MATLAB: How to calculate the area of this crescent shape

scrollspiral

Hi all,

I am trying to calculate the area of this crescent shape attached in the image here. My attempt was to use the polyarea function in matlab to compute the area for the outer and inner coils and subtract them. Is this correct? Please provide your inputs. If any better alternates are available, kindly suggest.

Thanks Arun

Best Answer

Here are three different ways of getting an area. The areas are different because of the different ways they define area. What's your definition?

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 = 20;
[grayImage, map] = imread('crescent.gif');
subplot(2,1,1);
imshow(grayImage, []);
colormap(map);
colorbar;
axis on;
title('Original GIF', 'fontSize', fontSize);
binaryImage = grayImage == 1;
binaryImage = imclearborder(binaryImage);
subplot(2,1,2);
imshow(binaryImage);
title('Binary Image', 'fontSize', fontSize);
% Measure the area from bwarea
baArea = bwarea(binaryImage)
% Measure the area via regionprops
measurements = regionprops(bwlabel(binaryImage), 'Area');
rpArea = measurements.Area
% Measure the area via polyarea
boundaries = bwboundaries(binaryImage);
x = boundaries{1}(:, 2);
y = boundaries{1}(:, 1);
pArea = polyarea(x, y)
message = sprintf('The area from bwarea() = %.2f\nThe area from regionprops = %.2f\nThe area from polyarea() = %.2f', ...
  baArea, rpArea, pArea);
fprintf('%s\n', message);
uiwait(helpdlg(message));

Results in command window:

The area from bwarea() = 41475.63
The area from regionprops = 41418.00
The area from polyarea() = 40801.50

Related Solutions

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);

MATLAB: Calculating the area inside boundary

Use polyarea:

area = polyarea(xCoordinates, yCoordinates);

Best Answer

Related Solutions

MATLAB: Crop dark area and display the face only

MATLAB: Calculating the area inside boundary

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