Search code examples
matlabfits

How to remove stars and other objects from a galaxy FITS image using Matlab?

I have the following image in fits format. I want to remove all the stars and other smaller dots from that image using matlab.enter image description here

I performed the following matlab operations to remove stars in it. 

I = imread('NGC_0253.jpg');
if size(I,3)==3
   I=rgb2gray(I);
end
K = imcomplement(I);
L = I-K;
M = medfilt2(L);
imshow(M)

I am getting image like this:enter image description here

I also try the following:

I = imread('NGC_0253.jpg');
if size(I,3)==3
   I=rgb2gray(I);
end
K = imcomplement(I);
L = I-K;
M = bwareaopen(L,1000);
N = medfilt2(M);
imshow(N)

but it also does not satisfy me:enter image description here

Which is not my objective. My objective is to remove all the stars from the image.

So, What should I do to remove all the stars leaving the galaxy intact from the image?

Solution

  • By using bwareaopen I get a good result. (I use your second image as input, so you can keep the first part of your code) 

    I = imread('NGC_0253.jpg');
I = im2bw(I,0.5); %the second parameter correspond to the threshold ∈ [0-1]
I = ~bwareaopen(~I,400); %where 400 = the minimal number of connected pixel needed to not be removed.

imshow(I)

    INPUT:

    enter image description here

    OUTPUT:

    enter image description here

    Improvement:

    To be more precise it can be useful to compute the parameters of the ellipse.

    enter image description here

    To do that you can use the function fit_ellipse available on fileexchange.

    Iedge = edge(mat2gray(I),'Canny');
[x,y] = find(Iedge');
hold on
A = fit_ellipse(x,y,h);