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fix centre sampling for non-int nearest upscale

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we were not disabling the input offset for NEAREST, whcih is always
centre

thanks edwjusti

see https://github.com/lovell/sharp/issues/1479
This commit is contained in:
John Cupitt 2018-12-03 17:13:57 +00:00
parent ee4d1d7c22
commit f5d76b42fc
1 changed files with 8 additions and 2 deletions
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10
libvips/resample/resize.c
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@ -28,6 +28,9 @@
* - make LINEAR and CUBIC adaptive * - make LINEAR and CUBIC adaptive
* 25/11/17 * 25/11/17
* - deprecate --centre ... it's now always on, thanks tback * - deprecate --centre ... it's now always on, thanks tback
* 3/12/18 [edwjusti]
* - disable the centre sampling offset for nearest upscale, since the
* affine nearest interpolator is always centre
*/ */
/* /*
@ -241,9 +244,12 @@ vips_resize_build( VipsObject *object )
vips_resize_interpolate( resize->kernel ); vips_resize_interpolate( resize->kernel );
/* Input displacement. For centre sampling, shift by 0.5 down /* Input displacement. For centre sampling, shift by 0.5 down
* and right. * and right. Except if this is nearest, which is always
* centre.
*/ */
const double id = 0.5; const double id =
resize->kernel == VIPS_KERNEL_NEAREST ?
0.0 : 0.5;
VipsInterpolate *interpolate; VipsInterpolate *interpolate;