Is the number of points in a line image equals the number of pixels?

Dear all, Is there any matlab image operator or function that tell the matlab to process an image of line as a group of pixels in such each point in the line is expressed as one pixel? Thanks

[Mohammadreza]

No,

[m,n]=size(image);
number_of_pixels=m*n;

[sali]

Thanks for your reply, to make my question more clear I have the attached image that I use it in my code, I noticed from the results that the matlab deals with each point in any line in the image as two adjacent points while I wanted it to process each point as a single pixel not two adjacent pixels.

[Mohammadreza]

My pleasure sali; I know from your explanation, you need one pixcel of each line width. you can use 'for' loop and select for example first or second pixel of each 2 pixel of line width.

[Image Analyst]

I have no idea what this means "process an image of line as a group of pixels in such each point in the line is expressed as one pixel". Do you want to do area processing of a group of pixels in a sliding window centered over the image pixel, like

img = conv(img, kernel, 'same');

or do you want to do point processing where you just process each pixel by itself as a single pixel, like

img = image * 0.5;

Or do you mean how to skeletonize an image, like

skelImage = bwmorph(binaryImage, 'skel', inf);

Please try to clarify your problem statement so as to not waste our time or yours and get you a speedy solution.

[sali]

Thanks John for your answer I'll try this as well and see. Thanks Image Analyst for the answer , what I meant is reducing the line width to be one pixel before processing.

[Image Analyst]

Then you'll want to use

skelImage = bwmorph(binaryImage, 'skel', inf);

See my answer below for a full demo with your image.

Answer 1

[Image Analyst]

Try this 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 = 20;

%===============================================================================
% Read in gray scale demo image.
folder = pwd; % Determine where demo folder is (works with all versions).
baseFileName = 'image1.png';
% 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
rgbImage = 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(rgbImage)
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(rgbImage);
  % 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 = rgbImage(:, :, 1); % Take red channel.
else
  grayImage = rgbImage; % It's already gray scale.
end
% Now it's gray scale with range of 0 to 255.

% Display the image.
subplot(2, 2, 1);
imshow(grayImage, []);
title('Original Image', 'FontSize', fontSize, 'Interpreter', 'None');
axis('on', 'image');
hp = impixelinfo();

%------------------------------------------------------------------------------
% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0, 0.04, 1, 0.96]);
% 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;

% Binarize the image
binaryImage = grayImage < 128;
% Display the image.
subplot(2, 2, 2);
imshow(binaryImage, []);
title('Initial Binary Image', 'FontSize', fontSize, 'Interpreter', 'None');
axis('on', 'image');

% Skeletonize the image.
skelImage = bwmorph(binaryImage, 'skel', inf);
% Display the image.
subplot(2, 2, 3);
imshow(skelImage, []);
title('Skeleton Image', 'FontSize', fontSize, 'Interpreter', 'None');
axis('on', 'image');

[sali]

Thanks I tried the code and it works, so what I understood that my image is not already black and white it is considered as RGB, so first it should be converted to grey scale then to binary img which is black and white, Am I right?

[sali]

I was using this piece of code (regardless of scaling the image) is this right? I want to have a black and white image and deal with the black as 1 and white as -1 then reverse result at the end of my code which is not included here for simplicity.

I = imread('image1.png');
level = graythresh(I);
BW = im2bw(I,level);
A = BW(1:100,1:100);
imageData = int8(A);
 for i=1:100
    for j=1:100
        if(imageData(i,j)==0 )
            imageData(i,j)=1;
        else if ( imageData(i,j)==1)
                imageData(i,j)=-1;
            end
        end
    end
end

Answer 2

[Matt J]

I think what you are asking is if there is a way to reduce the image of the lines to 1 pixel in width. If so, you can use bwskel or

bwmorph(BW,'skel',inf)

[sali]

Thanks for your reply, yes this what I meant , I'll try this function. Thank you so much

[sali]

Shall I do this, before going forward to process the image

image = imread("....../file.jpg");
image= bwmorph(BW,'skel',inf);
imshow(image);

[Image Analyst]

Definitely not. DO NOT use image as a variable name since that's a built-in function that you'd destroy.

[sali]

Do you mean this piece of code is right except the variable name which should not be “image”?

[Image Analyst]

No, there are still things wrong with it even if you fixed that. See my code below for a correct version.