image processing, k nearest neighbor

Asked by Ahsen Feyza Dogan on 12 Jul 2019

Latest activity Commented on by KSSV on 12 Jul 2019

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Hi, I am trying to make image classification with knn but I stuck in how can I compare selected paint and neighbor pixel value. Thank you

clc;
clear all;
a=imread('coins.png');
b=im2bw(a);
imshow(b);
c=zeros(size(b));
[ptx,pty] = ginput(1);
newdata=[ptx, pty];
[nx,ny] = size(b);
[X,Y] = meshgrid(1:nx,1:ny) ; 
ed=sqrt(((newdata(1)-X).^2)+((newdata(2)-Y).^2));   
dist=ed(:);
neighbor = mink(dist,400);
num=0;
threshold=201;
ind = ismember(dist, neighbor);
% Extract the elements of a at those indexes.
%num=0;
label=0;
% %find index of neighbor in euc then obtain label
indexes = find(dist);
for i=1:neighbor
  
    if b(indexes(i))==1
        num=num+1;
        if num>=threshold
            
            label=1;
        else
            label=3;
        end
    end
 
end

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Answer by KSSV on 12 Jul 2019

This is how you can use knnsearch.

a=imread('coins.png');
b=im2bw(a);
c=zeros(size(b));
[ptx,pty] = ginput(1);
newdata=[ptx, pty];
[nx,ny] = size(b);
[X,Y] = meshgrid(1:nx,1:ny) ;
ed=sqrt(((newdata(1)-X).^2)+((newdata(2)-Y).^2));
n = 10 ; % number of neighbor points needed
idx = knnsearch([X(:),Y(:)],[ptx pty],'k',n) ; 
imshow(b);
hold on
plot(X(idx),Y(idx),'*r')
plot(ptx,pty,'*g')

2 Comments

KSSV on 12 Jul 2019

Ahsen Feyza Dogan commented: Thank you. How can I compare pixel value of this neighbors and picked data?

KSSV on 12 Jul 2019

knnsearch gives you the indices of the neighboring points to a given point. If idx are the indicesm then the pixels for the given points are I(idx).

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