CODEWITHSUNDEEP
image-processingcomputer-visionfft
dariush
dariush

Reputation: 3341

What does an image of Fourier Transformation of an image tell us?

First time studying image processing...
I just don't understand what does fourier transformed image of an image describe?
For example consider given following pictures, The first one is the image, and the second one is the fourier transformation of the image.

The Lena image The fourier transformation of lena

Now my question is:
By given the fourier transformation image, what am i suppose to comprehend from that?

I would really appreciate any help here, i just cannot proceed with my studies without understanding this.

Thanks in advance.

Upvotes: 3

Views: 1754

Answers (1)

lennon310
lennon310

Reputation: 12689

The central part includes the low frequency components. The bright pixels in frequency image (right) indicate strong intensity at the corresponding positions in spatial image (left). Note that there is no one-on-one mapping from the pixel in frequency domain and spatial domain. One frequency pixel consists all the spatial pixels that have the corresponding frequency.

The low frequency domain corresponds to the smooth areas in the image (such as skin, hat, background, etc). The high frequency domain, which is shown in the image away from the central part, includes those sharp edges or some structure with the changes of intensity dramatically along one orientation (such as the hairs, boundary of hat, etc). But since the intensity for those parts is not high enough compared with the smooth structure, the corresponding regions appear dark on the right image.

Note that the camera lens focuses on Lenna, so the background is blurred. If the focus region is at background, the vertical lines behind Lenna would be clear, and the sharp edges of the lines will contribute to high frequency magnitude, thus region away from the center on the right image would be bright.

Upvotes: 2

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