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Path: utzoo!mnetor!seismo!ut-sally!im4u!milano!begeman
From: begeman@milano.UUCP
Newsgroups: comp.graphics
Subject: Re: Intelligent scaling of bit-mapped graphics (Help!)
Message-ID: <3385@milano.UUCP>
Date: Thu, 15-Jan-87 13:05:55 EST
Article-I.D.: milano.3385
Posted: Thu Jan 15 13:05:55 1987
Date-Received: Fri, 16-Jan-87 01:44:24 EST
References: <2872@gitpyr.gatech.EDU> <2406@well.UUCP>
Sender: begeman@milano.UUCP
Organization: MCC, Austin, TX
Lines: 37
Summary: Surface fitting

> In article <2872@gitpyr.gatech.EDU> dave@gitpyr.gatech.EDU (David Corbin) writes:
> >I am looking for information (programs, algorithms, references to texts)
> >on how to scale a bit-mapped image from one resolution to another, in an
> >intelligent manner....

Ok, here goes.  There may be cheaper ways, but in my book there's
one *right* way.  What you have is an interpolation problem.  Imagine
your image (1st resolution) as a set of sampled data values.  What
you want is to derive other data values which are "in between" these.

What you need to do is find a surface-fitting algorithm.  You will
feed it your data as (X, Y, Z==pixel_value) tuples.  The algorithm
will fit a surface to the data.  Then you can use the surface to
compute New_Z = f(New_X, New_Y) where f is the interpolation function
as applied to the surface.

This software falls into the domain of Numerical Analysis.  I don't
know of any public domain code which I can point you to, but I know
that lots of PD NA software *does* exist.  

By the way, there will be a number of different surface-fitting
algorithms to choose from - usually differing in the order of the
polynomials used and your ability to "tension" the surface to remove
any spikey anomalies which the mathematical representation of your
original data may have introduced.  Hit your local Numerical Analyst
for guidance here.

Good luck!
 
-------
	Of all the things I've lost, I miss my mind the most.

Michael L. Begeman              Microelectronics and Computer Technology Corp
Software Technology Program     Austin (where the sun always shines) Texas

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