I want to detect the slopes of all the lines in a pattern. Is it possible? I am new to MATLAB. Can anyone help?

[Rik]

Do you want the slope of every separate line or the average slope of all lines?

And what have you tried so far?

[Muhammed Shebeeb Cherum Kuzhi]

I want slope of all lines as a list.

[Muhammed Shebeeb Cherum Kuzhi]

I got this code for getting slope of a single line. But not working for mine.

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 14;
rgbImage = imread('abc.jpg');
% Display the image.
subplot(1, 2, 1);
imshow(rgbImage, []);
title('Original RGB JPEG Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off') 
grayImage = rgb2gray(rgbImage);
binaryImage = grayImage ~= 255;
% Display the image.
subplot(1, 2, 2);
imshow(binaryImage, []);
title('Binary Image showing horrible JPEG artifacts and fitted line', 'FontSize', fontSize, 'Interpreter', 'None');
% Find locations of pixels
[y, x] = find(binaryImage);
% Do the fit to a line:
coefficients = polyfit(x, y, 1)
slope = coefficients(1);
intercept = coefficients(2);
message = sprintf('The slope of the line is %f.\nThe intercept is %f',...
  slope, intercept);
helpdlg(message);
% Make a fitted line
x1 = min(x)
x2 = max(x)
xFit = x1:x2;
yFit = polyval(coefficients, xFit);
hold on;
plot(xFit, yFit, 'r-', 'LineWidth', 2);
axis on;

[Rik]

You will first have to detect each line, so you will have to find a way to make only the pixels of a single line be 1. Then you can use the method Image Analyst suggested (based on the header this looks like one of his demos).

Answer 1

[Image Analyst]

That code was meant for finding the angle of just one blob. If you have multiple blobs, use regionprops() and ask for the Orientation:

% Demo by Image Analyst.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clearvars;
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;
fprintf('Beginning to run %s.m ...\n', mfilename);

%-----------------------------------------------------------------------------------------------------------------------------------
% Read in image.  This is a horrible image.  NEVER use JPG format for image analysis.  Use PNG, TIFF, or BMP instead.
folder = [];
baseFileName = 'blue stripes.jpeg';
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
	% The file doesn't exist -- didn't find it there in that folder.
	% Check the entire search path (other folders) for the file by stripping off the folder.
	fullFileNameOnSearchPath = baseFileName; % No path this time.
	if ~exist(fullFileNameOnSearchPath, 'file')
		% Still didn't find it.  Alert user.
		errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
		uiwait(warndlg(errorMessage));
		return;
	end
end
rgbImage = imread(fullFileName);
[rows, columns, numberOfColorChannels] = size(rgbImage)
% Display the test image.
subplot(2, 2, 1);
imshow(rgbImage, []);
axis('on', 'image');
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
caption = sprintf('Original RGB Image : "%s"\n%d rows by %d columns', baseFileName, rows, columns);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.

% Set up figure properties:
% Enlarge figure to full screen.
hFig1 = gcf;
hFig1.Units = 'Normalized';
hFig1.WindowState = 'maximized';
% Get rid of tool bar and pulldown menus that are along top of figure.
% set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
hFig1.Name = 'Demo by Image Analyst';

[binaryImage,maskedRGBImage] = createMask(rgbImage);

% Get rid of blobs touching the border.
subplot(2, 2, 2);
imshow(binaryImage);
% Some stripes are broken.  Try to connect broken stripes.
binaryImage = imdilate(binaryImage, true(1, 10));
% Get convex hull and fill holes
binaryImage = bwconvhull(binaryImage, 'objects');
imshow(binaryImage);

% Get the area of the blobs
props = regionprops(binaryImage, 'Area');
allAreas = sort([props.Area])
% Now we know that blobs with area less than 1000 pixels are not full stripes.  Delete them
binaryImage = bwareafilt(binaryImage, [1000, inf]);
% Now small noise blobs are gone.

% Label each blob with 8-connectivity, so we can make measurements of it
[labeledImage, numberOfBlobs] = bwlabel(binaryImage, 8);
% Apply a variety of pseudo-colors to the regions.
coloredLabelsImage = label2rgb (labeledImage, 'hsv', 'k', 'shuffle');
% Display the pseudo-colored image.
imshow(coloredLabelsImage);
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
axis('on', 'image');
title('Final Mask Image', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;

% Get the centroids.
% Get all the blob properties.  Can only pass in originalImage in version R2008a and later.
props = regionprops(labeledImage, 'Centroid', 'Area', 'Orientation');
numberOfBlobs = size(props, 1);
allAreas = [props.Area]
allAngles = [props.Orientation]
xy = vertcat(props.Centroid)

% Plot cross hairs are every centroid.
hold on;
for k = 1 : numberOfBlobs
	plot(xy(k, 1), xy(k, 2), 'w+', 'LineWidth', 2);
end

% Compute the averate orientation.
aveAngle = mean(allAngles);
numStripes = length(allAngles);

% Show angles
subplot(2, 2, 3);
bar(allAngles, 1);
caption = sprintf('%d Individual Bar Angles.  The average angle is %.3f degrees', numStripes, aveAngle);
title(caption, 'FontSize', fontSize);
xlabel('Bar Number', 'FontSize', fontSize);
ylabel('Angle in Degrees', 'FontSize', fontSize);
grid on;
% Show average angle as a red line.
yline(aveAngle, 'Color', 'r', 'LineWidth', 2);

% Show angle distribution
subplot(2, 2, 4);
histogram(allAngles);
xlabel('Angle in Degrees', 'FontSize', fontSize);
ylabel('Count', 'FontSize', fontSize);
grid on;
caption = sprintf('Histogram of %d Angles.  The average angle is %.3f degrees', numStripes, aveAngle);
title(caption, 'FontSize', fontSize);
% Show average angle as a red line.
xline(aveAngle, 'Color', 'r', 'LineWidth', 2);

message = sprintf('Done!\nThe average angle is %.3f degrees', aveAngle)
msgbox(message);

function [BW,maskedRGBImage] = createMask(RGB)
%createMask  Threshold RGB image using auto-generated code from colorThresholder app.
%  [BW,MASKEDRGBIMAGE] = createMask(RGB) thresholds image RGB using
%  auto-generated code from the colorThresholder app. The colorspace and
%  range for each channel of the colorspace were set within the app. The
%  segmentation mask is returned in BW, and a composite of the mask and
%  original RGB images is returned in maskedRGBImage.

% Auto-generated by colorThresholder app on 22-Sep-2021
%------------------------------------------------------


% Convert RGB image to chosen color space
I = rgb2hsv(RGB);

% Define thresholds for channel 1 based on histogram settings
channel1Min = 0.425;
channel1Max = 0.567;

% Define thresholds for channel 2 based on histogram settings
channel2Min = 0.308;
channel2Max = 1.000;

% Define thresholds for channel 3 based on histogram settings
channel3Min = 0.000;
channel3Max = 0.785;

% Create mask based on chosen histogram thresholds
sliderBW = (I(:,:,1) >= channel1Min ) & (I(:,:,1) <= channel1Max) & ...
	(I(:,:,2) >= channel2Min ) & (I(:,:,2) <= channel2Max) & ...
	(I(:,:,3) >= channel3Min ) & (I(:,:,3) <= channel3Max);
BW = sliderBW;

% Initialize output masked image based on input image.
maskedRGBImage = RGB;

% Set background pixels where BW is false to zero.
maskedRGBImage(repmat(~BW,[1 1 3])) = 0;

end