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better handling of "nearest" in resize 

we now use vips_subsample() for this case
This commit is contained in:
John Cupitt 2020-06-12 12:03:15 +01:00
parent 675c72b07f
commit 4469afaeb0
1 changed files with 34 additions and 55 deletions
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63
libvips/resample/resize.c
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@ -33,6 +33,8 @@
* affine nearest interpolator is always centre
* 7/7/19 [lovell]
* - don't let either axis drop below 1px
* 12/7/20
* - much better handling of "nearest"
*/
/*
@ -105,45 +107,6 @@ typedef VipsResampleClass VipsResizeClass;
G_DEFINE_TYPE( VipsResize, vips_resize, VIPS_TYPE_RESAMPLE );
/* How much of a scale should be by an integer shrink factor?
*
* This depends on the scale and the kernel we will use for residual resizing.
* For upsizing and nearest-neighbour downsize, we want no shrinking.
*
* The others are adaptive: the size of the kernel changes with the shrink
* factor. We will get the best quality (but be the slowest) if we let
* reduce do all the work. Leave it the final 200 - 300% to do as a compromise
* for efficiency.
*
* FIXME: this is rather ugly. Kernel should be a class and this info should be
* stored in there.
*/
static int
vips_resize_int_shrink( VipsResize *resize, double scale )
{
int shrink;
if( scale > 1.0 )
shrink = 1;
else
switch( resize->kernel ) {
case VIPS_KERNEL_NEAREST:
shrink = 1;
break;
case VIPS_KERNEL_LINEAR:
case VIPS_KERNEL_CUBIC:
case VIPS_KERNEL_MITCHELL:
case VIPS_KERNEL_LANCZOS2:
case VIPS_KERNEL_LANCZOS3:
default:
shrink = VIPS_MAX( 1, VIPS_FLOOR( 1.0 / (scale * 2) ) );
break;
}
return( shrink );
}
/* Suggest a VipsInterpolate which corresponds to a VipsKernel. We use
* this to pick a thing for affine().
*/
@ -192,10 +155,10 @@ vips_resize_build( VipsObject *object )
else
vscale = resize->scale;
/* The int part of our scale.
/* The int part of our scale. Leave the final 200 - 300% to reduce.
*/
int_hshrink = vips_resize_int_shrink( resize, hscale );
int_vshrink = vips_resize_int_shrink( resize, vscale );
int_hshrink = VIPS_MAX( 1, VIPS_FLOOR( 1.0 / (hscale * 2) ) );
int_vshrink = VIPS_MAX( 1, VIPS_FLOOR( 1.0 / (vscale * 2) ) );
/* Unpack for processing.
*/
@ -203,6 +166,21 @@ vips_resize_build( VipsObject *object )
return( -1 );
in = t[5];
if( resize->kernel == VIPS_KERNEL_NEAREST ) {
if( int_vshrink > 1 ||
int_hshrink > 1 ) {
g_info( "subsample by %d, %d",
int_hshrink, int_vshrink );
if( vips_subsample( in, &t[0],
int_hshrink, int_vshrink, NULL ) )
return( -1 );
in = t[0];
hscale *= int_hshrink;
vscale *= int_vshrink;
}
}
else {
if( int_vshrink > 1 ) {
g_info( "shrinkv by %d", int_vshrink );
if( vips_shrinkv( in, &t[0], int_vshrink, NULL ) )
@ -220,6 +198,7 @@ vips_resize_build( VipsObject *object )
hscale *= int_hshrink;
}
}
/* Don't let either axis drop below 1 px.
*/