# Filter Size

You should specify a filter size that closely matches the size of the edges in your input images. The size of an edge is the number of pixels wide that the edge is. Edges can be sharp, in which case the edge only spans one or two pixels, or edges can be dull, in which case they might span many pixels. The following figure illustrates examples of sharp and dull edges; the figure illustrates both types of edges at different magnifications.

When you specify a filter size that is close to the edge size, the Caliper tool produces stronger edge peaks in the filter image. If you specify a filter size that is too large or too small, the filter image will contain broad, low peaks. The following figure illustrates the effect of applying filters of different sizes to sharp and dull edges.

The figure illustrates that the more closely you match the filter size to the size of the edges of interest within the image, the sharper the desired peaks in the filtered image and the fewer spurious peaks there will be.