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

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vishnu
vishnu 2012-1-5
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
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
Image Analyst 2012-1-5
I have no idea what coefficients you're talking about, despite this poorly commented code.

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