# Has anyone implemented moravec corner detector in matlab??

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B.k Sumedha on 20 May 2015
Answered: Ignacio Rocco on 14 Nov 2019
This is what i have tried.But with very less accurate.
clear all
close all
clc
tic
originalmap=I;
w=5;
m=floor(size(I,1)/w);
n=floor(size(I,2)/w);
c=ceil(w/2)+(0:n-1)*w;
r=ceil(w/2)+(0:m-1)*w;
step=floor(w/2);
for y_unit=1:m
for x_unit=1:n
v1=0;v2=0;v3=0;v4=0;
for i=-step:step-1
v1=v1+(I(r(y_unit),c(x_unit)+i)-I(r(y_unit),c(x_unit)+i+1))^2;
v2=v2+(I(r(y_unit)+i,c(x_unit)+i)-I(r(y_unit)+i+1,c(x_unit)+i+1))^2;
v3=v3+(I(r(y_unit)+i,c(x_unit))-I(r(y_unit)+i+1,c(x_unit)))^2;
v4=v4+(I(r(y_unit)-i,c(x_unit)+i)-I(r(y_unit)-i-1,c(x_unit)+i+1))^2;
end
IV_cr(y_unit,x_unit)=min([v1,v2,v3,v4]);
end
end
exper_thr=20;
IV_cr(IV_cr<exper_thr)=NaN;
wf=9;
mf=floor(m/wf);
nf=floor(n/wf);
xc=[];
yc=[]; for y_unit=1:mf
for x_unit=1:nf
[C,I]=max(IV_cr((y_unit-1)*wf+1:y_unit*wf,(x_unit-1)*wf+1:x_unit*wf))
[C1,I1]=max(C);
IV_crch(y_unit,x_unit)=C1;
row=I(I1);
col=I1;
crch_row(y_unit,x_unit)=(y_unit-1)*wf+row;
crch_col(y_unit,x_unit)=(x_unit-1)*wf+col;
yc=[yc,r((y_unit-1)*wf+row)];xc=[xc,c((x_unit-1)*wf+col)];
IV_cr((y_unit-1)*wf+1:y_unit*wf,(x_unit-1)*wf+1:x_unit*wf)=NaN;
IV_cr((y_unit-1)*wf+row,(x_unit-1)*wf+col)=C1;
end
end
figure(1)
imshow(originalmap)
figure(2)
plot(xc,yc,'*')
view(0,-90)
toc;
t=toc;
disp(['amount of time',num2str(t),'sec'])
figure(3)
imshow(originalmap)
hold on
plot(xc,yc,'R*')
axis on
end

Thorsten on 20 May 2015
I just did if for you:
function C = moravec(I)
%MORAVEC Moravec corner detector
%
% C = MORAVEC(I)
%
% Thorsten.Hansen@psychol.uni-giessen.de 2015-05-20
if nargin == 0 % simple test
I = zeros(100);
I(40:60, 40:60) = 1;
C = moravec(I);
imshow(0.5*C+I, [])
if nargout == 0, clear C, end
return
end
D(:,:,1) = diff([I I(:,end)]')';
D(:,:,2) = diff([I(:,1) I]')';
D(:,:,3) = diff([I; I(end,:)]);
D(:,:,4) = diff([I(1,:); I]);
C = sum(D.^2, 3);
if nargout == 0, clear C, end
B.k Sumedha on 20 May 2015
ok fyn

Ignacio Rocco on 14 Nov 2019
Hi,
Thanks Thorsten for your code! However I think it's missing a few details. I slightly modified the implementation according to the original text by Moravec [1980], and I think now it's producing much better results.
Here's the updated code.
function C = moravec(I)
%MORAVEC Moravec corner detector
%
% C = MORAVEC(I)
%
% Thorsten.Hansen@psychol.uni-giessen.de 2015-05-20
% Ignacio.Rocco@inria.fr 2019-11-14
if nargin == 0 % simple test
I = zeros(100);
I(40:60, 40:60) = 1;
C = moravec(I);
imshow(0.5*C+I, [])
if nargout == 0, clear C, end
return
end
D(:,:,1) = conv2(conv2(single(I),[1 -1],'same').^2,ones(3),'same');
D(:,:,2) = conv2(conv2(single(I),[1;-1],'same').^2,ones(3),'same');
D(:,:,3) = conv2(conv2(single(I),[1 0;0 -1],'same').^2,ones(3),'same');
D(:,:,4) = conv2(conv2(single(I),[0 1;-1 0],'same').^2,ones(3),'same');
C = min(D.^2,[], 3);
if nargout == 0, clear C, end