- Gradient filters are directional filters and are use 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 3*3 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 of the central pixel. This operation is called convolution.