Hi... a image is there .. how to select some particular amount non zero coefficients ?

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vishnu 2012-1-5

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https://ww2.mathworks.cn/matlabcentral/answers/25349-hi-a-image-is-there-how-to-select-some-particular-amount-non-zero-coefficients

关闭： MATLAB Answer Bot 2021-8-20

for examble 2568256 ....i want to take (256*256)/4 coefficients .. is thresholding is the method for this .. if thresholding is the method to do this whether we have to set manually value to select upper thershold?

   if pixelvalue >150
{
select 
}
else{}
this concept will work it out?

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vishnu 2012-1-5

function [B,T] = MinimaxAT(I)

% I: input image

% B: thresholded image

% T: Threshold surface

% implements a line search

Iterations = 1000; % increase if it is inadequate

epsilon=1e-7; % for termination condition, decrease if it is inadequate

pow=1; % although 1 is a pretty good value,

% you may need to play with this parameter, pow takes POSITIVE real values

I = double(I);

% linearly map I to the range [0, 1]

I(:) = (I-min(I(:)))/(max(abs(I(:)))-min(I(:)));

% display I

figure(1),imagesc(I),colormap(gray);axis image; drawnow;

[h,w] = size(I);

rowC = 1:h; rowN = [1 1:h-1]; rowS = [2:h h];

colC = 1:w; colE = [1 1:w-1]; colW = [2:w w];

Ix = (I(rowC,colW) - I(rowC,colE))/2; Ix(:,1) = 0; Ix(:,end) = 0;

Iy = (I(rowS,colC) - I(rowN,colC))/2; Iy(1,:) = 0; Iy(end,:) = 0;

% [Ix,Iy] = gradient(I);

g = (Ix.^2+Iy.^2).^(pow/2);

g(:) = g/max(g(:));

% initialize threhold surface

T=zeros(h,w);

Tx = T;

Ty = T;

delT=T;

delTx=T;

delTy=T;

figure(2),set(gcf,'doublebuffer','on');

old_alpha=10;

for n=1:Iterations,

% compute alpha

Tx(:) = (T(rowC,colW) - T(rowC,colE))/2; Tx(:,1) = 0; Tx(:,end) = 0;

Ty(:) = (T(rowS,colC) - T(rowN,colC))/2; Ty(1,:) = 0; Ty(end,:) = 0;

% [Tx,Ty] = gradient(T);

en1 = 0.5*sum(sum(g.*(T-I).^2));

en2 = 0.5*sum(sum(Tx.^2+Ty.^2));

alpha = en2/sqrt(en1^2+en2^2);

% line search

delT(:) = sqrt(1-alpha^2)*g.*(I-T) + alpha*(T(rowC,colW)+T(rowC,colE)+T(rowN,colC)+T(rowS,colC)-4*T);

delTx(:) = (delT(rowC,colW) - delT(rowC,colE))/2; delTx(:,1) = 0; delTx(:,end) = 0;

delTy(:) = (delT(rowS,colC) - delT(rowN,colC))/2; delTy(1,:) = 0; delTy(end,:) = 0;

% [delTx,delTy] = gradient(delT);

e2 = sqrt(1-alpha^2)*sum(sum(g.*(I-T).*delT)) - alpha*sum(sum(Tx.*delTx + Ty.*delTy));

e3 = sqrt(1-alpha^2)*sum(sum(g.*delT.*delT)) + alpha*sum(sum(delTx.*delTx + delTy.*delTy));

% delt should at least be 0.25

% minimize a quadratic expression: e1 - delt*e2 + 0.5*delt*delt*e3, see

% the journal paper

delt = max(0.25,e2/e3);

T(:) = T+delt*delT;

% show

figure(2),imagesc(I>T),colormap(gray);axis image;

title(['Iteration: ' num2str(n) ' alpha: ' num2str(alpha)]);

drawnow;

if abs(old_alpha-alpha)<=epsilon,

break;

end

old_alpha=alpha;

end

B = I>T;

% figure(3),imagesc(T),colormap(gray);axis image;

how can i use this code .. error coming

Image Analyst 2012-1-5

I have no idea what coefficients you're talking about, despite this poorly commented code.

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Hi... a image is there .. how to select some particular amount non zero coefficients ?

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Hi... a image is there .. how to select some particular amount non zero coefficients ?

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