how to measure boundary length in a binary image?

Hi,

I am trying to measure the total boundary length of the binary image in the following link: https://www.dropbox.com/s/9t86e3s6v6b002h/image.JPG?dl=0

I have tried bwperim, bwarea and regionprops( BW ,'perimeter'), but seems none of them gives an accurate result. I think the hard point in my case is to measure the real length of a inclined line. For example, the actual length of ([0 0 1 1]; [0 1 1 0]; [1 1 0 0]) is 1+2sqrt(2)+1 pixels instead of 6. Function regionprops( BW ,'perimeter') seems working well for closed boundary, but gives unexpected result for disclosed ones. Is there existing functions I can directly use for my case, or you have some other wise methods to address my problem? Thanks a lot forehead.

Answer 1

[Rahul punk]

boundaries = bwboundaries(binaryImage);

x = boundaries(:, 1);

y = boundaries(:, 2);

maxDistance = -inf;

for index1 = 1 : length(x)

for index2 = 1 : length(y)

deltaX = x(index1) - x(index2);

deltaY = y(index1) - y(index2);

distance = sqrt(deltaX^2+deltaY^2);

if distance > maxDistance

Answer 2

[Rahul punk]

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 short g;

format compact;

fontSize = 25;

%===============================================================================

% Get the name of the image the user wants to use.

baseFileName = 'image.JPG';

baseFileName = 'image1.JPG';

% Get the full filename, with path prepended.

folder = []; % Determine where demo folder is (works with all versions).

fullFileName = fullfile(folder, baseFileName);

%===============================================================================

% Read in a demo image.

grayImage = 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(grayImage)

if numberOfColorChannels > 1

% It's not really gray scale like we expected - it's color.

% Use weighted sum of ALL channels to create a gray scale image.

grayImage = rgb2gray(grayImage);

% ALTERNATE METHOD: Convert it to gray scale by taking only the green channel,

% which in a typical snapshot will be the least noisy channel.

% grayImage = grayImage(:, :, 2); % Take green channel.

end

% Display the image.

subplot(2, 2, 1);

imshow(grayImage, []);

axis on;

axis image;

caption = sprintf('Original Gray Scale Image');

title(caption, 'FontSize', fontSize, 'Interpreter', 'None');

drawnow;

hp = impixelinfo();

% 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', 'Rahul', 'NumberTitle', 'Off')

drawnow;

% binarize the image.

binaryImage = imbinarize(grayImage);

% Make sure there is only one blob

binaryImage = bwareafilt(binaryImage, 1);

% Display the image.

subplot(2, 2, 2);

imshow(binaryImage, []);

axis on;

axis image;

caption = sprintf('Binary Image');

title(caption, 'FontSize', fontSize, 'Interpreter', 'None');

drawnow;

hp = impixelinfo();

% Label the image

labeledImage = bwlabel(binaryImage);

% Make measurements of bounding box

props = regionprops(labeledImage, 'BoundingBox');

width = props.BoundingBox(3);

height = props.BoundingBox(4);

% Display it with the box overlaid on it.

subplot(2, 2, 3);

imshow(grayImage, []);

axis on;

axis image;

caption = sprintf('Gray Scale Image with box overlaid');

title(caption, 'FontSize', fontSize, 'Interpreter', 'None');

drawnow;

hp = impixelinfo();

hold on;

rectangle('Position', props.BoundingBox, 'EdgeColor', 'r', 'LineWidth', 2);

message = sprintf('The width = %f.\nThe height = %f', width, height);

uiwait(helpdlg(message));