Brief Description
The hit-and-miss transform is a general binary morphological operation that can be used to look for particular patterns of foreground and background pixels in an image. It is actually the basic operation of binary morphology since almost all the other binary morphological operators can be derived from it. As with other binary morphological operators it takes as input a binary image and a structuring element, and produces another binary image as output.
How It Works
The structuring element used in the hit-and-miss is a slight extension to the type that has been introduced for erosion and dilation, in that it can contain both foreground and background pixels, rather than just foreground pixels, i.e. both ones and zeros. Note that the simpler type of structuring element used with erosion and dilation is often depicted containing both ones and zeros as well, but in that case the zeros really stand for `don't care's', and are just used to fill out the structuring element to a convenient shaped kernel, usually a square. In all our illustrations, these `don't care's' are shown as blanks in the kernel in order to avoid confusion. An example of the extended kind of structuring element is shown in Figure 1. As usual we denote foreground pixels using ones, and background pixels using zeros.
Figure 1 Example of the extended type of structuring element used in hit-and-miss operations. This particular element can be used to find corner points, as explained below.
The hit-and-miss operation is performed in much the same way as other morphological operators, by translating the origin of the structuring element to all points in the image, and then comparing the structuring element with the underlying image pixels. If the foreground and background pixels in the structuring element exactly match foreground and background pixels in the image, then the pixel underneath the origin of the structuring element is set to the foreground color. If it doesn't match, then that pixel is set to the background color.
For instance, the structuring element shown in Figure 1 can be used to find right angle convex corner points in images. Notice that the pixels in the element form the shape of a bottom-left convex corner. We assume that the origin of the element is at the center of the 3×3 element. In order to find all the corners in a binary image we need to run the hit-and-miss transform four times with four different elements representing the four kinds of right angle corners found in binary images. Figure 2 shows the four different elements used in this operation.
Brief Description
The hit-and-miss transform is a general binary morphological operation that can be used to look for particular patterns of foreground and background pixels in an image. It is actually the basic operation of binary morphology since almost all the other binary morphological operators can be derived from it. As with other binary morphological operators it takes as input a binary image and a structuring element, and produces another binary image as output.
How It Works
The structuring element used in the hit-and-miss is a slight extension to the type that has been introduced for erosion and dilation, in that it can contain both foreground and background pixels, rather than just foreground pixels, i.e. both ones and zeros. Note that the simpler type of structuring element used with erosion and dilation is often depicted containing both ones and zeros as well, but in that case the zeros really stand for `don't care's', and are just used to fill out the structuring element to a convenient shaped kernel, usually a square. In all our illustrations, these `don't care's' are shown as blanks in the kernel in order to avoid confusion. An example of the extended kind of structuring element is shown in Figure 1. As usual we denote foreground pixels using ones, and background pixels using zeros.
Figure 1 Example of the extended type of structuring element used in hit-and-miss operations. This particular element can be used to find corner points, as explained below.
The hit-and-miss operation is performed in much the same way as other morphological operators, by translating the origin of the structuring element to all points in the image, and then comparing the structuring element with the underlying image pixels. If the foreground and background pixels in the structuring element exactly match foreground and background pixels in the image, then the pixel underneath the origin of the structuring element is set to the foreground color. If it doesn't match, then that pixel is set to the background color.
For instance, the structuring element shown in Figure 1 can be used to find right angle convex corner points in images. Notice that the pixels in the element form the shape of a bottom-left convex corner. We assume that the origin of the element is at the center of the 3×3 element. In order to find all the corners in a binary image we need to run the hit-and-miss transform four times with four different elements representing the four kinds of right angle corners found in binary images. Figure 2 shows the four different elements used in this operation.
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