detcoef2

2-D detail coefficients

Syntax

y = detcoef2(o,c,s,n)

[h,v,d] = detcoef2('all',c,s,n)

y = detcoef2('compact',c,s,n)

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.

[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

Extract Detail Coefficients From Image

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');

load woman
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

o — Orientation

'h' | 'v' | 'd'

Orientation of detail coefficients, specified as:

• 'h' — Horizontal

• 'v' — Vertical

• 'd' — Diagonal

c — Wavelet decomposition vector

real-valued vector

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

s — Bookkeeping matrix

integer-valued matrix

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

n — Detail level

integer

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

y — Detail coefficients

vector | matrix

Detail coefficients, returned as a vector or matrix.

Data Types: double

h — Horizontal detail coefficients

matrix

Horizontal detail coefficients, returned as a matrix.

Data Types: double

v — Vertical detail coefficients

matrix

Vertical detail coefficients, returned as a matrix.

Data Types: double

d — Diagonal detail coefficients

matrix

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.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

The detcoef2 function supports GPU array input with these usage notes and limitations:

• detcoef2 supports only the 'sym' and 'per' extension modes. See dwtmode.

• detcoef2 supports only these syntaxes:

  • y = detcoef2(o,c,s,n)

  • [h,v,d] = detcoef2('all',c,s,n)

For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Version History

Introduced before R2006a