conv2 (MATLAB Function Reference)

Two-dimensional convolution

C = conv2(A,B)
C = conv2(hcol,hrow,A)
C = conv2(...,'shape')

Description

C = conv2(A,B)

computes the two-dimensional convolution of matrices A and B. If one of these matrices describes a two-dimensional FIR filter, the other matrix is filtered in two dimensions.

The size of C in each dimension is equal to the sum of the corresponding dimensions of the input matrices, minus one. That is, if the size of A is [ma,na] and the size of B is [mb,nb], then the size of C is [ma+mb-1,na+nb-1].

C = conv2(hcol,hrow,A)

convolves A separably with hcol in the column direction and hrow in the row direction. hcol and hrow should both be vectors.

C = conv2(...,'shape')

returns a subsection of the two-dimensional convolution, as specified by the shape parameter:


`full`	Returns the full two-dimensional convolution (default).
`same`	Returns the central part of the convolution of the same size as `A`.
`valid`	Returns only those parts of the convolution that are computed without the zero-padded edges. Using this option, `C` has size `[ma-mb+1,na-nb+1]` when `size(A)` > `size(B)`.

Examples

In image processing, the Sobel edge finding operation is a two-dimensional convolution of an input array with the special matrix

s = [1 2 1; 0 0 0; -1 -2 -1];

These commands extract the horizontal edges from a raised pedestal:

A = zeros(10);
A(3:7,3:7) = ones(5);
H = conv2(A,s);
mesh(H)

These commands display first the vertical edges of A, then both horizontal and vertical edges.

V = conv2(A,s');
mesh(V)
mesh(sqrt(H.^2+V.^2))