Applying xcorr2 to match two subsequent images. Do I need normxcorr2, do I need to substract mean values?

7 次查看(过去 30 天)
Sorry for the title gore, but basically I am tracking the downward vertical flow of some bubbles. I have two images, the first at t=0, and then the bubbles have moved vertically to t=t. So basically I have the same image in both, but one is shifted by the vertical velocity of the bubbles.
I am applying a normxcorr2 to get my result, and it is working very well.
My code right now looks like this:
%first image
img1;
% second image
img2;
%cross correlation
ccr = ccr = normxcorr2(img1,img2);
%find the maximum
[ypeak,xpeak]=find(ccr==max(ccr(:)));
%convert to y coordinates
yoffset = ypeak-size(img2,1);
xoffset = xpeak-size(img2,2);
So visually inspecting my result, the match works very well.
My question is that from understanding what I am doing, if I was to apply just xcorr2, I would need to subtract the mean from each image (so that I have equal negative and positive values for the xcorr). Why don't I need to do this the normxcorr2.
I have tried applying just xcorr2 on img1 and img2, and also have tried applying xcorr2 on
img1 = img1 - mean(mean(img1))
I receive a similar, but different answer. Any ideas why?
Any sort of explanation here would be greatly appreciated.

回答(0 个)

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by