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Machine Vision
Published in Jerry C. Whitaker, Microelectronics, 2018
David A. Kosiba, Rangachar Kasturi
One of the earliest methods for representing a boundary uses directional codes, called chain codes. The object boundary is resampled at an appropriate scale, and an ordered list of points along the boundary is represented by a string of directions codes (see Fig. 19.9(a)). Often to retain all of the information in the boundary, the resampling step is bypassed. However, resampling eliminates minor fluctuations that typically are due to noise. Chain codes possess some attractive features; namely, the rotation of an object by multiples of 45° is easily implemented; the derivative of the chain code, the difference code obtained by computing the first differences of the chain code, is rotation invariant; and other characteristics of a region, such as area and corners, can be computed directly from the chain code. The limitations of this representation method are attributed to the restricted directions used to represent the tangent at a point. Although codes with larger numbers of directions are occasionally used, the eight-directional chain code is the most commonly used.
Two-Dimensional Measurements (Part 2)
Published in F. Brent Neal, John C. Russ, Measuring Shape, 2017
This limitation encourages other approaches to the unrolling instead of plotting radius from the centroid. One of the common ways of encoding an object in image analysis software uses “chain code,” introduced in Chapter 2 in Figure 2.45. As shown in Figure 4.15, this is a series of digits that record the path from pixel to pixel along the perimeter. Plotting the string of digits produces a graph that also repeats for every circumnavigation and might be subjected to Fourier analysis. But because of the discontinuity between direction 1 and direction 8, this graph is not suitable. The solution is to use differential chain code. Instead of plotting the absolute direction of each link in the chain, changes in direction are plotted. If the chain continues in the same direction, a value of zero is assigned. Values of +1 or +2 represent turns to the right, while –1 and –2 represent turns to the left.
Applications of Random Signal Processing
Published in Shaila Dinkar Apte, Random Signal Processing, 2017
Chain Code Method: The histogram of chain code feature extracts the information about the pixel distribution in different directions, which captures the shape of characters produced in the writing, slant, vertical strokes present, and roundness. The implementation steps are given in Figure 10.10a. The original image is converted into binary image. Then, the connected components and their boundaries are detected. The boundaries are labeled with freeman chain code using directions and values given in table as shown in Figure 10.10b. The example of boundary labeling is shown in Figure 10.10c.
Recognition of Kannada Character Scripts Using Hybrid Feature Extraction and Ensemble Learning Approaches
Published in Cybernetics and Systems, 2023
Supreetha Patel Tiptur Parashivamurthy, Sannangi Viswaradhya Rajashekararadhya
The chain Code Histogram technique (Boukharouba and Bennia 2017) is considered the statistical technique for determining the direction of the digit contour. It extracts the boundary features of shape, corners, and perimeters. Moreover, this technique is utilized to speed up the training process. Consequently, it helps to eliminate the overfitting risk reduction. This model has computed the slope among the two successive points that provides the angle generated through the line joining them. Further, the group of slopes (0°, 45°, 90°, 135°) is identically showed at the directions (180°, 225°, 270°, 315°). Hence, four direction codes are allocated for every two associated pixels. For acquiring the features over the character contour, the histogram of 4-chain code directions is applied. The 4-bin histogram belonging to the chain code directions is determined, in which every bin indicates the frequency of a single direction. Further, the feature vector of the contour is composed of 9 × 4(36) number of components that are gotten into normalization. The components belonging to the feature vector is shown by that depicted in Eq. (14).
Structural feature analysis of the vascular network in retinal images
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2019
O. Bandyopadhyay, T. Dutta, N. Dutta, A. Biswas, B. B. Bhattacharya
Chain Code [Freeman (1961)]: It is used to encode a direction around the border between pixels. If G(m, n) is a grid point, then the grid point is a neighbour of G, provided that . The chain code of G with respect to its neighbouring grid point in can have a value as shown in Figure 1(a).