How to trace the boundray of object in an image using MATLAB?

Question

Tayyaba Bano 2020-11-26

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评论： Tayyaba Bano 2021-8-30

Hi,

I want to trace the boundary of an object in an image.(the bended black part)

I am attaching the binarised image herewith.

My questions are:

when I use dim= size(I) inin the following code, it gives different size and when I type in dim = size(BW), it gives different pixel size, so which should I follow?

I = imread('flap2.png');

imshow(I);

dim = size(I)

secondly how can I define the row and coloumn using this size information in order to continue with bwtraceboundary , because when i use this command it gives me a following error:

Error using bwtraceboundary

Expected input number 1, BW, to be two-dimensional.

waiting for a kind response.

Regards

Tayyaba

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KALYAN ACHARJYA 2020-11-26

"I want to trace the boundary of an object in an image.(the bended black part)"

Which image? Can you attach it (Please use clip button)

Tayyaba Bano 2020-11-26

Image BW.jpg

Thanks.

I hope its attached now.

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Answer 1

KALYAN ACHARJYA 2020-11-26

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在 MATLAB Online 中打开

se=strel('disk',2);
im=imerode(~binary_image,se);
result=bwareafilt(im,1);
result=imdilate(result,se);
imshow(result);

Please adjust the morpho operation to get more accurate results

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Tayyaba Bano 2020-11-27

Thanks :)

KALYAN ACHARJYA 2020-11-27

编辑：KALYAN ACHARJYA 2020-11-27

在 MATLAB Online 中打开

To get the indices of boundary, apply hit and miss transformation, the

[r,c]=find(resultant_image==1)

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Answer 2

Image Analyst 2020-11-26

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在 MATLAB Online 中打开

If you want to manually trace some boundary. Use drawfreehand().

If you have a binary image and you want an image of the perimeter only, then use bwperim().

perimImage = bwperim(binaryImage);
imshow(perimImage);

If you have a binary image and you want a list of the (x,y) coordinates, use bwboundaries().

boundaries = bwboundaries(binaryImage);
hold on; % Don't let boundaries blow away the image.
for k = 1 : length(boundaries)
    thisBoundary =  boundaries{k};
    x = thisBoundary(:, 2);
    y = thisBoundary(:, 1);
    plot(x, y, 'LineWidth', 2);
end
hold off;

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Tayyaba Bano 2020-11-27

Thank you very much for your kind reply,

Yes I actually need the (x,y) coordinates of the boundary in the binary image.

I tried this command already but it states the following error:

Error using bwboundaries

Expected input number 1, BW, to be two-dimensional.

Error in bwboundaries>parseInputs (line 187)

validateattributes(BW_in, {'numeric','logical'}, {'real','2d','nonsparse'}, ...

Error in bwboundaries (line 140)

[BW, conn, findHoles] = parseInputs(args{:});

Error in Untitled3 (line 4)

boundaries = bwboundaries(BW);

Alltough the image is two-dimensional, still it displays this error.

Couldyou please help me in this regards

Thanks much.

Tayyaba

Image Analyst 2020-11-27

You passed in your color image. You need to use the binary image, after it's been converted to gray scale and segmented.

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Answer 3

Image Analyst 2020-11-27

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在 MATLAB Online 中打开

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 = 22;
%--------------------------------------------------------------------------------------------------------
%    READ IN IMAGE
folder = pwd;
baseFileName = 'image.jpeg';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
	% The file doesn't exist -- didn't find it there in that folder.
	% Check the entire search path (other folders) for the file by stripping off the folder.
	fullFileNameOnSearchPath = baseFileName; % No path this time.
	if ~exist(fullFileNameOnSearchPath, '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.
% 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, 3, 1);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize, 'Interpreter', 'None');
impixelinfo;
hFig = gcf;
hFig.WindowState = 'maximized'; % May not work in earlier versions of MATLAB.
drawnow;
% The image has a huge white frame around it.  Let's crop that away.
verticalProfile = all(grayImage == 255, 2);
row1 = find(~verticalProfile, 1, 'first');
row2 = find(~verticalProfile, 1, 'last');
horizontalProfile = all(grayImage == 255, 1);
col1 = find(~horizontalProfile, 1, 'first');
col2 = find(~horizontalProfile, 1, 'last');
% Do the crop
grayImage = grayImage(row1:row2, col1:col2);
% Display the image.
subplot(2, 3, 2);
imshow(grayImage, []);
axis('on', 'image');
title('Cropped Grayscale Image', 'FontSize', fontSize, 'Interpreter', 'None');
impixelinfo;
% Update size.
[rows, columns, numberOfColorChannels] = size(grayImage);
% Display histogram
subplot(2, 3, 3);
imhist(grayImage);
grid on;
title('Histogram of gray image', 'FontSize', fontSize);
%--------------------------------------------------------------------------------------------------------
%    SEGMENTATION OF IMAGE
% Get a binary image
mask = grayImage < 25;  %imbinarize(grayImage);
% Display the mask.
subplot(2, 3, 4);
imshow(mask, []);
impixelinfo;
title('Initial Binary Image', 'FontSize', fontSize, 'Interpreter', 'None');
impixelinfo;
% Make a circle mask to get rid of corners
% Create a logical image of a circle with specified
% diameter, center, and image size.
% First create the image.
imageSizeX = columns;
imageSizeY = rows;
[columnsInImage, rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
centerX = columns/2;
centerY = rows/2;
radius = 450;
circlePixels = (rowsInImage - centerY).^2 ...
    + (columnsInImage - centerX).^2 <= radius.^2;
% circlePixels is a 2D "logical" array.
% Now, display it.
% imshow(circlePixels) ;
% title('Binary image of a circle');
% Erase the corners
mask = mask & circlePixels;
% Do an opening to break the stick away from the background things.
se = strel('disk', 2, 0);
mask = imopen(mask, se);
% Take the biggest blob.
mask = bwareafilt(mask, 1);
% Fill holes
mask = imfill(mask, 'holes');
% Blur it a bit to smooth it out.
windowSize = 17;
kernel = ones(windowSize, windowSize) / windowSize ^ 2;
mask = imfilter(mask, kernel) > 0.5;
subplot(2, 3, 5);
imshow(mask, []);
impixelinfo;
title('Final Binary Image', 'FontSize', fontSize, 'Interpreter', 'None');
impixelinfo;
% Get boundaries and plot them, just for fun.
boundaries = bwboundaries(mask);
subplot(2, 3, 6);
imshow(grayImage); % Show cropped image again.
hold on;
for k = 1 : length(boundaries)
	thisBoundary = boundaries{k};
	x = thisBoundary(:, 2);
	y = thisBoundary(:, 1);
	plot(x, y, 'r-', 'LineWidth', 2);
end
title('Image With Boundaries', 'FontSize', fontSize, 'Interpreter', 'None');

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Tayyaba Bano 2020-12-2

在 MATLAB Online 中打开

Fig.png

Thank you very much for your reply.

I used the following code for the cropped image as attached. And the objective is to get the boundary across the one end only as shown last time.

grayImage = imread('flap2.tif');
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
	grayImage = rgb2gray(grayImage);
	
end
% Display the image.
subplot(2, 3, 1);
imshow(grayImage, []);
title('Original Grayscale Image');
impixelinfo;
%--------------------------------------------------------------------------------------------------------
%    SEGMENTATION OF IMAGE
% Get a binary image
mask = grayImage < 25;  %imbinarize(grayImage);
% Display the mask.
subplot(2, 3, 4);
imshow(mask, []);
impixelinfo;
title('Initial Binary Image');
impixelinfo;
% Get boundaries and plot them.
boundaries = bwboundaries(mask);
subplot(2, 3, 6);
hold on;
for k = 1 : length(boundaries)
	thisBoundary = boundaries{k};
	x = thisBoundary(:, 2);
	y = thisBoundary(:, 1);
	plot(x, y, 'r-', 'LineWidth', 2);
end

Tayyaba Bano 2020-12-4

在 MATLAB Online 中打开

untitled.fig

I used that too but I got the same results, as I have attached previously,

it is giving the edge in the middle I guess and it is also still not clear.

may be i have to change the threshold for mask, instead of 25.

im attaching it again. and code is as follows:

grayImage = imread('flap2.tif');
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
	grayImage = rgb2gray(grayImage);
	
end
% Display the image.
subplot(2, 3, 1);
imshow(grayImage, []);
title('Original Grayscale Image');
impixelinfo;
%--------------------------------------------------------------------------------------------------------
%    SEGMENTATION OF IMAGE
% Get a binary image
mask = grayImage < 25;  %imbinarize(grayImage);
% Display the mask.
subplot(2, 3, 4);
imshow(mask, []);
impixelinfo;
title('Initial Binary Image');
impixelinfo;
% Get boundaries and plot them.
boundaries = bwboundaries(mask);
subplot(2, 3, 6);
hold on;
for k = 1 : length(boundaries)
	thisBoundary = boundaries{k};
	x = thisBoundary(:, 2);
	y = thisBoundary(:, 1);
	plot(x, y, 'r-', 'LineWidth', 2);
end
title('Image With Boundaries');
lastRow = zeros(1, columns);
for col = 1 : columns
    r = find(mask(:, col), 1, 'last');
    if ~isempty(r)
        % There is at least one white pixel in this column.
        lastRow(col) = r;
    end
end

Tayyaba Bano 2020-12-18

Thank you very much for your detailed reply.

Actually I have to apply the code for number of images. Initially it worked well but for 401 and some others it doesnot show the compelete boundary.

Any how I am trying further to improve it.

Regards

Tayyaba

Image Analyst 2020-12-18

Can you increase your exposure time to get a less noisy photo?

Maybe try some denoising routines, of which there are many. Maybe imnlmfit().

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Answer 4

Tayyaba Bano 2021-8-30

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在 MATLAB Online 中打开

Hi,

I have averaged 100 images and I have to get the boundary of that average image.

I run the following code for getting boundaries:

grayImage = imread('100.tif');
[rows, columns, numberOfColorChannels] = size(grayImage);
if numberOfColorChannels > 1
	grayImage = rgb2gray(grayImage);
	
end
% Display the image.
subplot(2, 3, 1);
imshow(grayImage, []);
title('Original Grayscale Image');
impixelinfo;
% Croping image.
grayImage = imcrop(grayImage);
% Display the image.
subplot(2, 3, 2);
imshow(grayImage, []);
axis('on', 'image');
title('Cropped Grayscale Image');
impixelinfo;
% Update size.
[rows, columns, numberOfColorChannels] = size(grayImage);
% Display histogram
subplot(2, 3, 3);
imhist(grayImage);
grid on;
title('Histogram of gray image');
%--------------------------------------------------------------------------------------------------------
%    SEGMENTATION OF IMAGE
% Get a binary image
mask = grayImage < 39

;  %imbinarize(grayImage);
% Display the mask.
subplot(2, 3, 4);
imshow(mask, []);
impixelinfo;
title('Initial Binary Image');
impixelinfo;
% Make a circle mask to get rid of corners
% Create a logical image of a circle with specified
% diameter, center, and image size.
% First create the image.
imageSizeX = columns;
imageSizeY = rows;
[columnsInImage, rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
centerX = columns/2;
centerY = rows/2;
% radius = max(centerX, centerY);
radius = 500;
circlePixels = (rowsInImage - centerY).^2 ...
    + (columnsInImage - centerX).^2 <= radius.^2;
% circlePixels is a 2D "logical" array.
% Now, display it.
% imshow(circlePixels) ;
% title('Binary image of a circle');
% Erase the corners
mask = mask & circlePixels;
% Fill interior holes.
mask = imfill(mask, 'holes');
% Check areas so we know what the size of the small specks are so we can filter them out.
props = regionprops(mask, 'Area');
allAreas = sort([props.Area], 'ascend')
% Get rid of blobs smaller than 300 in size
mask = bwareaopen(mask, 300);
subplot(2, 3, 5);
imshow(mask, []);
impixelinfo;
title('Final Binary Image');
impixelinfo;
% Get boundaries .
boundaries = bwboundaries(mask);
subplot(2, 3, 6);
imshow(grayImage); 
hold on;
for k = 1 : length(boundaries)
	thisBoundary = boundaries{k};
	x = thisBoundary(:, 2);
	y = thisBoundary(:, 1);
	plot(x, y, 'r-', 'LineWidth', 2);
end
title('Image With Boundaries')

The average image is blur and also because of this the boundaries are not clear. I run the following code for taking average:

I0 = imread('img_1.tif')
sumImage = double(I0); % Inialize to first image.
for i=2:100 
  rgbImage = imread(['img_',num2str(i),'.tif']);
  sumImage = sumImage + double(rgbImage);
end;
meanImage = sumImage / 100;
imshow(meanImage(:), []);title('Average');
imshow(uint8(meanImage));

The original averaged image and the result of the boundary

code are attached herewith.

Thanks and waiting for your kind response.

Regards

Tayyaba Bano

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Tayyaba Bano 2021-8-30

Im really sorry for that.

I want to ask:

How to avoid blur edges in the averaged image?
How to extract the boundary from that average image?

Thanks

Tayyaba Bano

Tayyaba Bano 2021-8-30

img_1.png

Another point I have noticed that, the difference in the scale for averaged images and the scale beforetaking the average.

For example the scale of averaged image is ranging from 0-450 whereas the scale before taking the average is 0-1400.

I attached the cropped image before taking the average.

Why the difference in scale with average?

Kind regards

Tayyaba Bano

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How to trace the boundray of object in an image using MATLAB?

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