cant seem to make the background fully black

Question

Pravindkumaran Baskaran 2022-9-30

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https://ww2.mathworks.cn/matlabcentral/answers/1815215-cant-seem-to-make-the-background-fully-black

编辑： Matt J 2022-10-1

I have uploaded two images, one is the original image and the other one is a processed image. i am wondering how can i make the background fully black because i cant seem to make the bottom right fully black in the processed image. i have processed the image by thresholding, binarising and inverting it.

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Answer 1

Matt J 2022-9-30

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编辑：Matt J 2022-9-30

在 MATLAB Online 中打开

A=imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1141370/original.png');

B=imquantize(A,multithresh(A,3));

C=1;

for i=1:4

C=C & ~bwareafilt(B==i,[80000,inf]);

end

imshow(C,[])

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Pravindkumaran Baskaran 2022-9-30

thank you very much !

Image Analyst 2022-10-1

在 MATLAB Online 中打开

If you want the shapes to have their original gray level and class (like uint8 or uint16), instead of being a binary (logical) image, you can use that mask to set the background to zero and leave the original gray levels untouched:

% Blacken background:
A(~C) = 0;

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Answer 2

Image Analyst 2022-9-30

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Looks a lot like homework. Is it?

What I'd try first is to create a background and then subtract it from the image. You can construct a background by getting the values along the edges, or the corners and then using biliear interpolation, like with interp1 to build the background. Should be easy - try it.