Image Processing Toolbox User's Guide |

**Convolution**

Linear filtering of an image is accomplished through an operation called *convolution*. Convolution is a neighborhood operation in which each output pixel is the weighted sum of neighboring input pixels. The matrix of weights is called the *convolution kernel*, also known as the *filter.* A convolution kernel is a correlation kernel that has been rotated 180 degrees.

For example, suppose the image is

The following figure shows how to compute the (2,4) output pixel using these steps:

- Rotate the convolution kernel 180 degrees about its center element.
- Slide the center element of the convolution kernel so that it lies on top of the (2,4) element of
`A`

. - Multiply each weight in the rotated convolution kernel by the pixel of
`A`

underneath. - Sum the individual products from step 3.

Hence the (2,4) output pixel is

**Computing the (2,4) Output of Convolution
**

Linear Filtering | Correlation |

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