Vectorize for loop: corr2(A(:,:,i),B(:,:,i))
显示 更早的评论
Hi, I am trying to accelerate a function and am unable to perform this myself, so I am hoping for your help.
I have a set of 10.000 small images (64x64), and I need to calculate the correlation coefficient for each of these images. This is the code:
clear all
clc
close all
A=rand(64,64,10000);
B=rand(64,64,10000);
corr_result=zeros(1,1,size(A,3));
tic
for i=1:size(A,3)
corr_result(i)=corr2(A(:,:,i),B(:,:,i));
end
toc
I found this, it results in a 64x64x1 matrix, but I need a 1x1x10000 matrix.... Thanks for your input!!
5 个评论
Deepak Gupta
2020-12-3
编辑：Deepak Gupta
2020-12-3
I ran this code and got a matrix of size 64x64x10000 matrix. Don't know what's the problem.
Ameer Hamza
2020-12-3
but I need a 1x1x10000 matrix
Can you explain how? Shouldn't it be 64x64x10000?
William Thielicke
2020-12-3
编辑：William Thielicke
2020-12-3
Ameer Hamza
2020-12-3
I think this is already as efficient as it can get in MATLAB. After JIT optimizations, for-loops are not as slow as one might think.
William Thielicke
2020-12-3
采纳的回答
Bruno Luong
2020-12-3
编辑：Bruno Luong
2020-12-3
If you have R2020b, you mght try to vectorize with pagemtimes function (or use mtimesx from File exchange)
meanA = mean(A,[1 2]);
meanB = mean(B,[1 2]);
Ac = A-meanA;
Bc = B-meanB;
Ac = reshape(Ac,[],1,size(A,3));
Bc = reshape(Bc,[],1,size(B,3));
% psfun = @(a,b) sum(a.*b,1);
psfun = @(a,b) pagemtimes(a,'transpose',b,'none');
C = psfun(Ac,Bc)./sqrt(psfun(Ac,Ac).*psfun(Bc,Bc))
3 个评论
William Thielicke
2020-12-3
Thank you, your solution is 3 - 4 times faster, and gives the identical result:
William Thielicke
2020-12-3
... but beware when you hit the limit of your RAM.... then it suddenly becomes 7 times slower. Is there a way to predict which method is faster BEFORE doing the calculation? I guess it has something to do with the memory used by the variables and the available RAM.
Bruno Luong
2020-12-3
Divide the calculation into a chunks that do not exeed your PC ram, eg 8e4 images.
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Image Arithmetic 的更多信息
产品
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
