Detect the shape in MATLAB

Question

Med Future 2022-3-15

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https://ww2.mathworks.cn/matlabcentral/answers/1672399-detect-the-shape-in-matlab

评论： Image Analyst 2022-3-25

image_2732.png

Hello, I hope you are doing well.

I have the image of 1000x1000.I have attached the image below I want to detect the number of lines in the image and pixel value of each line. How can i do it in MATLAB

as you can see in image, there is four lines, is Hough transform work on this or any image processing.

For example line is at 720, then it show pixel value 720

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Jan 2022-3-15

Are the lines parallel to the X axis in all cases? Then there are much cheaper methods than a Hough transformation.

Med Future 2022-3-16

Yes line are Parallel. Then how can i detect?

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Answer 1

Image Analyst 2022-3-15

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https://ww2.mathworks.cn/matlabcentral/answers/1672399-detect-the-shape-in-matlab#answer_918544

在 MATLAB Online 中打开

% Make the image binary, if it's not already.
binaryImage = grayImage > 128;
% Count the lines.
[LabeledImage, numLines] = bwlabel(binaryImage);

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Image Analyst 2022-3-16

在 MATLAB Online 中打开

OK, here is a full demo. Tell me if this is what you want:

% Demo by Image Analyst
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 = 22;
markerSize = 40;
%--------------------------------------------------------------------------------------------------------
%    READ IN IMAGE
folder = pwd;
baseFileName = 'image_2732.png';
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);
% Get the dimensions of the image.
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(rgbImage)
if numberOfColorChannels > 1
    % It's not really gray scale like we expected - it's color.
    fprintf('It is not really gray scale like we expected - it is color\n');
    % Extract the blue channel.
    grayImage = rgbImage(:, :, 3);
else
    grayImage = rgbImage;
end
%--------------------------------------------------------------------------------------------------------
% Display the image.
subplot(2, 1, 1);
imshow(grayImage);
impixelinfo;
axis('on', 'image');
title('Original Gray Scale Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Maximize window.
g = gcf;
g.WindowState = 'maximized';
drawnow;
%--------------------------------------------------------------------------------------------------------
% Binarize the image to get a mask.
mask = grayImage >= 128;
% Display mask image.
subplot(2, 1, 2);
imshow(mask);
hold on;
impixelinfo;
axis('on', 'image');
drawnow;
title('Binary Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Get a labeled image and count of the number of distinct regions.
[labeledImage, numRegions] = bwlabel(mask);
caption = sprintf('Binary Image with %d lines', numRegions);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
% Get all the blob properties.  Can only pass in originalImage in version R2008a and later.
props = regionprops(labeledImage, 'Area', 'Centroid');
allLengths = [props.Area]
centroids = vertcat(props.Centroid);
% Put a thick red line wherever there is a line.  This is because on the figure the lines are so thin they're not visible.
hold on;
for k = 1 : numRegions
    x1 = centroids(k, 1) - allLengths(k)/2;
    if x1 < 1
        x1 = 1;
    elseif x1 > columns
        x1 = columns;
    end
    y1 = centroids(k, 2);
    x2 = centroids(k, 1) + allLengths(k)/2;
    if x2 < 1
        x2 = 1;
    elseif x2 > columns
        x2 = columns;
    end
    y2 = y1; % Assumes perfectly horizontal lines.
    plot([x1,x2], [y1,y2], 'r-', 'LineWidth', 4);
    xt = props(k).Centroid(1);
    yt = props(k).Centroid(2);
    str = sprintf('Length = %d at line %d', allLengths(k), y1);
    text(xt, yt, str, 'Color', 'r', 'FontWeight', 'bold', 'HorizontalAlignment', 'Center', 'VerticalAlignment','bottom', 'FontSize',15);
end
hold off;
% Tell the user
message = sprintf('Done!\n');
uiwait(helpdlg(message))

Image Analyst 2022-3-19

在 MATLAB Online 中打开

testGrayImage.m

Then don't plot individual ones in the loop and call yline() after the loop. Solution attached.

% Put a thick red line wherever there is a line.  This is because on the figure the lines are so thin they're not visible.
hold on;
for k = 1 : numRegions
    x1 = centroids(k, 1) - allLengths(k)/2;
    if x1 < 1
        x1 = 1;
    elseif x1 > columns
        x1 = columns;
    end
    y1 = centroids(k, 2);
    x2 = centroids(k, 1) + allLengths(k)/2;
    if x2 < 1
        x2 = 1;
    elseif x2 > columns
        x2 = columns;
    end
    y2 = y1; % Assumes perfectly horizontal lines.
    % 	plot([x1,x2], [y1,y2], 'r-', 'LineWidth', 4);
    % 	xt = props(k).Centroid(1);
    % 	yt = props(k).Centroid(2);
    % 	str = sprintf('Length = %d at line %d', allLengths(k), y1);
    % 	text(xt, yt, str, 'Color', 'r', 'FontWeight', 'bold', 'HorizontalAlignment', 'Center', 'VerticalAlignment','bottom', 'FontSize',15);
end
hold off;
% Get the row number the white lines are on
whiteLineRows1 = centroids(:, 2)
% Some of the lines are separated but are on the same line.
% The poster wants any on the same line to be considered as they are on the same line.
% To do that use unique.
whiteLineRows2 = unique(whiteLineRows1)
hold on;
yline(whiteLineRows2, 'LineWidth', 2, 'Color', 'r');

Med Future 2022-3-25

@Image Analyst Thanks for your answer , Like in first image i have half lines and in second image i have full lines , i just want this algo to be that if half line comes it detect half lines and plot y axis half lines as you shared above, if full lines image comes it draw full lines image. the rest of the things are fine.

Image Analyst 2022-3-25

I've given it to you both ways. First I found line segments, with the starting and ending points, then you said you wanted "only unique lines" so if two blobs were on the same line/row, I used unique() to get only unique lines. So if two blobs were on the same row, I'd draw only one line across the whole row. So now you have it both ways. Does that not solve the problem?

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Answer 2

yanqi liu 2022-3-16

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1672399-detect-the-shape-in-matlab#answer_918704

在 MATLAB Online 中打开

img = imread('https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/928244/image_2732.png');

bw = im2bw(img);

% 霍夫分析

[H,T,R] = hough(bw);

P = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));

lines = houghlines(bw,T,R,P,'FillGap',5,'MinLength',7);

max_len = 0;

line_r = [];

figure; imshow(img, []); hold on;

for k = 1:length(lines)

xy = [lines(k).point1; lines(k).point2];

plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','cyan');

p = [];

xy = round(xy);

for j = min(xy(:,1)) : max(xy(:,1))

p = [p img(xy(1,2), j)];

end

text(xy(1,1),xy(1,2)-15, sprintf('pixel value = %.2f', mean(p)), 'color', 'r');

end

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Med Future 2022-3-19

@Image Analyst dont understand you answer.

Image Analyst 2022-3-19

Sorry - I put it in the wrong place. it was meant to be a reply to your comment to me

https://www.mathworks.com/matlabcentral/answers/1672399-detect-the-shape-in-matlab#comment_2052194

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