How to push a first whites (which is not equal to 0) elements from the mask image into the vector array to make line over stored points.

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kanika bhalla 2021-6-17

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/858385-how-to-push-a-first-whites-which-is-not-equal-to-0-elements-from-the-mask-image-into-the-vector-ar

评论： kanika bhalla 2021-6-18

I have scanned my image horizontally and vertically store the first white elements to a vector. And I want to create a vector which will store the first white elements. After storing the points draw line (as shown in the attached figure) over it.

I have already writen a code in C++, but I don't know how to write it in Matlab.

Here I attach a mask image from where i want to extract the while pixels (First white). For clarifications I have pointed out- what does first whites means in the mask image. Any help is much appreciated to achieve my target.

Hope this is clear.

// C++ code with openCV is shown below:
std::vector<int> firstWhite; // std::vector is a sequence container that encapsulates dynamic size arrays
    for(int i=0; i<80; i++)
    {
        for(int j=0; j<img.rows; j++)
        {
            if(mask.at<uchar>(cv::Point(i,j)) != 0)
            {
                firstWhite.push_back(j);
                j = 10000;    //  for example I have 10000 points in the mask image. I need quite fast access to every point.It is much more efficient to allocate too much memory than letting an array grow.
            }
        }
    }
    cv::line(img,cv::Point(0,firstWhite[0]),cv::Point(79,firstWhite[79]),cv::Scalar(0,0,0),2 );
    
// Converting C++ code to matlab. Below is my trial attemp. But unable to achieve the task.
[columns, rows, plane]=size(maskimage);
firstWhite=[]
for i=1: 80
    for j=1:rows
    if not(maskimage(i,j)==0)
        firstWhite(end+1)=j
    end
    end
end

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KSSV 2021-6-17

在 MATLAB Online 中打开

Attach the original image.

You can get white pixels using:

I = imread('image.png') ; 
I = imcrop(I) ;   % pick only the required part of image 
I1 = rgb2gray(I) ; 
I2 = imbinarize(I1) ; 
[y,x] = find(I2) ; 
imshow(I)
hold on
plot(x,y,'.r')

kanika bhalla 2021-6-17

Thank you so much for your reply @KSSV.

But I want to extract only first whites from the image (as showed in the image for reference). I had tried this [y,x] = find(I2); earlier. This is returning all whites present in the image.

As my task is to draw line over an image. Therefore, I am focused on finding first whites instead of all whites. Another constraint is that all process should be automatic. All process should be automatic. Even I tried in C++ but I don't know how to achieve that task in matlab. I have also attached the code in this post.

Can you please further guide me on this.

Here I attach an original image for your reference.

Many thanks for your help!!

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Answer 1

Walter Roberson 2021-6-17

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/858385-how-to-push-a-first-whites-which-is-not-equal-to-0-elements-from-the-mask-image-into-the-vector-ar#answer_726825

在 MATLAB Online 中打开

iminarize(), bwareafilt()

After that if your binary image is BW, then

first_white_row_idx = sum(cumprod(~BW,1)) + 1

but be careful: rows that have no white at all will show up with output one more than the number of rows

The code above is a vectorized way of find() of the first non-zero pixel for each column. Black is turned to 1's, cumprod that so that the leading 1's on a column are kept but the first 0 stops the run, sum; that gives you the number of 1's before the first 0, which is by construction the number of black pixels before the first white pixel. Add 1 to get the index of the first white pixel.

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kanika bhalla 2021-6-18

编辑：kanika bhalla 2021-6-18

在 MATLAB Online 中打开

Mathworks community is outstanding platform of science and you are leader @Walter Roberson. Thank you so much for dedicating your precious time to help me in my research. I am really thankful to you.

However, I tried to run above code but its giving an error. Here I am attaching slightly modified code. Please help me to achieve my target of drawing line over the first whites.

I have also attached a original, mask, and error image for your reference.

Input_Originalimage = imread('Original_Defectimage'); % Step 1: give original image as an input
Crop_image = imcrop(Input_Originalimage,[360 270 306 185]); % Step 2: Crop the original image
[height, width, plane] = size(Crop_image);
R= Crop_image(:,:,1) % take the red channel of Crop_image
G=Crop_image(:,:,2) % take the green channel of Crop_image
B=Crop_image(:,:,3) % take the blue channel of Crop_image
mask = zeros(height,width); % to create mask image
for i = 1:height
    for j = 1:width
        
      if R(i,j)> 130 & R(i,j) < 150 & G(i,j) > 150 & G(i,j) < 180 & B(i,j) > 110 & B(i,j) < 150
  
          mask(i,j) = 255;    % store 255 pixel values                                                                                                                                                                                          
      end 
      end  
 end
figure; imshow(mask); % this is how I calculated a mask image
% Below is slightly modified code given by you to draw lines over first
% whites
[columns, rows, plane]=size(mask);
idx_offset = 1;   %MATLAB indices start from 1
%std::vector<int> firstWhite; // std::vector is a sequence container that encapsulates dynamic size arrays
firstWhite = zeros(1, 0, 'int32');
%    for(int i=0; i<80; i++)
for i = int32(1) : int32(80)
%    {
%        for(int j=0; j<img.rows; j++)
   for j = int32(0) : int32(rows)
%        {
%            if(mask.at<uchar>(cv::Point(i,j)) != 0)
          if C1(i_idx_offset,j+idx_offset)
%            {
%                firstWhite.push_back(j);
             firstWhite(end+1) = j;
%                j = 10000;    //  for example I have 10000 points in the mask image. I need quite fast access to every point.It is much more efficient to allocate too much memory than letting an array grow.
%            }
             break;
          end
%        }
%    }
   end
end
%    cv::line(img,cv::Point(0,firstWhite[0]),cv::Point(79,firstWhite[79]),cv::Scalar(0,0,0),2 );
    
 hold on
 plot([0, 79], firstWhite([0,79]+idx_offset), 'k', 'linewidth', 2);

Walter Roberson 2021-6-18

在 MATLAB Online 中打开

filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/656085/image.jpeg';

Input_Originalimage = imread(filename); % Step 1: give original image as an input

Crop_image = imcrop(Input_Originalimage,[360 270 306 185]); % Step 2: Crop the original image

imshow(Crop_image)

[height, width, plane] = size(Crop_image);

R= Crop_image(:,:,1); % take the red channel of Crop_image

G=Crop_image(:,:,2); % take the green channel of Crop_image

B=Crop_image(:,:,3); % take the blue channel of Crop_image

mask = R > 130 & R < 150 & G > 150 & G < 180 & B > 110 & B < 150;

mask = bwareafilt(mask, [50 inf]);

figure; imshow(mask); % this is how I calculated a mask image

firstWhite = zeros(1,width);

for col = 1 : width

fw = find(mask(:,col),1);

if isempty(fw)

firstWhite(col) = nan;

else

firstWhite(col) = fw;

end

hold on

plot(firstWhite, 'y', 'linewidth', 2);

figure;

dfw = diff(firstWhite);

plot(dfw)

title('difference in firstWhite')

left_edge_x = find(dfw > 3, 1);

left_edge_y = firstWhite(left_edge_x);

right_edge_x = find(dfw < -3, 1, 'last')+1;

right_edge_y = firstWhite(right_edge_x);

figure

imshow(mask)

hold on

plot(firstWhite, 'y', 'linewidth', 2);

plot([left_edge_x, right_edge_x], [left_edge_y, right_edge_y], 'color', [1 .5 0], 'linewidth', 2)

kanika bhalla 2021-6-18

I am indebted to your kindness and knowledge. I don't know of I'll ever be able to repay you properly. I am forever grateful to you Sir @Walter Roberson.

Next task is to find the first whites from the bottom to draw a line. I am trying best to implement the same according to your provided knowledge and solutions.

Thank you so much for your valuable time and support.

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How to push a first whites (which is not equal to 0) elements from the mask image into the vector array to make line over stored points.

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How to push a first whites (which is not equal to 0) elements from the mask image into the vector array to make line over stored points.

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