Re:

SteveSmith wrote:
Hi Michel,
Let me suggest that you are thinking about this problem in a fundamentally
wrong way. You have image 1, and want to create image 2 that is a
different size. Further, you want image 2 to be similar to image 1 "in
some sense." In other words, the two images cannot be identical, so
you need to define a criterion for measuring the "correctness" of
image 2. The method you are trying (frequency band filtering with
decimation/interpolation) achieves this “in the sense” that the two
images have similar frequency spectra.

Here’s the catch. The information you are dealing with is encoded in
the spatial domain, not the frequency domain. That is, you are interested
in the spatial patterns, their edges, their positions, their amplitudes,
and so on. Accordingly, you want image 2 to be similar to image 1 in
“some sense” that is related to the spatial domain. This is in
contrast to, for example, an audio signal that is primarily encoded in the
frequency domain.

The problems you are seeing are a direct result of trying to manipulate
the data in the wrong domain. For instance, when you perform simple
filtering in the frequency domain, you create unpredictable artifacts in
the spatial domain. Instead, ask yourself this, "how should a pixel in
image 1 affect each pixel in image 2?" For instance, should an isolated
bright pixel in the original image be converted to a single bright pixel in
the new image?

Steve,

It's clear why you write the books. I was trying to formulate the words to get across just what you wrote above when I saw it. You got to the point directly and simply compared to what I was paring down. I would probably have gotten there eventually, but not as well as you did.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
.

Relevant Pages

  • Re:
    ... The method you are trying (frequency band filtering with ... the spatial domain, not the frequency domain. ... bright pixel in the original image be converted to a single bright pixel in ...
    (comp.dsp)
  • Re: "Good" FIRs with no negative parts
    ... the spatial domain, not the frequency domain. ... "some sense" that is related to the spatial domain. ... bright pixel in the original image be converted to a single bright pixel in ... which imply that the image will look softer, as the single bright ...
    (comp.dsp)
  • "Good" FIRs with no negative parts
    ... the spatial domain, not the frequency domain. ... "some sense" that is related to the spatial domain. ... bright pixel in the original image be converted to a single bright pixel in ... which imply that the image will look softer, as the single bright ...
    (comp.dsp)
  • Re: Convolution in frequency (Fourier) space
    ... If the transformation from spatial to frequency back to spatial domain ... doing a tranform to frequency domain, ... convolve each of the resulting matrices with a given kernel (in ... Convolution in the spatial domain is equivalent to multiplication in the frequency ...
    (sci.image.processing)
  • Re: Creating noise in the frequency domain?
    ... filtered in the frequency domain and then transformed back to the ... So, basically, I skip the step of transforming into the frequency ... What is the frequency-domain-equivalent distribution of complex ... numbers to *Gaussian* noise in the spatial domain? ...
    (sci.image.processing)