Image Acquisitionand Proces

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Image Analysis 213 FIGURE 7.72 Lines intersection example — wiring diagram. 7.9.3 LINE FITTING Fitting is a useful mathematical technique when used to discover trends in sample data sets, and can be just as valuable when examining images. Parts under inspection often contain regular repeating structures, and line Þtting can be used as a quality control measure to ensure that parts are consistent. Consider Figure 7.73: A series of Australian ßags has been printed on a sheet, although one of the ßags has been printed with an incorrect alignment. FIGURE 7.73 Fit line example. Using IMAQ Count Objects and IMAQ Fit Line, it is obvious that the third ßag from the left is not in the correct position. The Federation star (the seven-pointed star in the bottom left quadrant of the ßag) has been detected, and their centers determined. This data has been then passed to IMAQ Fit Line, which determined the line of best Þt. Features that are outside of a user-deÞned range of distances from the Þtted line can then be regarded as inappropriate, and the part is failed (Figure 7.74). IMAQ Fit Line does not perform a line of best Þt in the true mathematical sense, as it can disregard some points that you include in the set to be considered. You are able to deÞne a pixel radius that deÞnes a corridor either side of the line of best Þt, where only points within the corridor are considered. IMAQ Fit Line Þnds the line of best Þt by Þrst considering a subset of points that has been deÞned, and subsequently calculating the mean square distance (MSD) of this line (Figure 7.75).
214 Image Acquisition Processing with LabVIEW FIGURE 7.74 Fit line example — wiring diagram. d 0 Points Considered in this Set d 1 d 2 d 3 d... Points not Considered in this Set d n Line of Best Fit FIGURE 7.75 Line of best Þt determination. The mean square distance is calculated using the following equation: MSD n 1 Âd 2 a a 0 n = = - Once the MSD has been calculated, a new line of best Þt is determined using a different set of points, and its MSD is also calculated. This process is repeated until all of the points in the input dataset have been considered (except those discarded for lying outside of the pixel radius range), and the set with the lowest MSD is returned as the line of best Þt. The MSD approach of line Þtting was selected to minimize the impact of outlying points. Consider the parallel rake application shown in Figure 7.76. If the application requirement is to Þt a line to the edge of the spanner head blade, the four extreme right detected edge coordinates are erroneous, although they are perfectly valid detected edges, they do not form part of the feature that we are looking for, and are ignored if the IMAQ Fit Line parameters are set appropriately. 7.9.4 CIRCLE AND ELLIPSE FITTING If you are searching an image for a regular feature, it is often much faster to use a rake and reconstruct shapes from the detected edges rather than using a pattern match template. If you want either a circle or ellipse, the IMAQ Fit Circle and IMAQ Fit Ellipse analytical geometric tools can be helpful. IMAQ Fit Circle requires a minimum of three points to function, although extra valid points will increase its accuracy.
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IMAGE PROCESSING SERIES Series Edit
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Foreword The introduction of LabVIE
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FIGURE 1 Vision 6.1 FIGURE 2 Compan
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Acknowledgments My gratitude goes o
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Dedication To Don “old fella” P
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Contents Chapter 1 Image Types and
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Chapter 4 Displaying Images........
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Chapter 7 Image Analysis...........
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1 Image Types and File Management F
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Image Types and File Management 3 F
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Image Types and File Management 5 A
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Image Types and File Management 7 C
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Image Types and File Management 9 p
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Image Types and File Management 11
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Image Types and File Management 13
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2 Setting Up You should never under
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Setting Up 17 FIGURE 2.3 (a) Interl
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Setting Up 19 Linear Aray Light Sou
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Setting Up 21 FIGURE 2.7 National I
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Setting Up 23 2.1.3.2 Control and I
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Setting Up 25 FIGURE 2.11 X-Ray ima
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Setting Up 27 Apple Computer techno
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Setting Up 29 FIGURE 2.17 An inexpe
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Setting Up 31 Although this would b
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Setting Up 33 134 -115 \ Contrast =
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Setting Up 35 resolution printer wi
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Setting Up 37 C A B C Traditional T
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Setting Up 39 Camera Light Source O
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Setting Up 41 Camera Light Source (
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Setting Up 43 FIGURE 2.37 (a) An ob
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Setting Up 45 FIGURE 2.41 (a) PCB p
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6 Morphology When applied to vision
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Morphology 143 I Closed { } = Erode
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Morphology 145 FIGURE 6.3 Simple mo
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Morphology 147 FIGURE 6.5 Custom st
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Morphology 149 FIGURE 6.8 Particle
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Morphology 151 FIGURE 6.12 Fill hol
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Morphology 153 FIGURE 6.17 Danielss
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Morphology 155 Detected circles wit
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Morphology 157 6.5 CASE STUDY: FIND
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Morphology 159 6.6 USER SOLUTION: D
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Morphology 161 ULTRASOUND MACHINE (
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