Rockwell Automation 5370-CVIM2 Module - Manual (Page 301)

5 Chapter Chapter 7
Inspection Tools
7–63
Figure 7.52 illustrates the effect of the Sobel X kernel on a dark object on a
light background.
Figure 7.52 Example: Effect of Sobel X Kernel on Inspected Object
Image tool
Inspected
object
In Figure 7.52, the Sobel X kernel causes the gradient on the left side of the
inspected object to appear as a thin vertical line of light pixels, and the right
gradient 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 Sobel X
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.