A is less than a threshold

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Rocky
Rocky 2020-4-15
评论： Rocky 2020-4-16
m=256;
e=0.5;
for x=1:m
for y=1:m
if A(x,y)<0.5
s_dark(x,y)=A(x,y)^e;
end
end
end
Hello everyone.I have some problem in this code.The values less than 0.5 shold be stored in a variable s_dark.But i didn't get it.It store values less than 0.5 and also greater than 0.5.I've attached the s_dark variable below.please see through it.your help is really appreciated.

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Mehmed Saad
Mehmed Saad 2020-4-15
编辑：Mehmed Saad 2020-4-15
Because in your code
s_dark(x,y)=A(x,y)^e;
suppose A(x,y) = 0.47;
where e = 0.5;
0.47^0.5
ans =
0.6856
That is why you are getting values greater than 0.5
i think what you are trying to do is
m=256;
e=0.5;
A = A.^e;
for x=1:m
for y=1:m
if A(x,y)<0.5
s_dark(x,y)=A(x,y);
end
end
end
i am assuming that s_dark is initialized in the code earlier
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Rocky
Rocky 2020-4-16
Thank you for providing the link I will definitely go through it @stephen codeldick
Rocky
Rocky 2020-4-16
@Image Analyst..In my above code I simply comparing the A matrix with a threshold..if it is less than that threshold the values are stored in dark variable.And I raising e to the power of dark one..This is what I am doing.while using for loop instead of 0:255 I'm taking 1:256..I think I have clarified your question.If I'm wrong with my assumption you can point out my mistakes..

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更多回答（1 个）

Image Analyst
Image Analyst 2020-4-15
Not exactly sure what you want where A > 0.5, a value of 0 or of the original A? So here are both options:
% Initialization steps.
m = 256;
A = 0.7 * rand(m, m)
e = 0.5;
% OPTION 1
% s_dark equals A except where A is less than 0.5 where
% it will replace values of A less than 0.5 with
% the value raised to the e power
s_dark = A; % Initialize;
map = A < 0.5; % Logical matrix of where A is less than 0.5.
s_dark(map) = A(map) .^ e;
% OPTION 2
% s_dark equals 0 except where A is less than 0.5 where
% it will be the values of A raised to the e power
s_dark = zeros(size(A)); % Initialize;
map = A < 0.5; % Logical matrix of where A is less than 0.5.
s_dark(map) = A(map) .^ e;

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