MATLAB: Extract the INNER white region of an image with black and white intersection.

8 or 4-connectedimage analysisimage processingImage Processing Toolboximage segmentationMATLAB

Hello,

I would like to get the inner part of the white region in the image below, the region I want is the red rectangluar part (INNER part of the white region). I do not want the outter part of the white region.

However, with my code below, I can only get the out part of the white region, is there anyone can help me?

Thanks a lot.

%%%%%My code
I = imread(filename);
Igray = rgb2gray(I);
BW2 = Igray < 50;
% Detect rectangle region (inside the line)
BW2 = imclearborder(~BW2);
BW2 = bwareafilt(BW2,1);
% Calculate bounding box
props2= regionprops(BW2,'BoundingBox');
boundingBox2 = props2.BoundingBox;
figure
imshow(BW2)

Best Answer

First of all you don't need imclearborder because there is no part of your blob that touches the border. And after bwareafilt() you're probably still getting the original blob because some of the outer blobs are touching your inner blob by having the corners of the pixels touch. The default for bwareafilt() is 8-connected, which considers blobs touching on the diagonal to be the same blob. You should specify the "4-connected" option so that a blob is only connected if it's fully touching on the top, bottom, left, or right (not the diagonal/corner).

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MATLAB: Obtain average image threshold without the background

Try this:

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 = 22;
%--------------------------------------------------------------------------------------------------------

%    READ IN IMAGE
folder = pwd;
baseFileName = 'image.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
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, 2, 1);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize, 'Interpreter', 'None');
impixelinfo;
hFig = gcf;
hFig.WindowState = 'maximized'; % May not work in earlier versions of MATLAB.
drawnow;
%--------------------------------------------------------------------------------------------------------
%    SEGMENTATION OF IMAGE
% Get a binary image of just the blob and not including the black background or the white surround.
mask = grayImage > 0 & grayImage < 255;  %imbinarize(grayImage);
subplot(2, 2, 2);
imshow(mask, []);
impixelinfo;
title('Initial Mask Image', 'FontSize', fontSize, 'Interpreter', 'None');
impixelinfo;
% Display histogram of image but only the image within the mask
subplot(2, 3, 4);
histogram(grayImage(mask), 0:255);
grid on;
title('Histogram of gray image', 'FontSize', fontSize);
% Now get the threshold
thresh = 255 * graythresh(grayImage(mask))
% Put a red line there at the threshold
xline(thresh, 'Color', 'r', 'LineWidth', 2);
% Get a binary image of the bright stuff
brightStuff = grayImage >= thresh & mask;
subplot(2, 3, 5);
imshow(brightStuff, []);
impixelinfo;
title('Bright Pixels in Region', 'FontSize', fontSize, 'Interpreter', 'None');
impixelinfo;
subplot(2, 3, 6);
darkStuff = ~brightStuff & mask;
imshow(darkStuff, []);
impixelinfo;
title('Dark Pixels in Region', 'FontSize', fontSize, 'Interpreter', 'None');
impixelinfo;

MATLAB: Is their any way to calculate automatically this parameter from the image

Of course it's possible. Try this. Adapt as needed:

% Demo by Image Analyst, February, 2021.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clearvars;
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 16;
fprintf('Beginning to run %s.m ...\n', mfilename);
%-----------------------------------------------------------------------------------------------------------------------------------
% Read in image.
folder = [];
baseFileName = 'original image.JPG';
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
grayImage = imread(fullFileName);
[rows, columns, numberOfColorChannels] = size(grayImage)
if numberOfColorChannels == 3
	grayImage = rgb2gray(grayImage);
end
% Display the test image full size.
subplot(2, 3, 1);
imshow(grayImage, []);
axis('on', 'image');
caption = sprintf('Original Image : "%s"', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.



% Set up figure properties:
% Enlarge figure to full screen.
hFig1 = gcf;
hFig1.Units = 'Normalized';
hFig1.WindowState = 'maximized';
% 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.
hFig1.Name = 'Demo by Image Analyst';
%--------------------------------------------------------------------------------------------------------
% Get histogram
subplot(2, 3, 2);
imhist(grayImage);
grid on;
xlabel('Gray Level', 'FontSize', fontSize);
ylabel('Count', 'FontSize', fontSize);
% Threshold image.
mask = grayImage < 75;
% Clean up the mask to get only the stripes we want.
mask(:, 1 : 762) = false;
mask(:, 2615 : end) = false;
% Get rid any blob not 1500 wide
labeledImage = bwlabel(mask);
props = regionprops(labeledImage, 'BoundingBox');
allBB = vertcat(props.BoundingBox);
widths = allBB(:, 3);
wideBlobs = find(widths > 1500);
% Extract only those that are wide enough.
mask = ismember(labeledImage, wideBlobs);
% Display mask image.

subplot(2, 3, 3);
imshow(mask, []);
axis('on', 'image');
title('Mask', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hold on;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
% Label each blob with 8-connectivity, so we can make measurements of it
[labeledImage, numberOfBlobs] = bwlabel(mask, 8);
% Apply a variety of pseudo-colors to the regions.
coloredLabelsImage = label2rgb (labeledImage, 'hsv', 'k', 'shuffle');
% Display the pseudo-colored image.
subplot(2, 3, 4);
imshow(coloredLabelsImage);
title('Labeled Blobs', 'FontSize', fontSize, 'Interpreter', 'None');
% Get all the blob properties.  Can only pass in originalImage in version R2008a and later.
blobMeasurements = regionprops(labeledImage, grayImage, 'all');
numberOfBlobs = size(blobMeasurements, 1);
% For each blob, for each line, get the left edge and right edge then widths.
leftEdges = zeros(1, columns);
rightEdges = zeros(1, columns);
widths = zeros(columns, numberOfBlobs);
for blob = 1 : numberOfBlobs
	thisBlob = ismember(labeledImage, blob);
	% Display mask image.
	subplot(2, 3, 5);
	imshow(thisBlob, []);
	axis('on', 'image');
	caption = sprintf('Mask of Blob #%d of %d', blob, numberOfBlobs);
	title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
	drawnow;
	hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
	for col = 1 : columns
		thisCol = thisBlob(:, col);
		t = find(thisCol, 1, 'first');
		if ~isempty(t)
			leftEdges(col) = t;
			rightEdges(col) = find(thisCol, 1, 'last');
		end
	end
	widths(:, blob) = (rightEdges - leftEdges)';
	subplot(2, 3, 6);
	plot(widths, '-', 'LineWidth', 1);
	hold on;
	grid on;
	drawnow;
	legendStrings{blob} = sprintf('Blob #%d', blob);
end
grid on;
title('Widths', 'FontSize', fontSize, 'Interpreter', 'None');
xlabel('Row', 'FontSize', fontSize);
ylabel('Width in Pixels', 'FontSize', fontSize);
legend(legendStrings);
% Display mask image again.
subplot(2, 3, 5);
imshow(mask, []);
axis('on', 'image');
title('Mask', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hold on;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
fprintf('Done running %s.m\n', mfilename);

Best Answer

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MATLAB: Obtain average image threshold without the background

MATLAB: Is their any way to calculate automatically this parameter from the image

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