# Filtering + Images [duplicate]

Possible Duplicate:
What does frequency domain denote in case of images?

I am studying applications of low and high pass filters in images. However, first I'm trying to understand what exactly low and high frequencies are in images.

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## marked as duplicate by Abid Rahman K, jonsca, Paul R, penelope, Lorem IpsumJan 6 '13 at 22:27

As jonsca stated, frequency can be understood as a rate of change.

Particularly, in images you can say that the high frequencies are the details of the image. Higher frequency, more "edgy" image.

This can be easily seen if you apply some transformations to frequency domain to images, filter them, and them transform them back.

If you have this image:

A high-frequency component could be:

And a low-frequency one:

The low-pass filtered image has 'lost detail' and the high-pass filtered one has 'lost smoothness'

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And for the few not familiar with the famous (or infamous) 'Lenna' picture, there are a bunch of links: ndevilla.free.fr/lena ee.cityu.edu.hk/~lmpo/lenna/Lenna97.html en.wikipedia.org/wiki/Lena_S%C3%B6derberg –  Kevin McGee Dec 30 '12 at 5:31