Filling ellipse fit with white, and making the rest of the image black

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med-sweng 2014-11-24

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https://ww2.mathworks.cn/matlabcentral/answers/164086-filling-ellipse-fit-with-white-and-making-the-rest-of-the-image-black

回答： DGM 2023-4-30

If you run the code here, you will get a best ellipse fit with green borders.

I know how to fill the ellipse with white for instance, but, I have some white pixels coming out off the ellipse best fit. How can I get rid of those small white pixels appearing outside the ellipse, and make the rest of the image black?

It seems if we use im2bw, some information will be lost.

Thanks.

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Answer 1

Image Analyst 2014-11-24

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Get a binary image (mask) of where the ellipse is. So it's true inside the ellipse and false outside. Then to zero out the pixels in the gray scale image outside the ellipse mask, simply do:

grayImage(~binaryEllipseMask) = 0;

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med-sweng 2014-11-24

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Thanks for your kind reply.

Can you just kindly clarify your point:

Get a binary image (mask) of where the ellipse is

I don't think this will be done with im2bw? Right? Should I here explicitly determine the location of the ellipse?

med-sweng 2014-11-24

Also, would that be a manual process? Not an automatic one then?

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Answer 2

DGM 2023-4-30

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See the attached function conic2mask(). The only effective difference between conic2mask() and DrawConic() is the change of a single line. Other than that, I replaced the synopsis since the original was simultaneously undescriptive and wrong. Everything else in the package needs documentation and cleanup.

img = imread('rice.png');

E = FindEllipses(img);

outsize = size(img);

mask = false(outsize(1:2));

for k = 1:size(E,1)

thismask = conic2mask(E(k,:),outsize);

mask = mask | thismask; % the union of masks

end

imshow(mask,'border','tight')