On Fri, Nov 18, 2011 at 8:47 AM, Ben Abbott
<address@hidden> wrote:
On Nov 18, 2011, at 8:45 AM, Przemek Klosowski wrote:
> On 11/17/2011 04:42 PM, Yaowang wrote:
>
>> octave:1> x=imread('1149.tiff')
>> octave:2> imshow(x)
>> octave:3> y=fft(x);
>> octave:4> imshow(y)
>> warning: imshow: only showing real part of complex image
>> octave:5> imwrite("1149.img",y)
>
> It's the second time in few weeks when someone tries to display and save FFTs of images. That doesn't make any sense to me---is there something I'm missing here? Is it some kind of image processing trick that treats Fourier coefficients as an image on its own?
I think you are correct.
Ben
Yes, its a common way in computer vision to visualize the 2D fft of an image. Image compression techniques frequently use this to reduce the size of an image, for example.
What students tend to forget is that while the signal is real, the fft need not be. Thus what is usually plotted is absolute value of the fft. IIRC, its because our eyes don't really care all that much about the phase of the fft, but the magnitude.