how to count number of iterations.?

 I = imread('Coins.jpg');
Id = im2double(I); % I is a uint8 grayscale image
T = 0.5*(min(Id(:)) + max(Id(:)));
deltaT = 0.01; % convergence criterion
done = false;

 while done
g = Id >= T;
Tnext = 0.5*(mean(Id(g)) + mean(Id(g)));
done = abs(T - Tnext) < deltaT;
T = Tnext;
end

i want to count number of iteration for this program.! as well i want to store value of T at each iteration.!

[Nimisha]

 I = imread('Coins.jpg');
Id = im2double(I); % I is a uint8 grayscale image
done = false;
count = 0
T = zeros(1,100); % Try to presize to something big enough to hold all iterations if you can estimate it
while done
   g = Id >= T;
   Tnext = 0.5*(mean(Id(g)) + mean(Id(g)));
   count = count + 1;
   T(count) = Tnext
end

Why we changed T.? Cant we do with previous T.?

And above is giving results as 0

[Adam]

I edited my answer below. I didn't notice the initialisation of T higher up and the >= test against it in the while loop.

Answer 1

[Adam]

count = 0
newT = zeros(1,100); % Try to presize to something big enough to hold all iterations if you can estimate it

while done
   g = Id >= T;
   Tnext = 0.5*(mean(Id(g)) + mean(Id(g)));
   count = count + 1;
   newT(count) = Tnext
   done = abs(T - Tnext) < deltaT;
end

Presize newT if you can come up with a sensible bounded estimate, otherwise the warning you get is likely irrelevant anyway. Your code will be a little slower, but unlikely to matter in this case.

[Nimisha]

 I = imread('Coins.jpg');
Id = im2double(I); % I is a uint8 grayscale image
T = 0.5*(min(Id(:)) + max(Id(:)));
deltaT = 0.01; % convergence criterion
done = false;
count = 0
newT = zeros(1,100); % Try to presize to something big enough to hold all iterations if you can estimate it
while done
   g = Id >= T;
   Tnext = 0.5*(mean(Id(g)) + mean(Id(g)));
   count = count + 1;
   newT(count) = Tnext
end

This gives 0 count and 0 value of newT at each point.

[Adam]

You initialise

done = false;

and then do

while done
...
end

This means your loop will not execute at all.

I thought the name of the loop variable was confusing when I glanced at it, but i didn't look at that part of the logic. To keep the variable name sensible what you want is

while ~done
...
end

[Image Analyst]

Why did you set done=false , so that you never enter the loop? And, even if you did get into the loop, you never update done so how would it know when to exit the loop? Please learn how to use the debugger. If you knew how, you'd step through the code line by line and you would have seen that you never enter the loop. Debugging it yourself is SO much faster than debugging via back and forth messages in a discussion forum. Even after you fix those, there are other errors I can see that I haven't told you about but which you'll discover, and probably realize how to fix once you see them, when you step through the program.

[Adam]

Note, I just edited my original answer to add in the updating of done in the loop that I accidentally missed out first time.

[Nimisha]

Ya, This ~ sign works. Thank You very Much :)

[Adam]

No problem :)

Would have been a bit quicker if I absorbed your whole original post first time, but I was trying to just scan it for the parts relevant to the question which turned out to be a mistake!