# detcoef2

2-D detail coefficients

## Description

y = detcoef2(o,c,s,n) extracts from the wavelet decomposition structure [c,s] the detail coefficients of orientation o at level n. For more information on c and s, see wavedec2.

example

[h,v,d] = detcoef2('all',c,s,n) returns the horizontal h, vertical v, and diagonal d detail coefficients at level n.

detcoef2('a',c,s,n) is equivalent to detcoef2('all',c,s,n).

y = detcoef2('compact',c,s,n) returns all the detail coefficients stored row-wise.

detcoef2('c',c,s,n) is equivalent to detcoef2('compact',c,s,n).

If [H,V,D] = detcoef2('all',c,s,N) and Y = detcoef2('compact',c,s,N), then Y = [H(:)' V(:)' D(:)'].

## Examples

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This example shows how to extract detail coefficients from a discrete wavelet analysis of an image. This example uses zero-padding.

Set the extension mode to zero-padding. Load and display an image.

origmode = dwtmode('status','nodisplay');
dwtmode('zpd','nodisplay');

imagesc(X)
colormap(gray)

Obtain the wavelet decomposition of the image down to level two using the Haar wavelet.

[c,s] = wavedec2(X,2,'haar');
size(X)
ans = 1×2

256   256

size(c)
ans = 1×2

1       65536

s
s = 4×2

64    64
64    64
128   128
256   256

Extract the detail coefficients at level 2 in each orientation from the wavelet decomposition structure [c,s]. Display the diagonal detail coefficients.

[chd2,cvd2,cdd2] = detcoef2('all',c,s,2);
size(cdd2)
ans = 1×2

64    64

imagesc(cdd2)
colormap(gray)

Extract the detail coefficients at level 1 in each orientation. Display the vertical detail coefficients.

[chd1,cvd1,cdd1] = detcoef2('all',c,s,1);
size(cvd1)
ans = 1×2

128   128

imagesc(cvd1)
colormap(gray)

Restore the original extension mode.

dwtmode(origmode,'nodisplay')

## Input Arguments

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Orientation of detail coefficients, specified as:

• 'h' — Horizontal

• 'v' — Vertical

• 'd' — Diagonal

Wavelet decomposition vector, specified as a real-valued vector. The vector c contains the approximation and detail coefficients organized by level. The bookkeeping matrix s is used to parse c. See wavedec2.

Data Types: double

Bookkeeping matrix, specified as an integer-valued matrix. The matrix s contains the dimensions of the wavelet coefficients by level and is used to parse the wavelet decomposition vector c. See wavedec2.

Data Types: double

Detail level to extract from the wavelet decomposition, specified as an integer. The integer n must be in the interval [1,size(s,1)-2].

## Output Arguments

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Detail coefficients, returned as a vector or matrix.

Data Types: double

Horizontal detail coefficients, returned as a matrix.

Data Types: double

Vertical detail coefficients, returned as a matrix.

Data Types: double

Diagonal detail coefficients, returned as a matrix.

Data Types: double

## Tips

• If c and s are obtained from an indexed image analysis or a truecolor image analysis, y is an m-by-n matrix or an m-by-n-by-3 array, respectively.

For more information on image formats, see the image and imfinfo reference pages.