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function mMasked=MaskImageIn(m [,alphaIn])
% Accept an image matrix "m" and return "nMasked", holding the same image
% but with adjusted alpha values. MaskImageIn sets full transparency
% for pixels with value zero and sets full opacity for pixels with
% non-zero value.
%
% If the optional alphaIn argument is specified then MaskImageIn sets
% non-zero pixels to alphaIn opacity instad of to full opacity, 255.
%
% see also: SetImageAlpha, MaskImageOut, AlphaDemo.
% HISTORY
%
% mm/dd/yy
%
% 1/28/05 awi Wrote it.
if nargin<2
alphaIn=255;
end
dims=size(m);
numDims=length(dims);
if numDims > 3
error('The matrix argument must have no more than three dimensions');
if numDims==2
mMasked=repmat(m, [1, 1, 3]);
else
mMasekd=m;
end
sumPlanes=mMasked(:,:,1) + m(:,:,2) + m(:,:,3);
isNonZero=sumPlanes ~= 0;
nMasked(:,:,4)=isNonZero * alphaIn;
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