matlab - 简单的图像特征比较花费太多时间

Question

我有以下用于比较图像直方图特征的matlab代码；特征基本上是 3 维数组

for i=1:1:26
    for j=1:1:26
        s1=sum(image1(i,j,:));
        s2=sum(image2(i,j,:));
        if(s1>2 && s2>2)
            for k=1:1:31
                if image1(i,j,k)~=0 && image2(i,j,k)~=0  
                    d = d + ((image1(i,j,k) - image2(i,j,k))^2)/ (image1(i,j,k) + image2(i,j,k));
                end
            end
            count=count+1;
        end
    end
end

代码给出了令人满意的结果，但问题是它在我机器上的 matlab 中花费了很多时间(1 秒)，我真的需要优化它，欢迎任何其他方式的帮助或建议

Answer 1

这是一个vectorized方法-

%// Sum elements of image1 & image2 along the third dimension corresponding 
%// to s1 and s2 in the original loopy code
s1v = sum(image1,3);
s2v = sum(image2,3);

%// Pre-calculate all image1,image2 operations that lead to the calculation
%// of d in the original code
allvals = ((image1 - image2).^2)./(image1 + image2);

%// Calculate the first conditional values for the corresponding IF conditional
%// statement in original post - "if(s1>2 && s2>2)"
cond1 = s1v>2 & s2v>2

%// Sum all satisfying first conditional values for getting "count"
count = sum(cond1(:))

%// Calculate the second conditional values for the corresponding IF conditional
%// statement in original post - "if image1(i,j,k)~=0 && image2(i,j,k)~=0"
cond2 = image1~=0 & image2~=0;

%// Map both cond1 and cond2 onto allvals to select specific elements from
%// it and then sum those up for the final output, d
d = sum(cond1(:).'*reshape(cond2.*allvals,[],size(allvals,3)))

最后一行可以用 bsxfun 代替这样计算 -

d = sum(allvals(bsxfun(@and,cond1,cond2)))