Creating a white outline of an image

I have this image (below and attached) that I'd like to create a white-line outline around the gray portion, preferably one that I can overlay onto other images in the same manner without the gray portion seen. Any thoughts on how I could do that? Happy to clarify as needed.

Answer 1

[Image Analyst]

Try this:

% Demo by Image Analyst, March, 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 = 'Example_03192021.png';
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 Gray Scale 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 rid of huge white surrounding frame by cropping out the central portion.
grayImage = grayImage(41 : 466, 72 : 483);
%--------------------------------------------------------------------------------------------------------
% Get histogram
subplot(2, 3, 2);
counts = histcounts(grayImage);
bar(counts, 1);
grid on;
title('Log Histogram of gray scale image', 'FontSize', fontSize);
xlabel('Gray Level', 'FontSize', fontSize);
ylabel('Count', 'FontSize', fontSize);

% Threshold image.
mask = grayImage > 2;
% Display mask image.
subplot(2, 3, 3);
imshow(mask, []);
axis('on', 'image');
title('Mask (Binary Image)', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
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, 4);
% 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);
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
caption = sprintf('%d Labeled Blobs', numberOfBlobs);
title(caption, '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);

% Get the image of the perimeters.
mask = bwperim(mask);
% Display mask image.
subplot(2, 3, 5);
imshow(mask, []);
axis('on', 'image');
title('Final Boundaries', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.

fprintf('Done running %s.m\n', mfilename);