Rockwell Automation 5370-CVIM2 Module - Manual (Page 307)

5 Chapter Chapter 7
Inspection Tools
7–69
In Figure 7.57, the X Edge kernel causes the gradient (edge) on the left side
of the inspected object to appear as a vertical line of light pixels, and the
right gradient (edge) to appear as a line of dark pixels. The pixels
surrounding the two gradients were converted to medium gray. (Compare the
results in this figure to the results of the
Sobel X kernel in Figure 7.52 on
page 7–63.)
Note that the Sign LUT was selected for the example. Since the X Edge
kernel creates a signed image, which contains pixel values between –128 and
+127, the
Sign LUT removes negative values from the image by adding 128
to each value, thereby placing all pixel values in the 0 to 255 range that the
inspection tools require to identify and evaluate features properly.
Note also that the Absolute , S.Threshold , or S.Clip LUT could be used,
since they also remove negative values from the image. The choice of LUT
depends on the specific requirements for the application.
The effects on the inspected object that the Absolute and S.Threshold
LUTs have when using the X Edge kernel would be similar to the Sobel X
examples in Figure 7.53 (page 7–64). The main difference is that the X Edge
kernel produces a wider gradient.
Y Edge Kernel –– The coefficients in the Y Edge kernel are arrayed as
follows:
1 1
1
0
2
0
2 1
1
0
1
4 2
0 0
–1 –2 –1 –4 –2
–1 –1 –2 –1 –1
Figure 7.58 (page 7–70) uses the inspected object shown in Figure 7.57 (page
7–68) to illustrate the effect of the
Y Edge kernel.
In Figure 7.58, the Y Edge kernel causes the gradient (edge) on the top side
of the inspected object to appear as a horizontal line of light pixels, and the
bottom gradient (edge) to appear as a line of dark pixels. The pixels
surrounding the two gradients were converted to medium gray.
Note that the Sign LUT was selected for the example. Since the Y Edge
kernel creates a signed image, which contains pixel values between –128 and
+127, the
Sign LUT removes negative values from the image by adding 128
to each value, thereby placing all pixel values in the 0 to 255 range that the
inspection tools require to identify and evaluate features properly.
Note also that the Absolute , S.Threshold , or S.Clip LUT could be used,
since they also remove negative values from the image. The choice of LUT
depends on the specific requirements for the application.