- Two classes of high-pass filters can be distinguished: gradient (or directional) filters
and Laplacian (or non-directional) filters.
- Gradient filters are directional filters and are used to enhance specific linear trends.
- Laplacian filters are non-directional filters because they enhance linear features
having almost any direction in an image.
- A filter usually consists of a 3x3 array (sometimes called kernel) of coefficients or
weighting factors.
- Each pixel value is multiplied by the corresponding coefficient in the filter. The 9
values are summed and the resulting value replaces the original value of the central
pixel. This operation is called convolution.