Re: spectrogram...but for images?

On Jan 13, 5:36 am, -G- <-...@xxxxxxxxxxxxxxxxxx> wrote:
ImageAnalyst wrote:
On Jan 8, 8:38 pm, "MZ" <m...@xxxxxxxxxxx> wrote:
I have an image.  I want to evaluate the spatial frequency components as
a function of position in the image.
Sounds confusing.  Are you saying that you'd like a Fourier Transform
(which is the spatial frequency spectrum) in an N by N window centered
on each and every pixel in the image?  So that if you had a mega pixel
image, you'd have a million Fourier Transforms?  Seems like a strange
need.  What are you going to do with them?  Please explain further.

Perhaps not confusing, but I agree that it would be time consuming.

Nobody else but you said it would be time consuming.

The problem with DFT based 1D spectrograms such as here,

http://en.wikipedia.org/wiki/Spectrogram

is that they only provide useful information when the frequency
changes slowly compared to window length. In typical images, the
frequency changes rapidly over a length of a few pixels. However, the
definition of "time varying frequency" is pretty much determined by
the test method or application. As I recall, in the paper I
previously cited, various spectrogram methods were tested on a
sinusoid with a frequency that was a step function of time.
.

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