Detect and Fill Edges of a Binary Image

I have this image that I have created from a point cloud. I want to connect the inner and outer rings and fill the region between them with 1s. Any suggestions? I tried creating a boundary of the scatter data, but I couldn't enclose the region with that. I can't use bwboundary because the points aren't currently connected. I would love to connect them then use that function if possible.

Answer 1

[Akira Agata]

Assuming that the inner/outer ring can be approximated by the edge of convex hull of inner/outer ring points, the area between inner and outer ring can be extracted by the following:

% Read and prepare the binary image
I = imread('Slice.jpg');
Igray = rgb2gray(I);
BWin = imbinarize(Igray);
BWin = imclearborder(BWin);

% Convex hull of outer ring points
CH1 = bwconvhull(BWin);

% Remove outer ring points
se = strel('disk',10);
CH1b = imerode(CH1,se);
BW1 = BWin & CH1b;

% Convex hull of inner ring points
CH2 = bwconvhull(BW1);

% Extract the area between inner and outer convex hull
BWout = CH1 - CH2;

% Show the result
figure
imshowpair(BWin,BWout)