# Finding value of a matrix

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FIR el 19 de Dic. de 2012
I have a 3x3 matrix, for example:
d=rand(3,3)
Now i want to implement the equation
V=1/2(d(q4,q5)+d(q5,q6))
where q5 is the centre pixel
q4,46 are neighbouring pixels
for example
d= q1 q2 q3
q4 q5 q6
q7 q8 q9
please assist
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Walter Roberson el 19 de Dic. de 2012
q4 and q5 and so on are values of those pixels?

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### Respuesta aceptada

Walter Roberson el 19 de Dic. de 2012
Hard to tell. You might be asking for
oldMatrix = double(ImageMatrix);
NewMatrix = ( oldMatrix(:,1:end-1) + oldMatrix(:,2:end) ) ./ 2;
But perhaps your "d" matrix is trying to talk about weighting the pixel values ? If so then let w1 be the weight for what you showed as d(q4,q5), and let w2 be the weight for what you showe as d(q5,q6), and then
NewMatrix = ( w1 .* oldMatrix(:,1:end-1) + w2 .* oldMatrix(:,2:end) ) ./ 2;
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FIR el 19 de Dic. de 2012
Editada: Walter Roberson el 19 de Dic. de 2012
Thanks walter
another thing i tought of doing it in a loop because ihave to replace some values so i tried for 7x7 from link
in the code for 7x7 matrix
for i=2:6
for j=2:6
K= A(i-1:i+1,j-1:j+1);
B(i,j)=median(K);
end
end
i get error
Subscripted assignment dimension mismatch.
Walter Roberson el 19 de Dic. de 2012
B(i,j)=median(K(:));

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### Más respuestas (2)

Muruganandham Subramanian el 19 de Dic. de 2012
Editada: Muruganandham Subramanian el 19 de Dic. de 2012
d=ones(3);
V=1/2*(d(d(2,2),d(2,2))+d(d(2,2),d(2,3)))
but, If you're using rand(), d(2,2),etc.. can't be accessible, if not using ceil() or floor()..Is this you want?
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Walter Roberson el 19 de Dic. de 2012
The confusion is between pixel locations and pixel values. You wrote the question with d(q4,q5) which based on the way you wrote the question is trying to access the matrix d() at row index which is the value of the pixel you labeled q4, and column index which is the value of the pixel you labeled q5.
Muruganandham Subramanian el 19 de Dic. de 2012
@FIR, I din't worked on images, anyway, by using imread() read your image and do the calculation

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Image Analyst el 19 de Dic. de 2012
By chance do you mean just convolution with a [1 2 1]/4 kernel, where you take the average of the left pair of pixels and the right pair of pixels? If so, you'd need to extract each color plane first and then use conv2() to get the output image one color plane at a time.
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