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From: roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson)
Newsgroups: comp.soft-sys.matlab
Subject: Re: data compression
Date: Fri, 16 May 2008 20:17:24 +0000 (UTC)
Organization: National Research Council Canada - Conseil national de rechereches Canada
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In article <g0gl00$nhs$1@fred.mathworks.com>,
Ahmed  <mogwari2000@yahoo.com> wrote:
>I have a large database that containing images.  Every 
>image is described with a matrix (X) which has two vectors 
>one vector is the horizontal projection and the other 
>vector is vertical projection of the image. These vectors 
>have the same length (d). For example let d=512, this 
>means that the size of (X) = 512x2.

I am confused by your reference to "horizontal" and "vertical"
"projection". Your wording could mean that the images can be
reconstructed perfectly by that dx2 vector, such as would be the
case if the "image" was a simple X/Y plot and the two vectors
were the X and Y coordinates.

Looking at your later posting about signatures and so on, I am now
wondering if the "projections" are some kind of signal analysis
of the image, with the analysis applied once horizontally and
once vertically, and the two vectors then contain the coefficients
appropriate for each direction? Or do you mean "horizontal projection"
in the linear algebra sense, sort of the "shadow" that would be
cast by the image if you pretended it was solid and shone a light on it?
-- 
  "All human knowledge takes the form of interpretation."
                                              -- Walter Benjamin