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

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?

Answer 1

[Image Analyst]

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.

[charuleelaa vanilavarasu]

what are the parameters in the poly2mask function? as in what is the input for that? i used bwboundaries to get the boundary.

[Image Analyst]

OK, if you used bwboundaries, then you already have a binary image (mask), and so you don't need to use poly2mask to create a mask. Just use the 4 other lines of code on whatever you called your binary image.

[charuleelaa vanilavarasu]

I tried the following:

A = imread('image\2.jpg');

b=rgb2gray(A);

l=graythresh(b);

imshow(A);title('Boundary Extraction');

hold on

BW=im2bw(b,l);

[B,~,~,A] = bwboundaries(BW);

boundaries = bwboundaries(BW);

bigMask = imdilate(BW, true(3));

bigBoundary = bwboundaries(bigMask);

smallMask = imerode(BW, true(3));

smallBoundary = bwboundaries(smallMask);

numberOfBoundaries = size(boundaries);

for k = 1 : numberOfBoundaries

thisBoundary = boundaries{k};

plot(thisBoundary(:,2), thisBoundary(:,1), 'g', 'LineWidth',2);

end

hold on;

numberOfBoundaries = size(bigBoundary);

for k = 1 : numberOfBoundaries

thisBoundary = boundaries{k}; plot(thisBoundary(:,2), thisBoundary(:,1), 'r', 'LineWidth',2);

end

hold on;

numberOfBoundaries = size(smallBoundary);

for k = 1 : numberOfBoundaries

thisBoundary = boundaries{k};

plot(thisBoundary(:,2), thisBoundary(:,1), 'b', 'LineWidth',2);

end

But it doesn't seem to work. I guess im plotting the boundaries wrong? Sorry i have no idea about matlab or image processing. Really new to this.

[Image Analyst]

You forgot to attach 2.jpg. So I don't know what your code is doing. If you're starting with the aerial photo, then I can tell you that that simple thresholding method will not get you the building outlined in green. Maybe you're starting with a binary image of the building already. You seemed to indicate that you had implemented the paper up through the initial green boundary-finding step, and that you only needed the subsequent boundary shrinking and expanding steps. If that's not true, then please clarify exactly what you are starting with, and what you have been able to do so far with the algorithm detailed in the paper.

[charuleelaa vanilavarasu]

I have attached the image. the code i posted was just a trial script i was running to check how it might work. The problem is i have not been able to implement that paper(after several attempts but no luck). But in this particular image using otsu and the grayimage>92 i could get the shadowed area. I thought i could i try and and see how the boundary thing will work on this image.

[Image Analyst]

The code looks like it should work. What goes wrong? Maybe you should use visboundaries() instead of the for loop to do the plotting. I can probably try it later today.

[charuleelaa vanilavarasu]

it doesn't seem to work. Im just getting a image with a blue boundary. i tried increasing the value 3. doesn't do the trick. If you could try it, that would be great thank you.

[Yushuo]

imerode worked

Answer 2

[Image Analyst]

Try this:

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;

% Read in color image.
rgbImage = imread('2.jpg');
% Display the image.
subplot(2, 2, 1);
imshow(rgbImage);
title('RGB Image', 'FontSize', fontSize);

grayImage=rgb2gray(rgbImage);
thresholdLevel=graythresh(grayImage);
% Display the image.
subplot(2, 2, 2);
imshow(grayImage);
title('Gray Scale Image', 'FontSize', fontSize);
% 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', 'Demo by ImageAnalyst', 'NumberTitle', 'Off') 
drawnow;

hold on
binaryImage = im2bw(grayImage,thresholdLevel);
% Invert it and extract the largest blob.
binaryImage = bwareafilt(~binaryImage, 1);
% Fill Holes.
binaryImage = imfill(binaryImage, 'holes');

% Display the image.
subplot(2, 2, 3);
imshow(binaryImage);
title('Binary Image', 'FontSize', fontSize);

% Display the image.
subplot(2, 2, 4);
imshow(rgbImage);
title('RGB Image with 3 outlines', 'FontSize', fontSize);
axis on;
hold on;

[B,~,~,rgbImage] = bwboundaries(binaryImage);
boundaries = bwboundaries(binaryImage);
visboundaries(boundaries, 'Color', 'b');
bigMask = imdilate(binaryImage, true(13));
bigBoundary = bwboundaries(bigMask);
% Display the boundary over the image.
visboundaries(bigBoundary);

smallMask = imerode(binaryImage, true(7));
smallBoundary = bwboundaries(smallMask);
% Display the boundary over the image.
visboundaries(smallBoundary, 'Color', 'm');

[charuleelaa vanilavarasu]

Thanks a ton! But i'm getting these errors: Undefined function 'bwareafilt' for input arguments of type 'double'. If i comment that and run it,Undefined function 'visboundaries' for input arguments of type 'cell'. which visboundaries and which bwareafilt returns not found and its not in my bin folder. what do i do?

[Image Analyst]

You have an old version. Go to the Mathworks site and download the latest version.

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