From: "Michel Chabroux" <michel@strategicsol.com>
Subject: Re: Bilinear Interpolation
Date: 23 May 2000 00:00:00 GMT
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References: <392A7E8C.164BD689@cad.ntu-kpi.kiev.ua>
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"meloman" <meloman@cad.ntu-kpi.kiev.ua> wrote in message
news:392A7E8C.164BD689@cad.ntu-kpi.kiev.ua...
> Can someone tell me about subj?

Well, not that much complicate... Here's what to do at each pixel once
you've the real mapping coordinates (let's say u and v):
f0=(1-frac(u)*(1-frac(v))
f1=frac(u)*(1-frac(v))
f2=frc(u)*frac(v)
f3=(1-frac(u))*frac(v)

where frac(t) is the fractionnal part of t.

Then you'll use the colors are the 4 surrounding points P0, P1, P2 and P3 as
shown below :

P0          P1
  +--------+
  |   .    |
  |...X....|
  |   .    |
  |   .    |
  +--------+
P3          P2

The "bilinear filtered" color of your point (marked by the X) will be :

R=R0*f0+R1*f1+R2*f2+R3*f3
G=G0*f0+G1*f1+G2*f2+G3*f3
B=B0*f0+B1*f1+B2*f2+B3*f3

Voila ! Hope it'll help.

Michel