Why does Matlab duplicate the output image ?

Hello,

I tried to implement the thresholding technique in image processing to an image, it works but the image appears 3 times instead of one, Does anyone have an idea what went wrong?

code:

i=imread("jk.jpg");

[a,b]=size(i);

new=zeros(size(i));

n=input("Enter thresholding key");

for x=1:a

for y=1:b

if i(x,y)<=n

new(x,y)=0;

else

new(x,y)=255;

end

end

end

imshow(new);

Answer 1

[DGM]

There are a number of things going wrong here, none of which should cause an image to be displayed multiple times. ... at least not as far as I've noticed.

i=imread('peppers.png'); % this is likely uint8, RGB
[a,b]=size(i); % for any RGB image, b will be wrong
new=zeros(size(i)); % the class of this array is 'double'

% you're writing a script do do something programmatically
% so why force your script to stop and ask you repeatedly
% for a number that you could have just written as a parameter?
n=128;%input("Enter thresholding key");

% this entire loop is unnecessary
for x=1:a % x and y are backwards
    for y=1:b
        if i(x,y)<=n
            new(x,y)=0;
        else
            % you're assigning the output scale contrary to the
            % class of the preallocated array. The output image
            % will be improperly scaled for its class, though the
            % gross truncation won't be consequential in this case.
            new(x,y)=255; 
        end
    end
end
imshow(new);

[a b] % the image is 384x512

ans = 1×2

384 1536

If you request N outputs from size(), the Nth output argument isn't the size of the Nth dimension. It's the product of the sizes of the Nth dimension and all higher dimensions. Surprisingly, the fact that b is wrong doesn't result in an indexing error, though I don't know that it would be good practice to rely on tricks like that.

This whole thing can be simplified.

inpict = imread('peppers.png'); % read any image
threshold = 128; % threshold value as a simple parameter

mask = inpict > threshold; % this is a logical image
mask = im2uint8(mask); % now it's a uint8 image

imshow(mask);