images? |
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199 | (1) |
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What is the problem of image restoration? |
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199 | (1) |
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How can the problem of image restoration be solved? |
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199 | (1) |
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How can we obtain information on the transfer function H(u, v) of the degradation process? |
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199 | (10) |
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If we know the transfer function of the degradation process, isn't the solution to the problem of image restoration trivial? |
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209 | (1) |
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What happens at points (u, v) where H(u, v) = 0? |
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209 | (1) |
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Will the zeroes of H(u, v) and G(u, v) always coincide? |
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209 | (1) |
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How can we take noise into consideration when writing the linear degradation equation? |
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210 | (1) |
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How can we avoid the amplification of noise? |
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210 | (7) |
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How can we express the problem of image restoration in a formal way? |
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217 | (1) |
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What is the solution of equation (6.37)? |
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217 | (1) |
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Can we find a linear solution to equation (6.37)? |
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217 | (1) |
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What is the linear least mean square error solution of the image restoration problem? |
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218 | (1) |
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Since the original image f(r) is unknown, how can we use equation (6.41) which relies on its cross-spectral density with the degraded image, to derive the filter we need? |
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218 | (1) |
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How can we possibly use equation (6.47) if we know nothing about the statistical properties of the unknown image f(r)? |
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219 | (1) |
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What is the relationship of the Wiener filter (6.47) and the inverse filter of equation (6.25)? |
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219 | (1) |
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Assuming that we know the statistical properties of the unknown image f(r), how can we determine the statistical properties of the noise expressed by Svv(r)? |
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220 | (10) |
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If the degradation process is assumed linear, why don't we solve a system of linear equations to reverse its effect instead of invoking the convolution theorem? |
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230 | (1) |
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Equation (6.76) seems pretty straightforward, why bother with any other approach? |
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231 | (1) |
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Is there any way by which matrix H can be inverted? |
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232 | (1) |
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When is a matrix block circulant? |
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232 | (1) |
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When is a matrix circulant? |
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232 | (1) |
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Why can block circulant matrices be inverted easily? |
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233 | (1) |
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Which are the eigenvalues and the eigenvectors of a circulant matrix? |
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233 | (1) |
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How does the knowledge of the eigenvalues and the eigenvectors of a matrix help in inverting the matrix? |
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234 | (5) |
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How do we know that matrix H that expresses the linear degradation process is block circulant? |
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239 | (1) |
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How can we diagonalize a block circulant matrix? |
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240 | (10) |
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OK, now we know how to overcome the problem of inverting H; however, how can we overcome the extreme sensitivity of equation (6.76) to noise? |
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250 | (1) |
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How can we incorporate the constraint in the inversion of the matrix? |
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251 | (2) |
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What is the relationship between the Wiener filter and the constrained matrix inversion filter? |
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253 | (9) |
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What is the ``take home'' message of this chapter? |
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262 | (3) |
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Image Segmentation and Edge Detection |
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265 | (60) |
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What is this chapter about? |
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265 | (1) |
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What exactly is the purpose of image segmentation and edge detection? |
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265 | (1) |
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How can we divide an image into uniform regions? |
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265 | (1) |
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What do we mean by ``labelling'' an image? |
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266 | (1) |
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What can we do if the valley in the histogram is not very sharply defined? |
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266 | (1) |
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How can we minimize the number of misclassified pixels? |
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267 | (1) |
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How can we choose the minimum error threshold? |
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268 | (5) |
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What is the minimum error threshold when object and background pixels are normally distributed? |
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273 | (1) |
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What is the meaning of the two solution of (7.6)? |
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274 | (4) |
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What are the drawbacks of the minimum error threshold method? |
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278 | (1) |
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Is there any method that does not depend on the availability of models for the distribution of the object and the background pixels? |
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278 | (4) |
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Are there any drawbacks to Otsu's method? |
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282 | (1) |
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How can we threshold images obtained under variable illumination? |
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282 | (1) |
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If we threshold the image according to the histogram of In f(x, y), are we thresholding it according to the refectance properties of the imaged surfaces? |
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283 | (2) |
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Since straghtforward thresholding methods break down under variable illumination, how can we cope with it? |
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285 | (2) |
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Are there any shortcomings of the thresholding methods? |
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287 | (1) |
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How can we cope with images that contain regions that are not uniform but they are perceived as uniform? |
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288 | (1) |
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Are there any segmentation methods that take into consideration the spatial proximity of pixels? |
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288 | (1) |
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How can one choose the seed pixels? |
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288 | (1) |
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How does the split and merge method work? |
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288 | (1) |
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Is it possible to segment an image by considering the dissimilarities between regions, as opposed to considering the similarities between pixels? |
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289 | (1) |
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How do we measure the dissimilarity between neighbouring pixels? |
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289 | (1) |
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What is the smallest possible window we can choose? |
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290 | (1) |
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What happens when the image has noise? |
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291 | (3) |
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How can we choose the weights of a 3 x 3 mask for edge detection? |
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294 | (2) |
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What is the best value of parameter K? |
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296 | (7) |
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In the general case, how do we decide whether a pixel is an edge pixel or not? |
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303 | (3) |
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Are Sobel masks appropriate for all images? |
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306 | (1) |
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How can we choose the weights of the mask if we need a larger mask owing to the presence of significant noise in the image? |
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306 | (3) |
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Can we use the optimal filters for edges to detect lines in an image in an optimal way? |
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309 | (1) |
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What is the fundamental difference between step edges and lines? |
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309 | (13) |
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What is the ``take home'' message of this chapter? |
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322 | (3) |
Bibliography |
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325 | (4) |
Index |
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329 | |