Creating custom filters

You can design your own filter by specifying the coefficients for a filter template. Custom filters perform spatial filtering on each pixel in an image using the gray-level values from either a square or a rectangular kernel surrounding each pixel.

Some common custom filters are

Weighted average
Directional
Center weighted

Click the Custom tab.
Enter your filter parameters in the matrix provided. For example, for a 3x3 filter you can use a1 a2 a3, a4 a5 a6, or a7 a8 a9, and so on. When you enter a range of a1 - a9, the filter is placed over the image so that the target pixel is covered by a5. The neighborhood pixels are then multiplied by the corresponding values in the filter and then summed. The pixel at a5 is replaced by this sum.
To read a kernel from a specific file, click Import. The number of entries in the first line of the file determines the number of columns in the kernel. All lines of data that follow have the same number of entries. If there are more, they are ignored. If there are less, then zeros are used to make up the difference. Data entries should be separated by spaces, tabs, or new lines.
To write a kernel to a file, click Export.
Click Normalize. The Normalize button divides all entries by the sum of the kernel entries. All other filtering algorithms normalize their respective kernels before performing the filtering operation. You can reset kernel entries to zero by clicking Reset.