smooth2

Smooths the data in a 2D matrix with a user-defined resolution.

Description

SMOOTH2.M: Smooths matrix data.

MATRIXOUT=SMOOTH2(MATRIXIN,Nr,Nc) smooths the data in MATRIXIN using a running mean over 2*N+1 successive points, N points on each side of the current point. At the ends of the series skewed or one-sided means are used.

Inputs: matrixIn - original matrix
         Nr - number of points used to smooth rows
         Nc - number of points to smooth columns
Outputs: matrixOut - smoothed version of original matrix

Remark: By default, if Nc is omitted, Nc = Nr.

• Acknowledgements: This submission has inspired the following:; smoothc.mat, smooth2a
• MATLAB release: MATLAB 7 (R14)

[Tim Carlton]

This function does not work properly

[Phil Archer]

it works for me

[Mark Stoelinga]

Didn't work. Produced discontinuites.

[j bowling]

This works great

[C Manoj]

The output matrix has values much smaller that expected. Normalization ?

[Paul Griffin]

Does exactly what it says on the package.

[j bowling]

Output matrix has value smaller than expected? Needs some improvement

[Greg Reeves]

I took out the for loops and just used array algebra to do essentially the same thing. Improved speed ~10 fold. I didn't bother checking whether edge behavior is the same. My edge behavior is similar to the default behavior in Matlab's builtin smooth function.

%Initial error statements and definitions
if nargin<2, error('Not enough input arguments!'), end

N(1) = Nr;
if nargin<3
    N(2) = N(1);
else
    N(2) = Nc;
end

if length(N(1))~=1, error('Nr must be a scalar!'), end
if length(N(2))~=1, error('Nc must be a scalar!'), end

[row,col] = size(matrixIn);
eL = spdiags(ones(row,2*N(1)+1),(-N(1):N(1)),row,row);
eL = eL./(repmat(sum(eL,1),row,1));
eR = spdiags(ones(col,2*N(2)+1),(-N(2):N(2)),col,col);
eR = eR./(repmat(sum(eR,2),1,col));

matrixOut = eL*matrixIn*eR;

[Joan Pau]

Wrong results (e.g., a matrix like [ 1 8 1; 1 1 1; 1 1 1] gives [2.7500 1.0000 2.1667; 2.1667 1.0000 1.7778; 2.1667 1.0000 1.7778]) Don't think this was the result intended

[Nathan]

Greg Reeves' version indeed runs much faster, but gave me strange results in tests:
A =
1 2 3
4 5 6
7 8 9
smooth2(A,1) =
1.8 3.6 2.6
4.9 8.9 6.2
4.3 7.6 5.1

I switched rows and columns on the eL and eR matrices and was able to obtain results consistent with the documentation of Kelly Hilands' original code (at least for this test):
smooth2(A,1) =
3 3.5 4
4.5 5 5.5
6 6.5 7

Here is the corrected code (two lines are changed from Greg Reeves' code above)

%Initial error statements and definitions
if nargin<2, error('Not enough input arguments!'), end

N(1) = Nr;
if nargin<3
    N(2) = N(1);
else
    N(2) = Nc;
end

if length(N(1))~=1, error('Nr must be a scalar!'), end
if length(N(2))~=1, error('Nc must be a scalar!'), end

[row,col] = size(matrixIn);
eL = spdiags(ones(row,2*N(1)+1),(-N(1):N(1)),row,row);
eL = eL./(repmat(sum(eL,2),1,row)); % THIS LINE CHANGED FROM REEVES' CODE
eR = spdiags(ones(col,2*N(2)+1),(-N(2):N(2)),col,col);
eR = eR./(repmat(sum(eR,1),col,1)); % THIS LINE CHANGED FROM REEVES' CODE

matrixOut = eL*matrixIn*eR;

[Jakob]

I experienced vertical and horizontal jumps in the smoothing and spent quite a while searching for a better alternative when I came across the smooth2a file, found under acknowledgements on this page. If smooth2 fails for you I recommend checking smooth2a out.

[Moritz]