Image Processing Toolbox

Linear Filtering

Filtering is a technique for modifying or enhancing an image. For example, you can filter an image to emphasize certain features or remove other features.

Filtering is a neighborhood operation, in which the value of any given pixel in the output image is determined by applying some algorithm to the values of the pixels in the neighborhood of the corresponding input pixel. A pixel's neighborhood is some set of pixels, defined by their locations relative to that pixel. (See Chapter 5, Neighborhood and Block Operations, for a general discussion of neighborhood operations.)

Linear filtering is filtering in which the value of an output pixel is a linear combination of the values of the pixels in the input pixel's neighborhood. For example, an algorithm that computes a weighted average of the neighborhood pixels is one type of linear filtering operation.

This section discusses linear filtering in MATLAB and the Image Processing Toolbox. It includes

• A description of how MATLAB performs linear filtering, using convolution
• A discussion about using predefined filter types

See Filter Design for information about how to design filters.

Linear Filtering and Filter Design

Convolution