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interpolate_bicubic.c
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interpolate_bicubic.c
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#include "header.h"
#include "proto.h"
double interpolate_bicubic(
double *I,
double x,
double y,
int xdim,
int ydim
)
/*
Interpolate the value of the intensity at (x,y)
*/
/*
x is assumed to be between 0 and (xdim-1)
0 <= x <= (xdim-1)
y is assumed to be between 0 and (ydim-1)
0 <= y <= (ydim-1)
*/
{
int i0;
int i1;
int i2;
int i3;
int j0;
int j1;
int j2;
int j3;
double p00;
double p01;
double p02;
double p03;
double p10;
double p11;
double p12;
double p13;
double p20;
double p21;
double p22;
double p23;
double p30;
double p31;
double p32;
double p33;
double q0;
double q1;
double q2;
double q3;
double f;
/*
Recall that x is the horizontal coordinate
going from left to right
Recall that y is the vertical coordinate
going from top to bottom
It is assumed that 0 <= x <= (xdim-1)
It is assumed that 0 <= y <= (ydim-1)
*/
if ( !(x >= 0) )
er9b_error_handler("er9b_downsample_image");
if ( !(x <= (xdim-1)) )
er9b_error_handler("er9b_downsample_image");
if ( !(y >= 0) )
er9b_error_handler("er9b_downsample_image");
if ( !(y <= (ydim-1)) )
er9b_error_handler("er9b_downsample_image");
/*
i is gonna represent the row
j is gonna represent the column
*/
/*
Let's gather the 4x4 matrix of points
Recall that (x,y) is supposed to lie somewhere
in the p11,p12,p21,p22 square
*/
i1= (int)y;
if ( i1 == (ydim-1) )
i1--;
i0= i1-1;
i2= i1+1;
i3= i2+1;
j1= (int)x;
if ( j1 == (xdim-1) )
j1--;
j0= j1-1;
j2= j1+1;
j3= j2+1;
/*
Repeat the point if out of bounds
*/
if ( i0 == -1 )
i0= i1;
if ( i3 == ydim )
i3= i2;
if ( j0 == -1 )
j0= j1;
if ( j3 == xdim )
j3= j2;
/*
Row 0
*/
p00= I[xdim*i0+j0];
p01= I[xdim*i0+j1];
p02= I[xdim*i0+j2];
p03= I[xdim*i0+j3];
/*
Row 1
*/
p10= I[xdim*i1+j0];
p11= I[xdim*i1+j1];
p12= I[xdim*i1+j2];
p13= I[xdim*i1+j3];
/*
Row 2
*/
p20= I[xdim*i2+j0];
p21= I[xdim*i2+j1];
p22= I[xdim*i2+j2];
p23= I[xdim*i2+j3];
/*
Row 3
*/
p30= I[xdim*i3+j0];
p31= I[xdim*i3+j1];
p32= I[xdim*i3+j2];
p33= I[xdim*i3+j3];
/*
Let's first interpolate along the columns
*/
/*
Column 0
*/
q0= interpolate_cubic(
p00,
p10,
p20,
p30,
y-i1
);
/*
Column 1
*/
q1= interpolate_cubic(
p01,
p11,
p21,
p31,
y-i1
);
/*
Column 2
*/
q2= interpolate_cubic(
p02,
p12,
p22,
p32,
y-i1
);
/*
Column 3
*/
q3= interpolate_cubic(
p03,
p13,
p23,
p33,
y-i1
);
/*
Finally, interpolate horizontally
*/
f= interpolate_cubic(
q0,
q1,
q2,
q3,
x-j1
);
return f;
}