Remove inner part of the Image

Question

Alina tom 2018-7-4

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https://ww2.mathworks.cn/matlabcentral/answers/408695-remove-inner-part-of-the-image

评论： Image Analyst 2018-7-6

Desktop.zip

Hi All

I have multiple images and I want to remove the inner part the image but don't know how I can remove this.by using mask or any other approach ? Can anybody help me with this

these are some image . and I want a unique approach that work for all the images,some of the images are attached

1st one in input and second one is like output

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Answer 1

Oindri 2018-7-4

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Hi, You may try, first detecting the edge of the inner circle because its abrupt change in intensity, which will be easily detectable. Once you have defined that boundary, replace all internal pixels with black pixels. Given the varied nature of boundary, apply automatic detection of boundary.

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Alina tom 2018-7-4

can you please help me with some code

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Answer 2

KSSV 2018-7-4

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编辑：KSSV 2018-7-4

在 MATLAB Online 中打开

files = dir('*JPG') ;
nx = 512 ;  ny = 512 ;
N = length(files) ;
I = cell(N,1) ;
for i = 1:N
    I{i} = imread(files(i).name);
    I{i} = imresize(I{i},[nx ny]) ;        
end
C = round([nx ny]/2) ;  % center of the image 
R = 60. ;     % radius of circle 
th = linspace(0,2*pi,500) ;
xc = C(1)+R*cos(th) ;
yc = C(1)+R*sin(th) ;
%
I2 = cell(N,1) ;
x = 1:ny ; y = 1:nx ;
[X,Y] = meshgrid(x,y) ;
idx = inpolygon(X(:),Y(:),xc,yc) ;
for i = 1:N
    T = I{i}(:,:,1) ;
    T(idx) = 10 ;
    I2{i} = repmat(T,1,1,3) ;
    imshow(I2{i})
end

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KSSV 2018-7-4

YOu play with the radius of circle.......R can be fixed to 35..check

Alina tom 2018-7-4

the output is wrong by changing radius . I have tried this approach but not working for my case

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Answer 3

Image Analyst 2018-7-4

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testGrayImage.m

The attached algorithm seem to work with both your images. The function findcircles() didn't seem to work, so I thresholded followed by repeated erosions until the background and inner zone separated into two regions, then took the inner region and expanded it back out and used it as a mask to erase the inner zone of the gray scale image. You can adjust stepSize to erase a little closer to the inner boundary if you want.

Results for the first image:

And for the other image:

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Alina tom 2018-7-5

yes they are irregular shapes , the bright blob changing its position randomly that's why its difficult to remove . I have used convex hull but results are same.

Image Analyst 2018-7-6

freehand_masking_demo.m

You can use imfreehand() to lasoo the occasional photo that it didn't work for. See my attached demo. Otherwise it will take you quite a bit of work to make it more automatic. It will be tricky and could take a bit of time to develop the algorithm. You could consider hiring someone if you can't do it yourself. Or else contact the Mathworks and they'll do it for you.

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