Spatial Domain Filtering
Image activities were included to allow the reader to perform filtering using some of the spatial domain filters built into the program. The operations fall into the image enhancement category of image processing, and are also important as preliminary steps, or preprocessing operations, in image analysis. The maximum and minimum filters are easy to understand: each pixel in the image is replaced by the largest, or smallest, value in its neighborhood. Four commonly available rank filters are the median, maximum, minimum and range filters. Larger filters change the image more, because pixels from further away from the pixel of interest are included in the calculations. Hybrid filters may include both rank and convolution steps, or may involve an additional image processing operation. Adaptive filters perform a different operation depending on the image content in the region in which they are being applied.