MATLAB: Adding trendline to a plot

adding trendline

Good Day,

Please how do I add trendline(s) to a certain straight line portion(s) of a plot and how to extend the trendline to touch y and or x axis and the y and or x axis value determined?

Another related question is that how do I insert horizontal line on a plot and extend it to touch y axis and the y axis value determined?

Thanks

Best regards,

Isa

Best Answer

I'd fit the portion of the data you're interested in to a line using polyfit. Then use polyval to get the points on the line over the entire range that you're interested in. See this demo:

clc;    % Clear the command window.
workspace;  % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 20;
% Define equation.
x = -2:20;
y = (x-2).^2;
% Plot it
plot(x,y, 'bo-', 'LineWidth', 3);
grid on;
title('y = (x-2).^2', 'FontSize', fontSize);
xlabel('X', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Give a name to the title bar.
set(gcf,'name','Demo by ImageAnalyst','numbertitle','off') 
% Fit the range fro 10 to 20 with a line.
limitedRange = 10:20;
coeffs = polyfit(x(limitedRange), y(limitedRange), 1)
% Define the range where we want the line
xFitting = 0:19; % Or wherever...
yFitted = polyval(coeffs, xFitting);
% Plot the fitted line over the specified range.
hold on; % Don't blow away prior plot
plot(xFitting, yFitted, 'ro-', 'LineWidth', 2);
legend('Original Data', 'Line Fit');

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% Define sample data.
X = [1,2,3,4,5,6,7,8,9];
Y = [4 5 6 9 8 7 4 1 2];
% Do the plotting:

plot(X, Y, 'bo', 'LineWidth', 3, 'MarkerSize', 15);
grid on;
% Maximize the figure window.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Label the various parts of the plot.
fontSize = 20;
title('lowcalorie Plot', 'FontSize', fontSize);
xlabel('X', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);
coefficients = polyfit(X, Y, 1);
fittedY = polyval(coefficients, X);
hold on;
% Do the plotting:
plot(X, fittedY, 'rs-', 'LineWidth', 3, 'MarkerSize', 15);
legend('Y', 'Fitted Y');

MATLAB: Fill a gap on an image surface

Can you threshold it? If that gives an OK boundary except for that gap, then use the boundary() function.

Try this:

clc;    % Clear the command window.
clear all;
close all;  % Close all figures (except those of imtool.)
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;
%===============================================================================
% Get the name of the image the user wants to use.
baseFileName = 'bone_image.jpeg';
folder = pwd;
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
%=======================================================================================
% Read in demo image.
grayImage = imread(fullFileName);
% Get the dimensions of the image.
[rows, columns, numberOfColorChannels] = size(grayImage)
if numberOfColorChannels > 1
	grayImage = rgb2gray(grayImage);
end
% Display image.

subplot(2, 2, 1);
imshow(grayImage, []);
impixelinfo;
axis on;
caption = sprintf('Original Image\n%s', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0.05 1 0.95]);
% 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')
drawnow;
% Crop off white frame surrounding the image.
grayImage = grayImage(5:645, 6:647);
%===================================================================================
% Get a histogram
subplot(2, 2, 2);
histogram(grayImage);
grid on;
title('Histogram of gray scale image', 'FontSize', fontSize, 'Interpreter', 'None');
% Convert to binary
% binaryImage = imbinarize(grayImage);
binaryImage = grayImage > 50;
% Fill blob and take the largest one.
binaryImage = bwareafilt(imfill(binaryImage, 'holes'), 1);
% Display image.
subplot(2, 2, 3);
imshow(binaryImage, []);
impixelinfo;
axis on;
title('Original Boundary', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
% Get outline
boundaries = bwboundaries(binaryImage);
x = boundaries{1}(:, 2);
y = boundaries{1}(:, 1);
hold on;
plot(x, y, 'r-', 'LineWidth', 3);
% Get the boundary
b = boundary(x, y, 0.9);
subplot(2, 2, 4);
imshow(binaryImage);
hold on;
plot(x(b), y(b), 'r-', 'LineWidth', 3);
axis image; % Make sure image is not artificially stretched because of screen's aspect ratio.
caption = sprintf('Boundary without Gap.');
title(caption, 'FontSize', fontSize);

Best Answer

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MATLAB: Linear regression

MATLAB: Fill a gap on an image surface

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