RE: Dithering (was Re: FWD [forteana] [More steganography] Hidden webcodes could be linked to Bin Laden)

From: Harvey Newstrom (
Date: Fri Oct 12 2001 - 07:52:16 MDT

James Rogers wrote,
> On 10/11/01 9:35 AM, "Harvey Newstrom" <> wrote:
> >
> > Also, counter-intuitively, adding noise actually makes it *easier* to
> > eliminate the noise. The more noise there is, the more statistically
> > predictable it becomes. Statistical analysis works better the
> more sample
> > you have. Lots of static over a longer period of time actually makes it
> > easier to eliminate the static.
> This isn't quite right. Adding noise increases the noise floor
> in exchange
> for reducing quantization distortion. The improvement in signal
> quality is
> more apparent than real. The human brain has an easier time
> rejecting noise
> than correcting quantization distortion, so adding noise to mask the
> distortion is a cheap solution.

Your comments are quite right when addressing the ability of the human brain
to perceive the distortions. However, I was discussing a computer's ability
to statistically analyze the low-order bits that are imperceptible to

Human brains will indeed ignore additional noise because it tends to mask
this out. The more noise, the closer it falls to a predictable curve, and
the easier it is to detect and ignore. The human brain does this
automatically, and computers can be programmed to do this as well. The
additional noise becomes filtered out by the human brain exactly because it
becomes easier to detect and isolate.

Harvey Newstrom <>
Principal Security Consultant, Newstaff Inc. <>
Board of Directors, Extropy Institute <>
Cofounder, Pro-Act <>

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