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BlockMean

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BLOCKMEAN - Fast mean of rectangular submatrices

The mean of V*W elements along the 1st and 2nd dimension is calculated. This is no running mean filter: The sizes of the 1st and 2nd dimension are reduced by the factors V and W.
I use this as cheap anti-aliasing of RGB images, therefore it is implemented for DOUBLE and UINT8 input.

Y = BlockMean(X, V, W)
Input:
X: UINT8 or DOUBLE array of any size.
V, W: 2 scalars as size of the window. Each element of the output is the
mean over V*W neighbouring elements of the input.
V and W are limited to 256 to limit memory usage.
Output:
Y: UINT8 or DOUBLE array, the 1st and 2nd dimensions are V and W times shorter:
[FIX(X / V) x FIX(Y / W) x (further dims...)]
If the size of the 1st or 2nd dimension is not a multiple of V and W, the
remaining elements at the end are skipped.

E.g. for 4x4 blocks of a 1024x768x3 double array, this MEX implementation is about 5 times faster than the corresponding Matlab method (Matlab 2009a, 1.5GHz Pentium-M, WinXP, MSVC 2008):
reshape(sum(sum(reshape(X, 4, 256, 4, 192, 3), 1), 3), 256, 192, 3).
Run the unit-test uTest_BlockMean to check validity and speed.

Tested with: LCC v2.4, v3.8, Open Watcom 1.8, BCC 5.5, MSVC 2008, Matlab 6.5, 7.7, 7.8, WinXP 32 bit
Compatibility assumed: Linux, MacOS, 64bit.

Pre-compiled Mex: http://www.n-simon.de/mex

I'd appreciate suggestions for improvements and bug reports sent through email - thanks.

Free download from Shareware Connection - BLOCKMEAN - Fast mean of rectangular submatrices

Publisher: Jan Simon | License: Shareware
Version: 1.0 | Size: 10 KB | Platform: Matlab, Scripts
Released Date: 10-01-2013 | Rating: 0 | Title: BlockMean

Author Url: http://www.mathworks.com
Program Info Url: http://www.mathworks.com
Download Url: http://www.mathworks.com/matlabcentral/fx_files/24812/3/BlockMean_05Nov2010.zip

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Shareware Connection periodically updates pricing and software information of 'BlockMean' from company source 'Jan Simon' , so some information may be slightly out-of-date. You should confirm all information before relying on it. Software piracy is theft,  Using 'BlockMean' crack, password, serial numbers, registration codes, key generators is illegal and prevent future development of BlockMean.

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