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How to remove unwanted portion from background?

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Ostu's thresholding method is good and easy. For some images it clearly idetified the object in interest, but some other images it lefts some unwanted portion. When dealing with more 1000 images running in batch and applying ostu's method is not giving any good outputs. How can I improve this algorithms or any other idea where after applying ostu's methods we can remove unwanted portion and that will applicable for all images.

Answers (5)

Image Analyst
Image Analyst on 18 Oct 2021
It often does not work well for images that do not have a nice well separated bimodal histogram. The triangle method works well for skewed histograms, like with a log-normal shape. I'm attaching my implementation.
imbinarize() has an 'adaptive' option that might work well for you.
  7 Comments
Zara Khan
Zara Khan on 18 Aug 2022
Thank you sir for the links. Still I want a help. How can we use any deep learning method in segmenting these hand gestures attached above??
Image Analyst
Image Analyst on 18 Aug 2022
@Zara Khan I don't know. I haven't done it. If none of the papers links I gave you uses that particular method (deep learning) and you don't want to use any of the successful methods that they developed, used and published, then you're on your own. I'm no further along than you are, and I don't plan on going into gesture research so don't wait on me.

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yanqi liu
yanqi liu on 26 Oct 2021
sir,may be upload some image samples to develop
  1 Comment
Zara Khan
Zara Khan on 26 Oct 2021
Uploaded few images . Please see in Image Analyst's reply section. Thanks.

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yanqi liu
yanqi liu on 27 Oct 2021
sir,please check the follow code to get some information
clc; clear all; close all
urls={'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779463/img16.png',...
'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779458/img6.png',...
'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779453/img4.png',...
'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779448/img2.png',...
'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779443/img1.png',...
'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779438/img1%20(2).png'};
for k = 1 : length(urls)
im = imread(urls{k});
if ndims(im) == 3
im = rgb2gray(im);
end
im2 = imadjust(im,stretchlim(im),[]);
bw = imbinarize(im2,'adaptive','ForegroundPolarity','dark','Sensitivity',0.85);
bw = bwareaopen(bw, 100);
bw = imopen(bw, strel('line', 9, 90));
bw = imclose(bw, strel('line', 15, 0));
bw = imfill(bw, 'holes');
bw = bwareaopen(bw, 500);
[L,num] = bwlabel(bw);
vs = [];
for i = 1 : num
bwi = bw;
bwi(L~=i) = 0;
vi = mean(double(im2(logical(bwi))));
vs(i) = vi;
end
[~,ind] = max(vs);
bw(L~=ind) = 0;
[r,c] = find(logical(bw));
rect = [min(c) min(r) max(c)-min(c) max(r)-min(r)];
figure; imshow(im, []);
hold on; rectangle('Position', rect, 'EdgeColor', 'r', 'LineWidth', 2, 'LineStyle', '-');
end
  6 Comments
Image Analyst
Image Analyst on 20 Aug 2022
OK well that's what happens if people don't comment their code. What find does is to find non-zero (white) pixel locations and put their row and column coordinates into variables r and c.
Then by using min and max she assumes that there is just one blob so the min and max will give you the left column, right column, top row, and bottom row. Now to use the rectangle function you need to pass it a position array in the form [xLeft, yTop, width, height] so those are the 4 expressions she put into this line of code:
rect = [min(c) min(r) max(c)-min(c) max(r)-min(r)];
Now you can pass that in for the 'Position' argument to the rectangle() function like this:
rectangle('Position', rect, 'EdgeColor', 'r', 'LineWidth', 2, 'LineStyle', '-');
Zara Khan
Zara Khan on 21 Aug 2022
Edited: Zara Khan on 21 Aug 2022
@Image Analyst Thank you sir. But this method is not adaptive. Somehow working well for these attached images but when working 1320 images in batch the rectangle I am getting outside the image object means in background for some images. how to overcome this? Even I am not getting why these many filters are being used befire drawing the recctangles
[L,num] = bwlabel(bw);
vs = [];
for i = 1 : num
bwi = bw;
bwi(L~=i) = 0;
vi = mean(double(im2(logical(bwi))));
vs(i) = vi;
end
[~,ind] = max(vs);
bw(L~=ind) = 0;

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yanqi liu
yanqi liu on 27 Oct 2021
sir,use some basic method may be not the best choice,so may be consider some DeepLearning method,such as unet
clc; clear all; close all
urls={'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779463/img16.png',...
'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779458/img6.png',...
'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779453/img4.png',...
'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779448/img2.png',...
'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779443/img1.png',...
'https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/779438/img1%20(2).png'};
for k = 1 : length(urls)
im = imread(urls{k});
if ndims(im) == 3
im = rgb2gray(im);
end
im2 = imadjust(im,stretchlim(im),[]);
bw = imbinarize(im2,'adaptive','ForegroundPolarity','dark','Sensitivity',0.85);
bw = bwareaopen(bw, 100);
bw = imopen(bw, strel('line', 9, 90));
bw = imclose(bw, strel('line', 12, 0));
bw = imfill(bw, 'holes');
bw = bwareaopen(bw, 500);
[L,num] = bwlabel(bw);
vs = [];
for i = 1 : num
bwi = bw;
bwi(L~=i) = 0;
vi = mean(double(im2(logical(bwi))));
vs(i) = vi;
end
[~,ind] = max(vs);
bw(L~=ind) = 0;
bw = logical(bw);
bw = imfill(bw, 'holes');
bw = imclose(bw, strel('disk', 15));
[r,c] = find(logical(bw));
rect = [min(c) min(r) max(c)-min(c) max(r)-min(r)];
im2 = im;
im2(~bw) = 0;
figure; imshow(im2, []);
%hold on; rectangle('Position', rect, 'EdgeColor', 'r', 'LineWidth', 2, 'LineStyle', '-');
end
  16 Comments
Image Analyst
Image Analyst on 23 Aug 2022
bw = imopen(bw, strel('line', 9, 90));
bw = imclose(bw, strel('line', 12, 0));
It would have been good if she had commented all the lines of code especially since the algorithm is long and fairly complicated. She's using line because she wanted to filter preferentially along a certain direction rather than isotropically in all directions. The imopen will get rid of tendrils that are vertical and less than 9 pixels wide. The imclose will fill in gaps along horizontal edges of the blob.

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Zara Khan
Zara Khan on 27 Aug 2022
clc; clear all; close all
im=imread('https://in.mathworks.com/matlabcentral/answers/uploaded_files/1109360/img_4.png');
im2 = imadjust(im,stretchlim(im),[]);
bw = imbinarize(im2,'adaptive','ForegroundPolarity','dark','Sensitivity',0.85);
bw = bwareaopen(bw, 100);
bw = imopen(bw, strel('line', 9, 90));
bw = imclose(bw, strel('line', 15, 0));
bw = imfill(bw, 'holes');
bw = bwareaopen(bw, 500);
[L,num] = bwlabel(bw);
vs = [];
for i = 1 : num
bwi = bw;
bwi(L~=i) = 0;
vi = mean(double(im2(logical(bwi))));
vs(i) = vi;
end
[~,ind] = max(vs);
bw(L~=ind) = 0;
[r,c] = find(logical(bw));
rect = [min(c) min(r) max(c)-min(c) max(r)-min(r)];
figure; imshow(im, []);
hold on; rectangle('Position', rect, 'EdgeColor', 'r', 'LineWidth', 2, 'LineStyle', '-');
@Image Analyst @yanqi liu sir this algorithm not able to segement this gesture
  1 Comment
Image Analyst
Image Analyst on 27 Aug 2022
I am not a gesture recognition researcher. But I know that any successful algorithm will not just be one page of code. You need to use a robust algorithm already developed by specialists in the area who have published their algorithms. Go here to see a list of them:

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