Accelerating the pace of engineering and science

# Documentation Center

• Trial Software

# indwt2

Inverse nondecimated 2-D wavelet transform

## Syntax

C = indwt2(W,TYPE,N)
C = indwt2(W,TYPE)
C = indwt2(W,TYPE,N)
X = indwt2(W)
X = indwt2(W,'a',0)
X = indwt2(W,'ca',0)

## Description

indwt2 performs a multilevel nondecimated 2-D wavelet reconstruction starting from a multilevel nondecimated 2-D wavelet decomposition. You can also use indwt2 to extract coefficients from a multilevel nondecimated 2-D wavelet decomposition.

C = indwt2(W,TYPE,N) computes the reconstructed or the extracted components at level N of a nondecimated 2-D wavelet decomposition. N must be a positive integer less or equal to the level of the decomposition. The valid values for TYPE are:

• A group of 2 chars 'xy', one per direction, with 'x' and 'y' in the set {'a','d','l','h'} or in the corresponding uppercase set {'A','D','L','H'}), where 'A' (or 'L') stands for low-pass filter and 'D' (or 'H') stands for high-pass.

• The char 'd' (or 'h' or 'D' or 'H') specifies the sum of the components different from the low-pass one.

For extraction, the valid values for TYPE are the same as above prefixed by 'c' or 'C'.

C = indwt2(W,TYPE) is equivalent to C = indwt2(W,TYPE,N) with N equal to the level of the decomposition.

X = indwt2(W), X = indwt2(W,'a',0) or X = indwt2(W,'ca',0) reconstructs the matrix X based on the nondecimated 2-D wavelet decomposition structure W.

## Examples

% Decompose X at level 3 using db1.
W = ndwt2(X,3,'db1');

% Reconstruct approximations at levels 1 to 3.
A = cell(1,3);
for k=1:3, A{k} = indwt2(W,'aa',k); end

% Plot original image at the top and approximations
% at the bottom.
figure; colormap(pink(255))
subplot(2,3,2);image(X);
for k=1:3
subplot(2,3,k+3);image(A{k});
end

% Reconstruct detail at level 1.
D = indwt2(W,'d',1);

% Display reconstructed detail at level 1.
figure; colormap(pink(255));imagesc(abs(D))

% Compute reconstructed approximation and detail at level 1.
A1 = indwt2(W,'aa',1);
D1 = indwt2(W,'d',1);

% Check that X = A1 + D1.
E1 = X-A1-D1;
err1 = max(abs(E1(:)))

err1 =

2.6645e-013

% Compute reconstructed approximation and detail at level 2.
A2 = indwt2(W,'aa',2);
D2 = indwt2(W,'d',2);

% Check that X = A2 + D2.
E2 = X-A2-D2;
err2 = max(abs(E2(:)))

err2 =

2.5668e-013