i have detected a object in a scene image , now i want to find centroid coordinates of this object in a whole image . How do i get this ?

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Avinash Andhale
Avinash Andhale 2017-12-1
回答： Image Analyst 2023-9-29
A = imread('11.jpg');
boxImage=rgb2gray(A);
figure;
imshow(boxImage);
title('Image of a Object to be Detected');
B = imread('2.jpg');
sceneImage=rgb2gray(B);
figure;
imshow(sceneImage);
title('Image of a Cluttered Scene');
boxPoints = detectSURFFeatures(boxImage);
scenePoints = detectSURFFeatures(sceneImage);
figure;
imshow(boxImage);
title('100 Strongest Feature Points from Object Image');
hold on;
plot(selectStrongest(boxPoints, 100));
figure;
imshow(sceneImage);
title('300 Strongest Feature Points from Scene Image');
hold on;
plot(selectStrongest(scenePoints, 300));
[boxFeatures, boxPoints] = extractFeatures(boxImage, boxPoints);
[sceneFeatures, scenePoints] = extractFeatures(sceneImage, scenePoints);
boxPairs = matchFeatures(boxFeatures, sceneFeatures);
matchedBoxPoints = boxPoints(boxPairs(:, 1), :);
matchedScenePoints = scenePoints(boxPairs(:, 2), :);
figure;
showMatchedFeatures(boxImage, sceneImage, matchedBoxPoints, ...
matchedScenePoints, 'montage');
title('Putatively Matched Points (Including Outliers)');
[tform, inlierBoxPoints, inlierScenePoints] = ...
estimateGeometricTransform(matchedBoxPoints, matchedScenePoints, 'affine');
figure;
showMatchedFeatures(boxImage, sceneImage, inlierBoxPoints, ...
inlierScenePoints, 'montage');
title('Matched Points (Inliers Only)');
boxPolygon = [1, 1;... % top-left
size(boxImage, 2), 1;... % top-right
size(boxImage, 2), size(boxImage, 1);... % bottom-right
1, size(boxImage, 1);... % bottom-left
1, 1]; % top-left again to close the polygon
newBoxPolygon = transformPointsForward(tform, boxPolygon);
figure;
imshow(sceneImage);
hold on;
line(newBoxPolygon(:, 1), newBoxPolygon(:, 2), 'Color', 'y');
title('Detected Box');
plot(centroids(:,1), centroids(:,2), 'b*');
hold off

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回答（2 个）

Brahmadev
Brahmadev 2023-9-29
Hi Avinash,
You can find the centroid of the detected image using the following code:
% Defining a polygon of Datatype polyshape for use in "centroid" as input
polyin = polyshape(newBoxPolygon(1:4, 1),newBoxPolygon(1:4, 2));
% Finding the centroid
[centroidPosX, centroidPosY] = centroid(polyin);
hold on
plot(centroidPosX, centroidPosY, "ro") % Plotting the centroid in the same figure
You can refer to the following documentation for more information on the “centroid” function:
https://www.mathworks.com/help/matlab/ref/polyshape.centroid.html
Hope this helps in finding the centroid!
Image Analyst
Image Analyst 2023-9-29
See my Image Segmentation Tutorial in my File Exchange:
Image Analyst's File Exchange
It's a generic, general purpose demo of how to threshold an image to find blobs, and then measure things about the blobs (like centroid and bounding box, etc.), and extract certain blobs based on their areas or diameters.

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