How to extract the blob of gray image ?
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Jenifer NG
le 18 Fév 2023
Commenté : Jenifer NG
le 23 Fév 2023
Dear All ,
I want to extract blob of this image then measure the maximum major length.
I try some method but is is not work.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1299350/image.gif)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1299355/image.png)
here is my code:
clc
clear
X = imread('img.tif')
X = imadjust(X);
% Threshold image - manual threshold
BW = im2gray(X) > 0;
% Open mask with disk
radius = 3;
decomposition = 0;
se = strel('disk', radius, decomposition);
BW = imopen(BW, se);
% Close mask with disk
radius = 5;
decomposition = 0;
se = strel('disk', radius, decomposition);
BW = imclose(BW, se)*255;
% imshow(BW)
props = regionprops(BW,'MajorAxisLength','BoundingBox')
[max_length, idx] = max([props.MajorAxisLength]);
% Get the bounding box of the biggest blob
bbox = props(idx).BoundingBox;
% Plot the rectangle around the biggest blob
figure;
imshow(BW);
hold on;
rectangle('Position', bbox, 'EdgeColor', 'r', 'LineWidth', 2);
Thanks and Regards!
Han
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Réponse acceptée
Image Analyst
le 19 Fév 2023
I'd try some denoising first, like medfilt2 or imnlmfilt. Then I'd try adjusting the thresholds with my interactive thresholding app:
Then use bwferet. Don't use MaxAxisLength of regionprops since that gives you the max axis length of an ellipse fitted to the shape rather than the actual caliper distance like bwferet gives you.
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