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From: div bansal on 7 Mar 2010 10:46
I would llike to know the heurisitic which is used to find the value of the knee point during image compression in the eigen value plot. It will be of great help.

Thanks and Regards
Div
From: Greg Heath on 7 Mar 2010 12:03
On Mar 7, 10:46 am, "div bansal" <divay.ban...(a)gmail.com> wrote:
> I would llike to know the heurisitic which is used to find the value of the knee point during image compression in the eigen value plot. It will be of great help.
>
> Thanks and Regards
> Div

The knee is located at a point where the radius of curvature.
is a local minimum. For a curve y = f(x) the curvature is

k = y''/(1+(y')^2)^(3/2).

Just repace the derivatives with finite differences.

Hope this helps.

Greg
From: Greg Heath on 7 Mar 2010 12:15
On Mar 7, 10:46 am, "div bansal" <divay.ban...(a)gmail.com> wrote:
> I would llike to know the heurisitic which is used to find the value of the knee point during image compression in the eigen value plot. It will be of great help.
>
> Thanks and Regards
> Div

Rather than search for the knee, I usually set a threshold,
say 0.99, or 0.95 and keep m of n eigenvalues when

T(m-1) < 0.99 *T(n) <= T(m)

where

T(m) = sum(i=1:m){lambda(i)}

Hope this helps.

Greg
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