Re: Can gray image’ pixel value be negative?

"John D'Errico" <woodchips@xxxxxxxxxxxxxxxx> wrote in message <gb7rtl$1ub$1@xxxxxxxxxxxxxxxxxx>...
lijing <verylijing@xxxxxxx> wrote in message <1aeb3683-1e4d-4b5f-ad51-116d3d71527a@xxxxxxxxxxxxxxxxxxxxxxxxxxx>...
Want to normalize an gray image to zero mean and unit variance, but
now I wonder could a gray image=92 pixel value be negative? I have never
seen. Could you give some explanation?
Thank you for your attention! Thank you for your replay!

A zero mean would imply that some values are
positive and some negative. This is inherent in
the definition of the mean, unless all of the
values are identically zero.

So why are you even remotely surprised at this
result?

John

Once you have undertaken a zero mean transformation on your greyscale image, it is no longer an image in the conventional sense, it is merely a two dimensional numerical matrix containing both positive and negative values, which - if you have done your arithmetic correctly - should sum to zero.

Regards

Dave Robinson
.

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