Gaussian filter in MATLAB

Question

Does the  gaussian  filter in MATLAB convolve the image with the Gaussian kernel  Also  how do you choose the parameters hsize  size of filter  and sigma  What do you base it on

User · Answer

In MATLAB R2015a or newer  it is no longer necessary  or advisable from a performance standpoint  to use fspecial followed by imfilter since there is a new function called imgaussfilt that performs this operation in one step and more efficiently   The basic syntax      B   imgaussfilt A sigma  filters image A with a 2-D Gaussian smoothing kernel with standard deviation specified by sigma    The size of the filter for a given Gaussian standard deviation  sigam  is chosen automatically  but can also be specified manually   B   imgaussfilt A sigma  FilterSize   3 3      The default is 2 ceil 2 sigma  1   Additional features of imgaussfilter are ability to operate on gpuArrays  filtering in frequency or spacial domain  and advanced image padding options   It looks a lot like IPP     hmmm   Plus  there s a 3D version called imgaussfilt3

User · Answer

You first create the filter with fspecial and then convolve the image with the filter using imfilter  which works on multidimensional images as in the example   You specify sigma and hsize in fspecial  Code      Read an image I   imread  peppers png       Create the gaussian filter with hsize    5 5  and sigma   2 G   fspecial  gaussian   5 5  2      Filter it Ig   imfilter I G  same       Display imshow Ig

User · Answer

Jacob already showed you how to use the Gaussian filter in Matlab  so I won t repeat that   I would choose filter size to be about 3 sigma in each direction  round to odd integer   Thus  the filter decays to nearly zero at the edges  and you won t get discontinuities in the filtered image   The choice of sigma depends a lot on what you want to do  Gaussian smoothing is low-pass filtering  which means that it suppresses high-frequency detail  noise  but also edges   while preserving the low-frequency parts of the image  i e  those that don t vary so much   In other words  the filter blurs everything that is smaller than the filter    If you re looking to suppress noise in an image in order to enhance the detection of small features  for example  I suggest to choose a sigma that makes the Gaussian just slightly smaller than the feature

[matlab] Gaussian filter in MATLAB

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