MATLAB: Perimeter of a specific area

perimeterspecific region

Hi. I want to calculate the perimeter of the object below:

I used bwperim to get this:

but I really want is indeed the red region specified here (only the arc!):

How I can do so?

Can MATLAB automatically do it or I have to ask the user to select it?

Thanks so much!

Steven

Best Answer

First of all, invert and call bwareaopen() to get rid of the small specks, then invert to get back the original again. Then you can get a perimeter without the little noise bits.

But I wouldn't use bwperim because I'd want the boundary coordinates in order so I can find the kinks. So I'd use bwboundaries() to get the x,y coordinates in order as it goes around the curve.

Then you can use Roger Stafford's kink finding code in the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_find_.22kinks.22_in_a_curve.3F to find the 3 "kinks" in your curve. Once you know that, you can split up the boundary coordinates into 3 segments. Of course one of them will be on each end of the array. So you'll have (part of segment1),(all of segment2),(all of segment3),(remaining part of segment1) as you traverse the boundary coordinates. Does that make sense. Finally, for robustness you'll have to check for the case where a kink pixel lies exactly at the first coordinate. That's not too likely but if you want bulletproof code, you need to check for it and be prepared to handle that case.

Related Solutions

MATLAB: How to draw a circle on existed circle ? How to calculate the image shift in pixels from its center

You can use bwboundaries if all you want to do is draws outlines of the boundaries in the overlay above the original image:

format longg;
format compact;
clc;  % Clear command window.
workspace;  % Make sure the workspace panel is showing.
fontSize = 25;
% Read in a standard MATLAB gray scale demo image.
folder = 'C:\Users\Naresh\Documents\Temporary';
baseFileName = 'imfill.jpg';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
  % File doesn't exist -- 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 in the search path folders.', fullFileName);
    uiwait(warndlg(errorMessage));
    return;
  end
end
grayImage = imread(fullFileName);
% Get the dimensions of the image.  
% numberOfColorBands should be = 1.
[rows columns numberOfColorBands] = size(grayImage)
% Display the original gray scale image.

subplot(2, 2, 1);
imshow(grayImage, []);
axis square;
title('Original Grayscale Image', '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') 
% Create a binary image.
binaryImage = grayImage < 128;
subplot(2, 2, 2);
imshow(binaryImage);
axis square;
title('Binary Image', 'FontSize', fontSize);
% bwboundaries() returns a cell array, where each cell contains the row/column coordinates for an object in the image.
% Plot the borders of all the coins on the original grayscale image using the coordinates returned by bwboundaries.
% Display the original gray scale image.
subplot(2, 2, 3);
imshow(grayImage, []);
title('Original Grayscale Image with Outlines from bwboundaries()', 'FontSize', fontSize);
axis square;
hold on;
boundaries = bwboundaries(binaryImage);
numberOfBoundaries = size(boundaries, 1);
for k = 1 : numberOfBoundaries
  thisBoundary = boundaries{k};
  plot(thisBoundary(:,2), thisBoundary(:,1), 'r-', 'LineWidth', 3);
end
hold off;

MATLAB: Crop dark area and display the face only

Convert to grayscale and then threshold and find the bounding box

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
% Read in the color image.
folder = pwd;
baseFileName = 'm2.bmp';
% 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, 3, 1);
imshow(rgbImage, []);
axis on;
title('Original Color Image', 'FontSize', fontSize);
drawnow;
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Histogram the red channel, but there is a huge spike at 255 so let's not count those.
subplot(2, 3, 2);
grayImage = rgb2gray(rgbImage);
imshow(grayImage, []);
title('Gray Scale version', 'FontSize', fontSize);
subplot(2, 3, 3);
histogram(grayImage(grayImage<255))
grid on;
title('Histogram of Gray Scale Image', 'FontSize', fontSize);
someThresholdValue = 150;
binaryImage = grayImage > someThresholdValue;
% Take largest blob
binaryImage = bwareafilt(binaryImage, 1);
subplot(2, 3, 4);
imshow(binaryImage);
grid on;
title('Binary Image', 'FontSize', fontSize);
% Label the binary image.
labeledImage = bwlabel(binaryImage);
props = regionprops(labeledImage, 'BoundingBox');
bbox = props.BoundingBox
croppedImageRGB = imcrop(rgbImage, bbox);
subplot(2, 3, 5);
imshow(croppedImageRGB);
grid on;
title('Cropped RGB Image', 'FontSize', fontSize);
% Gray scale version of cropped image
croppedImageGray = imcrop(grayImage, bbox);
subplot(2, 3, 6);
imshow(croppedImageGray);
grid on;
title('Cropped Gray Scale Image', 'FontSize', fontSize);

Best Answer

Related Solutions

MATLAB: How to draw a circle on existed circle ? How to calculate the image shift in pixels from its center

MATLAB: Crop dark area and display the face only

Related Question