what does it mean "windowing and truncation in fequency domain "

how truncation is performed on image using different windows and does that window size depend on original image

Answer 1

[Image Analyst]

Basically you multiply the FFT (spectrum, Fourier Domain) by something that zeros out or attenuates higher frequencies. This "truncates" the spectrum. You choose the window size. It does not depend on the original image size, except that if the width of the truncating window is too huge (wider than the spectrum), you wouldn't be truncating anything. So in a very indirect way it depends on the image size (because hte spectrum size depends on the image size and thus the largest truncating window depends on the image size), but not really directly.

[Zuhaib]

if you do not mind then suggest me window size for 515*512 image and tell me how to generate that because i am at beginner level of image processing in Matlab

[Image Analyst]

I suggest you try a variety of windows such as 32 by 64, 8 by 128, 16 by 16, and observe in each case how it affects the image, and try to understand why.

[Zuhaib]

thank you for your assistance

Answer 2

[Arthur]

I used some thing like your question when i worked with Fourier transform. And the analysis could be on the frequecy domain (frequency spectrum)

Or a window of a cicle is used to generate the RMS value of a wave of many of cicles. step by step. (its a way of windowing).

I did not sure if it is your question.

[Zuhaib]

first point you had said is correct in my case that i am working on Fourier transform and its analysis but i do not want its RMS value or window of cicle ..... i want to generate window like hamming window . the main thing is that i want to make sure does parameter of window depend on image ???

[Image Analyst]

But it doesn't. You can choose whatever window size you want.

[Arthur]

ok! I think it does not need, but I think it would facilitate the work if it were integer multiple of the main image. As the friend suggested

[Image Analyst]

Nothing will be facilitated. Integer multiple (which of course won't have any effect whatsoever) or integer divisor (which is what I think you meant) - none of those are any better or easier than picking some arbitrary window width. It just doesn't matter.