MATLAB: Sinusoid identification in images

Image Processing Toolboxsinusoid pattern recognition

I am wondering whether there is a tool in Matlab that identifies sinusoids in an image. I saw that the Hough function allows to find lines so maybe there is a similar tool for sinusoids.

Thx

Jan

Best Answer

Every image has sinusoids in it. Hundreds of them. And the Fourier transform gives you the strength of each sinusoid. The FT is basically a plot of sinusoid amplitude versus its frequency. If you want, you can look for a value (strength of a particular frequency) that is way greater than other frequencies. I have an fft2d() demo - let me know if you want me to post it.

Related Solutions

MATLAB: How to remove the pattern from microscopy scanned image

Well obviously sharpening the image won't remove the stripes - if anything it will just make it worse.

Look at the log magnitude of the spectrum. See those spikes? Just erase those and inverse transform. I'm attaching a similar example that you can adapt.

MATLAB: How to display the input image, after when the threshold values exceeds certain limit

It's just 3 lines. Just mask the original image:

binaryImage = grayImage > 150;
maskedImage = zeros(size(grayImage)); % Initialize.

maskedImage(binaryImage) = grayImage(binaryImage);

See the full demo below:

% Demo by ImageAnalyst
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
fontSize = 14;
% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'coins.png';
% 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') 
% Let's compute and display the histogram.
[pixelCount grayLevels] = imhist(grayImage);
subplot(2, 2, 2); 
bar(pixelCount);
grid on;
title('Histogram of original image', 'FontSize', fontSize);
xlim([0 grayLevels(end)]); % Scale x axis manually.
yl = ylim();
line([150 150], [0 yl(2)], 'Color', 'r');
% Threshold at 150
binaryImage = grayImage > 150;
% Display the original gray scale image.
subplot(2, 2, 3);
imshow(binaryImage, []);
title('Binary Image', 'FontSize', fontSize);
% Mask the image
maskedImage = zeros(size(grayImage)); % Initialize.
% Assign values from grayImage that are > 150.
maskedImage(binaryImage) = grayImage(binaryImage);
% Display the original gray scale image.
subplot(2, 2, 4);
imshow(maskedImage, []);
title('Masked Image', 'FontSize', fontSize);

Best Answer

Related Solutions

MATLAB: How to remove the pattern from microscopy scanned image

MATLAB: How to display the input image, after when the threshold values exceeds certain limit

Related Question