[rescue] Spaceballs.

[Scott Newell]

Dave McGuire wrote:

>  The time domain for a single image (take a single-channel image for
>simplicity) is luminance.  Look at it this way...take an image as a
>2-d array of integer pixels.  Iterate through the rows and columns
>sequentially, as they would be stored in memory.  Plot the luminance
>(the integer pixel value).  Bang, there's your time-domain signal.

I guess you could do that, but all the lit I've seen on image processing
uses the two dimensional Fourier transform, which has a double integral
(continuous space) or double summation (discrete space).  

What you propose would not be rotational invariant--vertical bands would
contain significant high frequency energy (as it should--it's a sharp
edge), since your iteration would see the deltas as sequential samples in
the time domain.  However, the iteration would screw with horizontal bands,
'cause you wouldn't get to a transition until you'd iterated over the
entire row.  (I'm sorry if that doesn't make sense--I'd almost need to draw
sketches to explain.)


newell