# Filter (convolution)

A filter (also known as a kernel) is a small matrix used in convolution operations.

Convolution filters are commonly used in image processing to modify images or extract features.

The dimensions of a convolution filter are typically small, odd, and square. For example, convolution filters are typically $$3 \times 3$$ or $$5 \times 5$$ matrices. Odd dimensions are preferred to even dimensions.