Rockwell-automation 5370-CVIM2 Module Manual de usuario descargar pdf (Pagina 202)

100

101

Chapter

Chapter 6

Reference Tools

6–43

Scale To Selections

The Nearest Neighbor and Neighborhood Average “scale to” selections,

shown in Figure 6.37, have no effect when the X scale and Y scale selections

are both 1:1 –– they are applicable only when the X scale and/or Y scale

selections are other than 1:1.

Figure 6.37 Scale To Selections

Neighborhood Average –– This is the default selection. The template match

is based on the average gray value of the scaled neighborhood.

Nearest Neighbor –– The template match is based on picking the value of the

pixel that is in the upper–left corner of a block of pixels, such as “45” in

block “A” of Figure 6.35 (page 6–41). (In this case, “nearest neighbor”

would result in a single pixel with a gray scale value of 45.) Nearest neighbor

is a somewhat faster approximation for template matching purposes than

neighborhood average, but gives a less accurate approximation of the image.

Pixel Error Parameter Selections

The Ignore Pixel Errors  and Max. RMS Pixel Error parameters

determine, for the purposes of template matching, the extent to which the

gray values of the pixels in the search image are permitted to deviate from

the gray values of the pixels in the feature image and still achieve a

successful template match.

Ignore Pixel Errors  –– This parameter sets the value at (or below)

which pixel gray value mismatches (“pixel errors”) are ignored during the

search operation. The default setting is 10.

The term “error” refers to any difference between the gray value of a pixel in

the feature image and the gray value of the corresponding pixel in the search

image. For example, if the gray value of a particular feature image pixel were

20 and the corresponding search image pixel were 25, the error would be 5.

With the “Ignore” setting at the default value (10), the reference window

would ignore this error. If, however, the corresponding search image pixel

were 31, the error would be 11, and the reference window would recognize

that error.

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