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IMAGE Processing with LabVIEW and IMAQ Vision
Figure 4.25. Filter Example: Gradient (#0)
Note that the center coefficient of this kernel is 0; if we make it equal to 1 (as
in Figure 4.26), the edge information is added to the original value. The original image remains and the edges in the specified direction are highlighted.
Figure 4.27 shows the similar effect in a horizontal direction (dark-bright
changes from bottom to top).
Gradient kernels like those in Figure 4.25 and Figure 4.27 are also known
as Prewitt filtersor Prewittkernels. Another group of gradient kernels, for
−1 0 1


example, F =  −2 0 2 , are called Sobel filters or Sobel kernels. A Sobel
−1 0 1
kernel gives the specified filter direction a stronger weight.
In general, the mathematic value gradient specifies the amount of change of
a value in a certain direction. The simplest filter kernels, used in two orthogonal directions, are