fourier transform of image

command run 1:

octave:1> imga=imread('/home/hp/Downloads/1.jpg');
octave:2> imshow(imga)
octave:3>figray=fft2(imga); //figray is complex

octave:4>imshow(figray)

octave:9> imshow(abs(figray),[])

We can shift the quadrant back to its proper place by using the command 

imshow(fftshift(abs(figray))), [])

imshow(fftshift(abs(figray)))

Now we can inverse the transform we used by using another FFT. 

imshow(abs(fft2(fft2(Imga))));

it may look like the original circle but it is already inverse of the original. image. We can see it more clearly by doing the same things done on the circle to the image with the letter 'A'.

octave:26> imgb=imread('/home/hp/Downloads/6.jpg');

octave:28> imshow(imgb)

octave:29> fftb=fft2(imgb);

octave:30> imshow(fftb)

warning: imshow: only showing real part of complex image

octave:31> imshow(abs(fftb)); image obtained is white as below

octave:32> imshow(abs(fftb),[]); image obtained is same as white above