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How to improve the image

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I need to improve an image

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Rik on 11 Jun 2020
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Question title:
How to improve the filtering of a bubble image
Question body:
I need to better filter my image (a bubble) in order to obtain a better filtering than the one I already have (code), in order to get a better approximation of the contour of the bubble.
Would you know of any other filters or what I could change in my code to improve the borders I drew in red and to make the filtered image of the bubble (image 2) better look like the real bubble outline? (it should look like a semi-ellipse)
Thanks in advance
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% 1 - Reading the image
image = imread('bubble.png');
figure, imshow(image);
% 2 - Cropping the image
cropped = imcrop(image,[552.9 0 639.2 1080]);
figure, imshow(cropped);
% 3 - Gray scale
gray = rgb2gray(cropped);
figure, imshow(gray);
% 4 - Threshold filter
thresh = im2bw(gray, 0.5);
figure, imshow(thresh);
% 5 - Small pixel cluster removal filter
remove = bwareaopen(thresh, 13200);
figure, imshow(remove);
% 6 - Close connections filter
se = strel('line',300,0);
closing = imclose(remove,se);
figure, imshow(closing);
% 7 - Fill center of objects filter
OriginalLine = closing(1 , :);
OriginalLine2 = closing(end , :);
closing(1, :) = true;
closing(end, :) = true;
fill = imfill(closing, 'holes');
closing(end,:) = false;
closing(1,:) = false;
fill(1, :) = OriginalLine;
fill(end, :) = OriginalLine2;
figure, imshow(fill);

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Accepted Answer

Image Analyst
Image Analyst on 17 Apr 2020
Can you assume the ellipse axes will be vertical and horizontal? If not, see the FAQ: Click here
Otherwise you can use bwferet() to get the caliper dimension in one direction. Call it 2*a. Use sum() or regionprops() to get the area and centroid,
binaryImage = bwareafilt(binaryImage, 1); % Take largest blob only.
props = regionprops(binaryImage, 'Area', 'Centroid');
area = props.Area;
xCenter = props.Centroid(1);
yCenter = props.Centroid(2);
hold on;
plot(xCenter, yCenter, 'r+', 'MarkerSize', 60, 'LineWidth', 2); % Plot crosshairs at the centroid.
then, since the area of an ellipse is pi*a*b,
b = area / (pi * a);
Create an ellipse from the code in the FAQ:
xCenter = 12.5;
yCenter = 10;
xRadius = 2.5;
yRadius = 8;
theta = 0 : 0.01 : 2*pi;
x = xRadius * cos(theta) + xCenter;
y = yRadius * sin(theta) + yCenter;
plot(x, y, 'LineWidth', 3);
grid on;
where xRadius = b and yRadius = a (if vertical is the feret diameter direction you picked).
Or you might try activecontour(). See attached demo.


Image Analyst
Image Analyst on 18 Apr 2020
You have an old version then. Try using regionprops() and getting the MajorAxisLength and MinorAxisLength, which are the axes of an ellipse fit to your blob.
Image Analyst
Image Analyst on 18 Apr 2020
See step by step instructions in Steve's Image Processing Blog.

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