# Jan

### Fraunhofer IAF

Professional Interests: signal processing, image analysis, machine learning

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**Content Feed**

how to strengthen the image ?

I gather you are working with single channel black and white images, i.e. pixel values are either 0 or 1. In that case, what you...

9 years ago | 0

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how to write the code for dividing pixel values of an image with the mean pixel value?

To scale each pixel vector in hyperspectral image _X_ with the global data mean simply do X = X ./ mean( X(:) );

9 years ago | 0

Include function in gui m-file or separate them?

For a cleaner structure I would allways outsource functionality in seperate .m files. For me (in Matlab as in any other programm...

9 years ago | 0

Hi. What is the difference between xcorr and crosscorr?

Two different Toolboxes. _crosscorr_ is from the econometrics toolbox, while _xcorr_ is delivered with the signal processing too...

9 years ago | 0

extracting a row from a matrix

M = [1,2,3;1,1,4;2,1,2;3,2,5]; [~, max_idx] = max( M(:,end) ); max_row = M(max_idx,:);

9 years ago | 0

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how to fill polygone with circles without intersect with each other

I would assume, that your problem is not the actual coding, but the algorithm to use for solving this non-trivial task. Especial...

9 years ago | 0

speech analysis in matlab

For analyzing one specific audio recording, I would try to threshold the signal energy level. However, as far as I remember it c...

9 years ago | 0

substitute each element of a vector into a matrix without using loop

Like this? vector = 1:1:10; vector = reshape( vector, [1, 1, numel(vector)] ); one_vector = ones( 1, 1, numel(vector) )...

9 years ago | 0

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substitute each element of a vector into a matrix without using loop

Maybe something like the following? matrix = [4, 5; 4, 2]; [p, q] = size( matrix ); vector = 1:1:10; matrix = repma...

9 years ago | 0

How can i use threshold to convert a gray-scaled image into binary image ?

This is straightforward: A = imread('cameraman.tif'); % example grayscale image threshold = 120; % custom threshold val...

9 years ago | 1

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Array in array in image??

To get the non-zero elements of an array simply do something like: A = randn(100, 100); A_non_zero = A( A~=0 ); This...

9 years ago | 0

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spatial coordinates of BW image

Use _find()_ e.g. A = randn(100,100) > .5; % example binary image [row col] = find( A == 1 ); res = [ row col ]; ...

9 years ago | 0

how to find spatial frequency of color image

You probably want to analyze the structure of the image's 2d fourier transform using _fft2()_. Either for each channel or after ...

9 years ago | 0

display values in the title of a figure

title(['Mean', num2str( mean(mean(aa(:,:)))) ]) or shorter: title ( ['Mean ', num2str( mean( aa(:) ) ) ] );

9 years ago | 0

how can I improve FFT resolution

You can use _zero padding_ (simply add zero values to your signal prior to FFT). Note that this does not provide additional info...

9 years ago | 0

How to retrieve data from the textboxes of a GUI created with GUIDE.

You can access the content of a textbox in any function that has access to the _handles_ object. For instance if you want to acc...

9 years ago | 0

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How do I plot the impulse response from this equation?

Maybe you want to do something like: h = [1, 3, -2, 9, 7]; ft_h = fft( h ); ft_h = sqrt( ft_h .* conj( ft_h ) )...

9 years ago | 0

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selecting elements in the matrix

Use [row, col] = find(A>6) to find row and column indeces and use v = A( A>6 ); to get the corresponding values....

9 years ago | 0

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How to insert artificial Artifacts in EEG signals ?

This is a very general question. In general, you will need a sample of an EOG artifact. That you can add to the EEG channels a...

9 years ago | 0

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put a mall matrix in a big matrix

A( 1: 1 + size(B,1)-1, 5377 : 5377 + size(B, 2) - 1 ) = B;

9 years ago | 0

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Numerical integration over a circular domain

I would try to transform the scalar field into polar coordinates and do numerical integration over a square window there. Of cou...

9 years ago | 0

How do i obtain only the first principal component?

I'm not sure, if I fully understand your question. I doubt however, that there is a straightforward method for calculating the e...

9 years ago | 0

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I'm not understanding why this error occurs: Error: Unexpected MATLAB expression

You are missing a multiplication operator: Try newton(x^3-x,3 * x^2-1,-1,1e-5,20) ^ in...

9 years ago | 1

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stopping matlab from re-formating my numbers!!!

Use the _format_ argument when calling _num2str_ e.g. z = num2str( x, '%4.10f' ) if you want 10 (ten, not three ;) ) ...

9 years ago | 0

How to prevent any variable from displaying its name?

Use a semicolon on the end of each line, e.g.: a = 1 + 1; disp( num2str(a) );

9 years ago | 0

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Undefined function or variable 'slm'. = QUICK HELP!

The error message quite correctly states, that you never defined the variable _slm_ before you try to use it as an argument for ...

9 years ago | 0

Convert a 3-d matrix to a 2-d matrix

b = zeros( size(a, 1), size(a, 2) ); for i = 1 : size(a, 3); b = b + 10.^(size(a, 3) - i) * a(:,:,i); end;

9 years ago | 0

Meaning of the symbol in the equation

you are looking at the square of a vector norm: |||v|||^2 = sqrt( v_1^2 + v_2^2 + ... + v_n^2 ) = v_1^2 + v_2^2 + ... + v_n^...

9 years ago | 1

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sigmoid function value for parameter a and b

According to my calculations you have to pick _0<b<1_ and _a>0_. E.g. b=1/2 and a=1

9 years ago | 1

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