Image Acquisitionand Proces

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Image Analysis 201 FIGURE 7.54 Pixel coordinates array. A B C D E F Pixel Intensity Contrast Distance Along ROI Path FIGURE 7.55 Example ROI path intensity plot. 7.7.4 USING THE CALIPER TOOL TO MEASURE FEATURES IMAQ Edge Tool is very useful in Þnding edges along a ROI, but it is then up to the programmer to parse the returned information and attempt to understand what the edges mean with respect to the image. IMAQ Caliper Tool is able to detect and classify edge pairs, which are two consecutive edges with opposite polarities. Consider the line ROI intensity plot in Figure 7.55. Edges exist (noted A through F), and can be classiÞed using their polarities (A, C and E have a polarity of 1, whereas the polarities of B, D and F are –1). Using IMAQ Caliper Tool, the distances between the polarity pairs (AB, CD and EF) can be measured. Consider the example in Figure 7.56. Not only have the obvious primary edge pairs been detected and measured, data concerning secondary pairs (pairs containing voids) has also been considered. Considering the ROI intensity plot in Figure 7.55, the primary pairs are AB, CD and EF, and the secondary pairs are AD, AF and CF. DeÞning the edge parameters in the same way as IMAQ Edge Tool, the caliper parameters conÞgures IMAQ Caliper Tool. The caliper parameters cluster contains three elements: polarity, separation and separation deviation (Table 7.5). The example in Figure 7.56 was achieved using the code shown in Figure 7.57. After IMAQ Caliper Tool has detected and classiÞed the edge pairs, their details are overlaid using Show Caliper Measurements.vi (available on the accompanying CD-ROM). This VI uses both the caliper report and the edge coordinates outputs from IMAQ Caliper Tool. The format of the edge coordinates array is different to that output by IMAQ Edge Tool — it does not represent simply a list of the detected edges, but each pair of array elements are the edge pairs detected. Considering the ROI intensity plot example in Figure 7.55, the coordinates contained
202 Image Acquisition Processing with LabVIEW FIGURE 7.56 Using the caliper. TABLE 7.5 “Caliper Parameters” Cluster Elements Element Polarity Separation Separation deviation Description This controls what are to be considered the leading and trailing edges during the search. There are Þve possible polarity settings: None: All edges are considered as leading and trailing edges. Dark-Light: Leading=Dark, Trailing=Light Light-Dark: Leading=Light, Trailing=Dark Dark-Dark: Both Leading and Trailing=Dark Light-Light: Both Leading and Trailing=Light SpeciÞes the expected spatial difference between the edge pairs. Only edge pairs around this value (within the tolerance deÞned by the separation deviation) are considered. If separation is set to 0, all edge pairs detected are considered. DeÞnes the tolerance value for the separation between the edges. FIGURE 7.57 Using the caliper — wiring diagram.
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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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