Measuring the Sampling Density

Stage micrometers are available from a variety of sources, including the major microscope manufacturers and other suppliers (e.g., Opto-Line Associates; see suppliers appendix). The central feature of a stage micrometer that makes it appropriate for determining the sampling density is that it is marked with a periodic series of stripes at known distance intervals. Two such stage micrometers are shown in Figure 2.6.5.

The line spacing can be measured using digital image processing techniques. The general idea is to identify those places on the bars where there is a transition either from black to white or from white to black. Then, by taking the distance between the transition positions over several periods of the bar pattern, it is possible to determine the average distance in pixels between the bars. This can then be converted to Ax and Ar

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