calculating the neighbour values

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kash
kash 2012-9-30
i have a matrix
A=[1 2 3
4 5 6
7 8 9 ]
please tell how to calculate the neighbour values of centre pixel

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2012-9-30
编辑：Andrei Bobrov 2012-10-1
A = [ 542 605 341 615 928
471 550 839 1185 315
945 798 809 421 625
982 876 201 723 863
231 932 147 277 1100]; %initial matrix
out1 = cell(numel(A),1);
q = false(size(A));
for ii = 1:numel(A)
w = q;
w(ii) = true;
w1 = imdilate(w,[1 1 1;1 0 1;1 1 1]);
out1{ii} = A(w1);
end
% other variant
B = padarray(A,[1 1],nan);
s = size(B);
addm = bsxfun(@plus,(0:2)',(0:2)*s(1));
ad = addm(:)';
C = reshape(1:prod(s),s);
C = C(1:end-2,1:end-2);
out2 = B(bsxfun(@plus,C(:),ad([1:4,6:9])));
% the centre pixel values is 809 and has index:
i1 = 13;
out1{i1}
ans =
550
798
876
839
201
1185
421
723
>> out2(i1,:)
ans =
550 798 876 839 201 1185 421 723
>>
  2 个评论
kash
kash 2012-10-1
A = randi(1234,5,5)
A =
542 605 341 615 928
471 550 839 1185 315
945 798 809 421 625
982 876 201 723 863
231 932 147 277 1100
In this the centre pixel values is 809,i need 8 neighbours aroubd it
550 839 1185 798 876 201 723 421

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更多回答（2 个）

Matt J
Matt J 2012-9-30
>> A(5)=[]
A =
1 4 7 2 8 3 6 9
  2 个评论
kash
kash 2012-9-30
MAtt assume it may be large matrix 256x256,i just posted that for example
Jan
Jan 2012-10-1
@kash: Please do not post a specific problem, when you want to solve a more general problem. This wastes the time of the ones, who want to help you.

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Matt J
Matt J 2012-9-30
If you have the center pixel as a subscript index (m,n), then do
B=A((-1:1)+m,(-1:1)+n);
B(5)=[];
If you have the center pixel as a linear index, you can do as in the following example:
A =
0.3380 0.3042 0.2004 0.3071
0.8604 0.1598 0.5558 0.2813
0.7002 0.6425 0.9985 0.5409
0.2507 0.7799 0.2056 0.7081
jumps=bsxfun(@plus,[0;1;2],[0 1 2]*size(A,2));
jumps=jumps-jumps(5);
jumps(5)=[];
Now, Suppose I want the neighbourhood of A(6)=0.1598. Then I would do
>> A(jumps+6)
ans =
0.3380 0.8604 0.7002 0.3042 0.6425 0.2004 0.5558 0.9985
  5 个评论
显示 3更早的评论
Image Analyst
Image Analyst 2012-9-30
Let me repeat Matt's statement, which you just seemed to ignore: "You haven't said how you want to handle pixels on the edge of the matrix." In fact, if you just think about this, write down numbers near the edge of your matrix so you can visualize it, I think you'd be able to figure it out yourself.
Matt J
Matt J 2012-9-30
"i need only 8 neighbours"
You mean you think the error is triggered by a non-boundary pixel? Show us the larger code that you're using. Also, use DBSTOP to see the center pixel coordinates that are generating the error.

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