Path: utzoo!attcan!uunet!nih-csl!lhc!adm!cmcl2!yale!cs.utexas.edu!usc!apple!bionet!agate!shelby!morrow.stanford.edu!pangea.Stanford.EDU!rick
From: rick@pangea.Stanford.EDU (Rick Ottolini)
Newsgroups: comp.graphics
Subject: Re: Fast Image Scaling
Message-ID: <1990Oct26.011905.16187@morrow.stanford.edu>
Date: 26 Oct 90 01:19:05 GMT
References: <A1346770260@syntel.syntel.mn.org>
Sender: news@morrow.stanford.edu (UNIX News Service)
Organization: Stanford Univ. Earth Sciences
Lines: 30

In article <A1346770260@syntel.syntel.mn.org> dal@syntel.syntel.mn.org (Dale A. Schumacher) writes:
>The following pseudo-code is from a rough draft of a paper I'm preparing
>for inclusion in Graphics Gems '91.  It is in the public domain.
>
>
>src_x_size:	integer;
>src_y_size:	integer;
>source:		array[0..src_x_size-1] of array[0..src_y_size-1] of pixel;
>dst_x_size:	integer;
>dst_y_size:	integer;
>destination:	array[0..dst_x_size-1] of array[0..dst_y_size-1] of pixel;
>sx, sy, dx, dy:	integer;
>
>begin
>	dx <- 0;
>	dy <- 0;
>	while dy < dst_y_size do
>		sy <- ((dy * src_y_size) / dst_y_size);
>		while dx < dst_x_size do
>			sx <- ((dx * src_x_size) / dst_x_size);
>			destination[dx][dy] <- source[sx][sy];
>		endloop;
>	endloop;
>end;

Two problems (at least):
(1) When shrinking the high freqyency components of an image must be removed
or else aliasing will result.  A fast way to do this is to smooth with a
(rectangular) window the degree of compression.
(2) Pre-computing each axis of of sx and sy is even faster than above.