MATLAB: How to get the inner and outer outlines of a boundary in an image

boundaryImage Processing ToolboxMATLAB

I'm trying to get the inner and outer outlines of the objects in an image to perform ioopl matching according to a paper i'm trying to implement. I want to contract my object boundary inwards and also expand it outward. eg:

how do i do this?

Best Answer

Assuming you have the initial green boundary, you can convert it into a binary image and then use imdilate or imerode to grow or shrink the boundary

mask = poly2mask(x, y, rows, columns);
bigMask = imdilate(mask, true(3));
bigBoundary = bwboundaries(bigMask);
smallMask = imerode(mask, true(3));
smallBoundary = bwboundaries(smallMask);

Change the 3 to some other, larger number if you want to grow or shrink by some different amount.

Related Solutions

MATLAB: I have RGB (MxNx3) image and a binary mask (MxN). I want to place this mask over the RGB such that a line should be shown along the shape of the mask on the RGB image.

Call bwboundaries() then plot

boundaries = bwboundaries(binaryImage);
numberOfBoundaries = size(boundaries, 1);
hold on;
for k = 1 : numberOfBoundaries
  thisBoundary = boundaries{k};
  plot(thisBoundary(:,2), thisBoundary(:,1), 'r-', 'LineWidth', 2);
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: I have RGB (MxNx3) image and a binary mask (MxN). I want to place this mask over the RGB such that a line should be shown along the shape of the mask on the RGB image.

MATLAB: Crop dark area and display the face only

Related Question