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remove a 0.5 pixel shift from triangle 

lines up with cubic and lanczos now
This commit is contained in:
John Cupitt 2017-10-16 09:38:04 +01:00
parent 53119250cc
commit 0767e4f4c9
1 changed files with 31 additions and 31 deletions
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62
libvips/resample/templates.h
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@ -311,6 +311,37 @@ calculate_coefficients_catmull( double c[4], const double x )
c[2] = cthr;
}
/* Given an x in [0,1] (we can have x == 1 when building tables),
* calculate c0 .. c(@shrink + 1), the triangle coefficients. This is called
* from the interpolator as well as from the table builder.
*/
static void inline
calculate_coefficients_triangle( double *c, const double shrink, const double x )
{
/* Needs to be in sync with vips_reduce_get_points().
*/
const int n_points = rint( 2 * shrink ) + 1;
int i;
double sum;
sum = 0;
for( i = 0; i < n_points; i++ ) {
double xp = (i - (shrink - 0.5) - x) / shrink;
double l;
l = 1.0 - VIPS_FABS( xp );
l = VIPS_MAX( 0.0, l );
c[i] = l;
sum += l;
}
for( i = 0; i < n_points; i++ )
c[i] /= sum;
}
/* Calculate a catmull kernel for shrinking.
*/
static void inline
@ -397,37 +428,6 @@ calculate_coefficients_lanczos( double *c,
c[i] /= sum;
}
/* Given an x in [0,1] (we can have x == 1 when building tables),
* calculate c0 .. c(@shrink + 1), the triangle coefficients. This is called
* from the interpolator as well as from the table builder.
*/
static void inline
calculate_coefficients_triangle( double *c, const double shrink, const double x )
{
/* Needs to be in sync with vips_reduce_get_points().
*/
const int n_points = rint( 2 * shrink ) + 1;
int i;
double sum;
sum = 0;
for( i = 0; i < n_points; i++ ) {
double xp = (i - (shrink - 1) - x) / shrink;
double l;
l = 1.0 - VIPS_FABS( xp );
l = VIPS_MAX( 0.0, l );
c[i] = l;
sum += l;
}
for( i = 0; i < n_points; i++ )
c[i] /= sum;
}
/* Our inner loop for resampling with a convolution. Operate on elements of
* type T, gather results in an intermediate of type IT.
*/