Re: spatial and frequency domain

fulltime:
You don't do convolution in the frequency domain. You do
multiplication. Roughly speaking, you can do the same operation
either (1) by convolving in the spatial domain, or (2) multiplying in
the frequency domain (multiplying the ft of the convolution kernel by
the ft of the scene). For very large images or complicated and
precise filtering, you'd multiply in the frequency domain and for
simple things like blurring and edge detection you do those in the
spatial domain via convolution. Periodic signals show up in the freq
domain as spikes. For example, a honeycomb pattern will appear as a
hexagonal array of spikes. You can multiply your spikes by zero to
remove the periodic signal (after inverse transforming, the periodic
appearance will be "gone"). (E.g. zero out the hexagon spikes and
inverse transform and you'll have a uniform image.)
Regards,
ImageAnalyst

On Mar 5, 1:20 pm, "fulltime" <PiaoCh...@xxxxxxxxx> wrote:
Hi experts,

I wanted to find out more abt 2D convolution of images but ended up
getting confused about these 2 terms, spatial and freq domain.

I am confused abt spatial and frequency domain and i have doubts as to
which domain should my filtering be performed.

I have designed a 1D FIR filter, used frequency transformation method
in matlab to convert it to 2D FIR filter. I want to apply this filter
to the image, but my question is, "is any form of transformation
needed before i perform conv2? if no transformation is needed, does
that mean my "conv2" is performed in the spatial domain?

f = [0 0.7 0.85 1]
a = [0 0 1 1]
coe = remez (50, f, a)
coeTwo = ftrans2(coe);
result = conv2(Image,coeTwo);

under which circumstances do i need to perform filtering in frequency
domain?

CONV of image in spatial domain is to move the filter mask along the
entire image and compute the summation of weighted average from all
its neighbours. how abt conv in freq domain?

I am new to image processing n please forgive me if i sound silly, but
i just cant find ans to my qn after searching the net for the past 5
hrs. appreciate any help given

Thanks.
FT


.

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