data/code/functions/downsampleMRI2d.m

% This function downsamples an MRI struct in memory by a given factor
function mri2 = downsampleMRI2d(mri,factors,mode)

if nargin<3
    mode='linear';
end

if length(factors)==1
    factors=repmat(factors,[1 2]);
end

if strcmp(mode,'nearest')  % smooth unless we're doing labels
    S=mri.vol;
else
    S=GaussFilt2d(mri.vol,0.4*factors);
end

[II,JJ]=ndgrid(.5+factors(1)/2:factors(1):size(S,1),.5+factors(2)/2:factors(2):size(S,2));
I=interpn(S,II,JJ,mode);

mri2=[];
mri2.vol=I;
mri2.volres=mri.volres.*[factors(2) factors(1) 1];
mri2.vox2ras0=mri.vox2ras0;
mri2.vox2ras0(1:3,1:3)=mri.vox2ras0(1:3,1:3).*repmat([factors(2) factors(1) 1],[3 1]);
mri2.vox2ras0(1:3,4)=mri2.vox2ras0(1:3,4)+mri.vox2ras0(1:3,1:3)*([factors(2); factors(1); 1]/2-0.5);