Characteristics of FFT of positive functions?

Image data is all positive.

So the FT of an image has a large DC component.

But, are there other characteristic properties of an all-positive
function? Similar, for example to the 'real-is-even' etc?

Chris
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Chris Bore
BORES Signal Processing
www.bores.com

Chris Bore wrote:
> Image data is all positive.
>
> So the FT of an image has a large DC component.
>
> But, are there other characteristic properties of an all-positive
> function? Similar, for example to the 'real-is-even' etc?

No, other than the general conjugate-symmetry that applies whenever you
transform real data.  The reason is that you can take *any* real array
and make it all positive by adding a sufficiently large constant to
every element of the array, and adding such a constant only affects the
DC element.

Cordially,
Steven G. Johnson