How to find the center of 4 points on an image?

Question

Milad Zarei 2020-4-14

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https://ww2.mathworks.cn/matlabcentral/answers/517942-how-to-find-the-center-of-4-points-on-an-image

评论： Ameer Hamza 2020-4-16

I have an image of the foot that was devided into different cells. I need to find the center of each cell. I was wondering if the best way to do so is to pick the 4 points on the vertices of the cell and let Matlab find the center?

Attache is the image. Let me know if you have any ideas. Thanks.

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Tommy 2020-4-14

You could create a polyshape based on the four vertices and then use centroid.

Milad Zarei 2020-4-15

Yes, I think that would work. I'll give it a shot. Thanks!

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Answer 1

Ameer Hamza 2020-4-15

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/517942-how-to-find-the-center-of-4-points-on-an-image#answer_426163

编辑：Ameer Hamza 2020-4-15

在 MATLAB Online 中打开

try this code. It requires functions from image preocessing toolbox.

im = im2double(imread('image.jpeg'));
%% remove red text
im_gray = rgb2gray(im);
im_gray(~(im_gray < 0.2)) = 1;
im_gray = double(imbinarize(im_gray));
%% find the polygons
regions = bwconncomp(im_gray);
pxlList = regions.PixelIdxList;
outlier = isoutlier(cellfun(@(x) numel(x), pxlList));
pxlList(outlier) = [];
%% find centers
centers = zeros(numel(pxlList), 2);
for i=1:numel(pxlList)
    im_zeros = zeros(size(im_gray));
    im_zeros(pxlList{i}) = 1;
    rp = regionprops(im_zeros);
    centers(i, :) = rp.Centroid;
end
%%
imshow(im);
hold on
plot(centers(:,1), centers(:,2), 'r+', 'LineWidth', 2, 'MarkerSize', 10);

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Image Analyst 2020-4-15

编辑：Image Analyst 2020-4-15

在 MATLAB Online 中打开

point_line_distance.m

Coordinate system is in pixels, or matrix indexes. So like any matrix, (1,1) is in the upper left, and row indexes increase going down, and column indexes increase going across from left to right.

To get the point to line distance, see the function below, and the attached script for a full demo.

% Get the distance from a point (x3, y3) to
% a line defined by two points (x1, y1) and (x2, y2);
% Reference: http://mathworld.wolfram.com/Point-LineDistance2-Dimensional.html
function distance = GetPointLineDistance(x3,y3,x1,y1,x2,y2)
try
	
	% Find the numerator for our point-to-line distance formula.
	numerator = abs((x2 - x1) * (y1 - y3) - (x1 - x3) * (y2 - y1));
	
	% Find the denominator for our point-to-line distance formula.
	denominator = sqrt((x2 - x1) ^ 2 + (y2 - y1) ^ 2);
	
	% Compute the distance.
	distance = numerator ./ denominator;
catch ME
	callStackString = GetCallStack(ME);
	errorMessage = sprintf('Error in program %s.\nTraceback (most recent at top):\n%s\nError Message:\n%s',...
		mfilename, callStackString, ME.message);
	WarnUser(errorMessage)
end
return; % from GetPointLineDistance()
end