How to reduce blob using aspect ratio?
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![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/166103/image.png)
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I have a binary image with 4 blobs. 3 of them has an aspect ratio of more than 1. and 1 has aspect ratio of 1. Now I want to reduce that blobs which aspect ratio more than 1 in binary image. How could i do this. Can some one please provide a code??
A picture is provided for understanding.
2 个评论
采纳的回答
Image Analyst
2017-7-19
Dominic, here is the full demo:
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 = 25;
%===============================================================================
% Get the name of the image the user wants to use.
baseFileName = '4.png';
% Get the full filename, with path prepended.
folder = []; % Determine where demo folder is (works with all versions).
fullFileName = fullfile(folder, baseFileName);
%===============================================================================
% Read in a demo image.
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, 1, 1);
imshow(grayImage, []);
axis on;
axis image;
caption = sprintf('Original Gray Scale Image');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo();
% 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;
% Threshold the image.
binaryImage = grayImage > 128;
% Find connected components (blobs).
labeledImage = bwlabel(binaryImage);
% Make the measurements of the bounding boxes.
props = regionprops(labeledImage, 'BoundingBox');
bb = [props.BoundingBox];
allWidths = bb(3:4:end)
allHeights = bb(4:4:end)
aspectRatio = [allWidths./allHeights ; allHeights ./ allWidths]
aspectRatios = max(aspectRatio, [], 1)
compactIndexes = find(aspectRatios > 1.5) % or whatever.
% Extract only those blobs with high aspect ratios.
binaryImage = ismember(labeledImage, compactIndexes);
% Display the image.
subplot(2, 1, 2);
imshow(binaryImage, []);
axis on;
axis image;
caption = sprintf('Final binary image with only high aspect ratio blobs');
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/177491/image.png)
3 个评论
Image Analyst
2017-7-19
If you have a fairly recent version of MATLAB, you can filter by that before you even call bwconncomp(), bwlabel() or regionprops(). Just call bwpropfilt() and pass in the min and max values you want to accept.
更多回答(2 个)
Walter Roberson
2017-7-18
If you used regionprops() to get the BoundingBox in order to calculate the aspect ratio, then you can also ask for the pixel ID list. For each region that does not pass your aspect ratio test, assign 0 to the pixels given by those indices.
9 个评论
Walter Roberson
2017-7-18
Change the line to
binary_image(this_roi(2) : this_roi(2) + this_roi(4) - 1, this_roi(1) : this_roi(1) + this_roi(3) - 1) = 0;
Image Analyst
2017-7-18
Use regionprops() to ask for the bounding box. Then compute aspect ratio: width over height, and height over width and take the max (or min), whichever you're using. Then use find() to find out which blobs to keep, then use ismember() to extract only those blobs. See my Image Segmentation Tutorial for a detailed demo. http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862&sort=downloads_desc
2 个评论
Image Analyst
2017-7-18
If I have more time later I'll help more, in the meantime, do this:
props = regionprops(labeledImage, 'BoundingBox');
bb = [props.BoundingBox];
allWidths = bb(3:4:end);
allHeights = bb(4:4:end);
aspectRatio = [allWidths./allHeights ; allHeights ./ allWidths]
aspectRatios = max(aspectRatio, [], 1)
compactIndexes = find(aspectRatios > 5); % or whatever.
binaryImage = ismember(labeledImage, compactIndexes);
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