Image Processing Toolbox

Correlation

The operation called correlation is closely related to convolution. In correlation, the value of an output pixel is also computed as a weighted sum of neighboring pixels. The difference is that the matrix of weights, in this case called the correlation kernel, is not rotated during the computation. Figure 7-2 shows how to compute the (2,4) output pixel of the correlation of A, assuming h is correlation kernel instead of a convolution kernel, using these steps:

1. Slide the center element of the correlation kernel so that lies on top of the (2,4) element of A.
2. Multiply each weight in the correlation kernel by the pixel of A underneath.
3. Sum up the individual products from step 3.

The (2,4) output pixel from the correlation is

Figure 7-2: Computing the (2,4) Output of Correlation

Convolution

Filtering Using imfilter