Design for Embedded Image Processing on FPGAs, 2nd Edition

9Local Filters

Local filters extend point operations by having the output be some function of the pixel values within a local neighbourhood or window:

(9.1)

where is the window or local neighbourhood centred on , as illustrated in Figure 9.1. The window can be of any shape or size, but is usually square, pixels in size, with odd, so that the window centre is well defined. As the window is scanned through the input image, each possible position generates an output pixel according to Eq. (9.1). The filter function, , determines the type of filter. Since the output depends not only on the input pixel but also its local context, filters can be used for noise removal or reduction, edge detection, edge enhancement, line detection, and feature detection.

9.1 Window Caching

The software approach to filtering has both the input and output images stored in frame buffers. For each output pixel, ...