MATLAB: Image thresholding using min and max pixel intensity values

image processingImage Processing Toolboxthresholding

Hi,

I'm trying to create a mask based on a minimum and maximum intensity value. All the examples I find are basically thresholding the image from a fixed value (say, 176) to 255. What I need to do is to mask pixels between 165 and 166 to find ROIs on the image.

Thanks!

Best Answer

Try this:

mask = grayImage >= 165 & grayImage <= 166 % Mask of only pixels with GLs of 165 and 166
grayImage(~mask) = 0; % blacken outside the mask.

Related Solutions

MATLAB: How to find maximum pixel intensity of the two regions obtained after finding the threshold of the image

Try something like this

% grayImage = imread('cameraman.tif');
someThreshold = 190;
binaryImage = grayImage < someThreshold;
labeledImage = bwlabel(binaryImage);
measurements = regionprops(labeledImage, grayImage, 'MaxIntensity');
maxIntensities = [measurements.MaxIntensity]

That gives a blob-by-blob accounting of the max. If you just want the max of the image above and below the threshold, you can simply do this

mask = grayImage < someThreshold;
maxAbove = max(grayImage(mask))
maxBelow = max(grayImage(~mask))

MATLAB: Threshold

See my demo (simply copy and paste):

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
fontSize = 20;
% Change the current folder to the folder of this m-file.
if(~isdeployed)
  cd(fileparts(which(mfilename)));
end
  
% Check that user has the Image Processing Toolbox installed.
hasIPT = license('test', 'image_toolbox');
if ~hasIPT
  % User does not have the toolbox installed.
  message = sprintf('Sorry, but you do not seem to have the Image Processing Toolbox.\nDo you want to try to continue anyway?');
  reply = questdlg(message, 'Toolbox missing', 'Yes', 'No', 'Yes');
  if strcmpi(reply, 'No')
    % User said No, so exit.
    return;
  end
end
% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'cell.tif';
fullFileName = fullfile(folder, baseFileName);
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
  % Didn't find it there.  Check the search path for it.
  fullFileName = baseFileName; % No path this time.
  if ~exist(fullFileName, 'file')
    % Still didn't find it.  Alert user.
    errorMessage = sprintf('Error: %s does not exist.', fullFileName);
    uiwait(warndlg(errorMessage));
    return;
  end
end
grayImage = imread(fullFileName);
% Get the dimensions of the image.  numberOfColorBands should be = 1.
[rows columns numberOfColorBands] = size(grayImage);
% Display the original gray scale image.
subplot(2, 2, 1);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'Position', get(0,'Screensize')); 
set(gcf,'name','Demo by ImageAnalyst','numbertitle','off') 
% Threshold the image.
binaryImage = grayImage >= 70 & grayImage <= 130;
% Display the binary image.
subplot(2, 2, 2);
imshow(binaryImage, []);
title('Binary Image', 'FontSize', fontSize);
% Mask the image.
maskedImage = grayImage; % Initialize.
maskedImage(~binaryImage) = 0;
% Display the masked image.
subplot(2, 2, 3);
imshow(maskedImage, []);
title('Masked Image', 'FontSize', fontSize);
msgbox('Done with demo!');

Best Answer

Related Solutions

MATLAB: How to find maximum pixel intensity of the two regions obtained after finding the threshold of the image

MATLAB: Threshold

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