how i can implement lowpass filter on image using matlab

how i can implement lowpass filter on image using matlab when we implement the fractal image compressin we need to do that ,how i can do it plz help me

Answer 1

[Image Analyst]

One way is to just convolve with a kernel that has all positive weights, like a box filter:

boxKernel = ones(21,21); % Or whatever size window you want.
blurredImage = conv2(grayImage, boxKernel, 'same');

imfilter() does a similar (though not exact) thing. The more pointed the filter is in the middle, the less filtering it will do, and the bigger the window size, the more blurring it will do. For example, a Gaussian filter does less blurring (filtering) than a box filter of the same window size. A bigger box (e.g. 31 x 31) will blur more than a smaller one (e.g. 3 x 3).

You can do other, non-linear filters in the spatial domain. You can do linear filtering in the Fourier domain if you want to and have reason to, like you have known frequencies you want to remove, or you have a periodic structure you want to get rid of.

[Image Analyst]

P.S. Let me know if you want my Fourier filtering demo.

[ramin bba]

Dear Image Analyst,

Could you please upload your Fourier filtering demo?

tnx

[Image Analyst]

See attached.

Answer 2

[David Young]

If you want to smooth with a Gaussian kernel, as already suggested, you might find gsmooth2, available here, helpful. It only does the equivalent of calling fspecial and imfilter, but it handles some of the details for you, which can be convenient.

Answer 3

[Amith Kamath]

I am assuming you need to smooth (low pass) an image. These two functions are what you need to use:

http://www.mathworks.com/help/images/ref/imfilter.html

and

http://www.mathworks.com/help/images/ref/fspecial.html

specifically, the 'gaussian' filter.