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

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Tayyaba Bano
Tayyaba Bano 2020 年 11 月 26 日
コメント済み: Tayyaba Bano 2021 年 8 月 30 日
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
  2 件のコメント
KALYAN ACHARJYA
KALYAN ACHARJYA 2020 年 11 月 26 日
"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
Tayyaba Bano 2020 年 11 月 26 日
Thanks.
I hope its attached now.

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回答 (4 件)

KALYAN ACHARJYA
KALYAN ACHARJYA 2020 年 11 月 26 日
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
  2 件のコメント
Tayyaba Bano
Tayyaba Bano 2020 年 11 月 27 日
Thanks :)
KALYAN ACHARJYA
KALYAN ACHARJYA 2020 年 11 月 27 日
編集済み: KALYAN ACHARJYA 2020 年 11 月 27 日
To get the indices of boundary, apply hit and miss transformation, the
[r,c]=find(resultant_image==1)

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Image Analyst
Image Analyst 2020 年 11 月 26 日
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;
  2 件のコメント
Tayyaba Bano
Tayyaba Bano 2020 年 11 月 27 日
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
Image Analyst 2020 年 11 月 27 日
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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Image Analyst
Image Analyst 2020 年 11 月 27 日
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');
  15 件のコメント
Tayyaba Bano
Tayyaba Bano 2020 年 12 月 18 日
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
Image Analyst 2020 年 12 月 18 日
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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Tayyaba Bano
Tayyaba Bano 2021 年 8 月 30 日
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
  3 件のコメント
Tayyaba Bano
Tayyaba Bano 2021 年 8 月 30 日
Im really sorry for that.
I want to ask:
  1. How to avoid blur edges in the averaged image?
  2. How to extract the boundary from that average image?
Thanks
Tayyaba Bano
Tayyaba Bano
Tayyaba Bano 2021 年 8 月 30 日
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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