how to display an image for threshold value greater than certain level ?

In my code, i wished to keep threshold value as 150. I want to display the image only for values greater than 150. What should be the code?

Answer 1

[Image Analyst]

You just use logical indexing, like this:

binaryImage = grayImage > 150;
maskedImage = grayImage;
maskedImage(~binaryImage) = 0;  % Zero out where mask is 0.

Here's a full-blown demo:

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.
format longg;
format compact;
fontSize = 20;

% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'moon.tif';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
  % File doesn't exist -- 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 in the search path folders.', 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, 'units','normalized','outerposition',[0 0 1 1]);
% Give a name to the title bar.
set(gcf,'name','Demo by ImageAnalyst','numbertitle','off') 

binaryImage = grayImage > 150;
% Display the binary mask image.
subplot(2, 2, 2);
imshow(binaryImage, []);
title('Binary Mask Image', 'FontSize', fontSize);

% Get a masked image.
maskedImage = grayImage;  % Initialize.
maskedImage(~binaryImage) = 0;  % Zero out where mask is 0.
% Display the binary mask image.
subplot(2, 2, 3);
imshow(maskedImage, []);
title('Masked Grayscale Image', 'FontSize', fontSize);