This would be more accurate if you used a black velvet fabric behind your tile. Then you'd simply threshold and call bwboundaries() or bwperim(). You can still try it with a gray background like you have but your edge may not be as sharp and linear. But try this demo code on your image:
clc;
clearvars;
close all;
workspace;
fontSize = 20;
% Read in a tile color demo image.
folder = 'C:\Users\Kurniawan\Documents';
baseFileName = 'tile.jpg';
fullFileName = fullfile(folder, baseFileName);
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
% Didn't find it there. Check the search path for it.
fullFileName = baseFileName; % No path this time.
if ~exist(fullFileName, 'file')
% Still didn't find it. Alert user.
errorMessage = sprintf('Error: %s does not exist.', fullFileName);
uiwait(warndlg(errorMessage));
return;
end
end
rgbImage = imread(fullFileName);
% Get the dimensions of the image. numberOfColorBands should be = 3.
[rows columns numberOfColorBands] = size(rgbImage);
% Display the original color image.
subplot(2, 2, 1);
imshow(rgbImage, []);
title('Original Color Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Extract the individual red, green, and blue color channels.
% redChannel = rgbImage(:, :, 1);
% greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
subplot(2, 2, 2);
imshow(blueChannel, []);
title('Blue Channel Image', 'FontSize', fontSize);
% Threshold blue channel
binaryImage = blueChannel < 163;
% Get rid of small blobs.
binaryImage = bwareaopen(binaryImage, 10000);
% Fill in any holes in the tile.
binaryImage = imfill(binaryImage, 'holes');
% Display it.
subplot(2, 2, 3);
imshow(binaryImage, []);
title('Binary Image', 'FontSize', fontSize);
% Get the boundary coordinates
tileBoundary = bwboundaries(binaryImage);
% Plot boundaries over original image.
subplot(2, 2, 4);
imshow(rgbImage, []);
title('Original Color Image with Boundary', 'FontSize', fontSize);
hold on;
thisBoundary = tileBoundary{1};
xCoordinates = thisBoundary(:, 2);
yCoordinates = thisBoundary(:, 1);
plot(xCoordinates, yCoordinates, 'b-', 'LineWidth', 3);
