[svlug] compare image

[Karen Shaeffer]

On Fri, Aug 04, 2000 at 07:47:25PM -0700, kmself at ix.netcom.com wrote:
> On Fri, Aug 04, 2000 at 12:05:49PM -0700, Will Francis wrote:
> > 
> Nothing specific, but this is a fundamental concept behind most
> web-based streaming video, as it's a lot easier to transfer changing
> content and leaving the static stuff alone.  I'd start digging there.
> 
> -- 
> Karsten M. Self <kmself at ix.netcom.com>     http://www.netcom.com/~kmself

Hi Karsten,

Yes, this is a basic premise of the generalized mathematics
of image and video compression. (e.g., JPEG or MPEG) An excellent
general reference is:

Arun N. Netravali and Barry G. Haskell; Digital Pictures: Representation
and Compression; Plenum Press, 1988 ATT Bell Labs

There is a second edition in print.

If you look into these mathematics, you'll realize one must be clear
about defining what is meant by *difference*. It's all about thresholds
and difference algorithms. By difference one might mean average values
for luminance or some windowed metric, etc. More likely, Will is most
interested in detecting changes in image objects. In that case, the
mathematics must detect temporal variances in edges. Here edges are
defined as contiguous lines of high contrast.

As Will suggested, this genre of application *ought* to exist. If not,
I'm sure someone will have a wonderful time writing it. This is all
very interesting stuff--interesting algorithms and mathematics.

c,
-- 
 Karen Shaeffer
 Neuralscape; Santa Cruz, Ca. 95060
 shaeffer at neuralscape.com  http://www.neuralscape.com