MATLAB: Thresholding a value in matrix

maskingmatrixthresholding

I had been given a 8×8 matrix. How can I theshold a value in the matrix?

for example 100 or 255. Thank you.

Best Answer

You can use the comparator operators to apply a threshold:

data=randi(200,8,8);
L= data<100; %L is true for all positions with a value below 100
data2=data;%make a copy
data2(L)=200 %edit only some values
data2 = 8×8
   189   200   200   200   200   200   155   160
   200   200   200   200   200   189   132   200
   200   200   123   128   200   173   200   101
   200   200   200   156   157   200   169   200
   200   200   200   147   117   200   157   163
   164   172   101   134   170   200   200   196
   200   165   200   123   118   195   200   200
   118   200   200   200   200   200   183   200
●

Related Solutions

MATLAB: How to delete a row of a matrix if value in a particular column is less than a specified value

Hello,

You can use this one liner,

datanew = data(data(:,1)>=4,:);

However, I chose to reverse the logic here, so instead of less than 4, you should write greater than or equal to (it's selecting the ones to keep).

Also, the data(:,1) is using the first column (just to be clear).

Hope this helps!

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 delete a row of a matrix if value in a particular column is less than a specified value

MATLAB: Threshold

Related Question