How to extract specific edges from an image?

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Harshan Desu 2020-5-6

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https://ww2.mathworks.cn/matlabcentral/answers/523335-how-to-extract-specific-edges-from-an-image

评论： Harshan Desu 2020-7-14

Hello eveyone, I have an image of a car door from which I have to find generate a trajectory from specific edges of the car door. Let me expain the detail about my project.

Project: Finding the edges of a door and used those edges as a trajectory for a sensor that checks edges for Gap/Flush.

Principle: I used Savitzky Golay, Edge Linking and Line Segment Fitting (https://www.peterkovesi.com/matlabfns/#step2line).

Method I used: Image Analyst's Savitzky filter smoothening at three diffrent thresholds, obtain three images and blend them. The output is again processed to Edge linking and line segmenting program.

After all this I am not able to get good edges, its either not smooth or has a lot of unnecessary edges. But the main problem is I am getting a lot of unnecessary edges in the image. To get a Trajectory I need only Three specific edges which I have marked by hand below in red.

Questions:

How to remove unnecessary edges out of the image. Please suggest me a way to get only those three edges? (without manual intervention)
How to smoothening those edges and join them so that i can use it as trajectory for another program?

I have attached the images of input and output. Sorry for the long question.

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Answer 1

Image Analyst 2020-5-7

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https://ww2.mathworks.cn/matlabcentral/answers/523335-how-to-extract-specific-edges-from-an-image#answer_430989

If you have an edge image with a bunch of edges but want edges from only certain locations, you maybe best off using a mask/template to erase everything outside the areas you want to look in.

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Harshan Desu 2020-5-13

在 MATLAB Online 中打开

Hello Sir, thanks for your support. Your answers and programs have been very useful for me as a beginner.

I used a template/mask to erase everything else and obtained the edges I needed.

Now how do I extract edges and curve fit to get a function so that I get the Trajectory of the above curve. This is my code..

    im = imread('blend2_21_OPPFS.png');
    im = rgb2gray(im);
    props = regionprops(im, 'Area');
    %im = imread('pout.tif');        % data
% smooth the image
clc;
clear;
close all;
% Read Input Image
InputImage=imread('blend2_22_OPPFS.png');
%Resize the Image
%InputImage=imresize(InputImage,[256 256]);
% Display the Image
imshow(InputImage);
% Get Inputs from Mouse,Select 4 Seed Points in Image
[Col Row]=ginput(6);
c =Col;
r =Row;
%c = [352.313364055300;100.645161290323;119.571428571429;132.870967741936;353.847926267281;353.847926267281];
%r = [111.244239631336;82.5990783410139;140.912442396313;181.322580645161;188.483870967742;187.460829493088];
% Select polygonal region of interest
BinaryMask = roipoly(InputImage,c,r);
figure, imshow(BinaryMask);title('Selected Region of Interest');
%Create Buffer for ROI
ROI=zeros(333,476);
%Create Buffer for NONROI
NONROI=zeros(33,467);
for i=1:333
for j=1:476
if BinaryMask(i,j)==1
ROI(i,j)=InputImage(i,j);
else
NONROI(i,j)=InputImage(i,j);
end
end
end
%Display ROI and Non ROI
figure;
subplot(1,2,1);imshow(ROI,[]);title('ROI');
subplot(1,2,2);imshow(NONROI,[]);title('NON ROI');

Image Analyst 2020-7-9

Try a threshold that gets all the edges then use bwselect() to manually pick out the one you want.

Harshan Desu 2020-7-14

The enitre process has to have no manual interverntion. Thanks for the Idea anyways!

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