extract the region of interest in a color image

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Gobert 2020-9-9

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https://ww2.mathworks.cn/matlabcentral/answers/591322-extract-the-region-of-interest-in-a-color-image

评论： Image Analyst 2020-9-11

I would like to change image A into image B using Matlab. I only need that specific region, shown in B, located between green and red contours. Can you please help?

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Answer 1

Image Analyst 2020-9-9

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https://ww2.mathworks.cn/matlabcentral/answers/591322-extract-the-region-of-interest-in-a-color-image#answer_492319

freehand_masking_demo.m

Since it's not clear where the boundary of the region is in the upper left, I suggest you manually trace it out. I'm attaching a demo.

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Image Analyst 2020-9-11

在 MATLAB Online 中打开

That's because your green and red were not pure green and red, like with values of 255. They were "greenish" and "reddish". Here, try this:

% Demo to find distances.  By Image Analyst, May 5, 2020.
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 = 'image.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
rgbImage = imread(fullFileName);
[rows, columns, numberOfColorChannels] = size(rgbImage)
% Display the test image.
subplot(4, 2, 1);
imshow(rgbImage, []);
axis('on', 'image');
caption = sprintf('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';
% Split the image into color channels.
[r, g, b] = imsplit(rgbImage);
% Then find a green and red mask
threshold1 = 100;
threshold2 = 150;
greenMask = (r <= threshold1) & (g >= threshold2) & (b <= threshold1);
redMask = (r >= threshold2) & (g <= threshold1) & (b <= threshold1);
% Display the mask images.
subplot(4, 2, 2);
imshow(greenMask, []);
axis('on', 'image');
title('Green Mask', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
subplot(4, 2, 3);
imshow(redMask, []);
axis('on', 'image');
title('Red Mask', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
% Then fill the masks
greenMask = imfill(greenMask, 'holes');
redMask = imfill(redMask, 'holes');
% Take largest blob only
greenMask = bwareafilt(greenMask, 1);
redMask = bwareafilt(redMask, 1);
% Display the mask images.
subplot(4, 2, 4);
imshow(greenMask, []);
axis('on', 'image');
title('Green Mask', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
subplot(4, 2, 5);
imshow(redMask, []);
axis('on', 'image');
title('Red Mask', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
% Now erase the red mask from within the green mask, leaving the donut.
finalMask = greenMask; % Initialize.
finalMask(redMask) = false; % Erase the red mask.
subplot(4, 2, 6);
imshow(finalMask, []);
axis('on', 'image');
title('Final Mask', 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.
% Mask the image using bsxfun() function to multiply the mask by each channel individually.  Works for gray scale as well as RGB Color images.
maskedRgbImage = bsxfun(@times, rgbImage, cast(finalMask, 'like', rgbImage));
% Display the mask images.
subplot(4, 2, 7:8);
imshow(maskedRgbImage, []);
axis('on', 'image');
caption = sprintf('Masked 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.

Gobert 2020-9-11

This is great! Thank you! @Image Analyst

Image Analyst 2020-9-11

Then please "Accept this answer" if you think we're done here and don't think you'll get any better/more answers. Thanks in advance.

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extract the region of interest in a color image

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extract the region of interest in a color image

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