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premultiply alpha (if necessary) in affine

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This commit is contained in:
John Cupitt 2017-11-18 10:59:20 +00:00
parent fcec6d639b
commit e179e3b11f
2 changed files with 45 additions and 9 deletions
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2
cplusplus/examples/buffer.cpp
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@ -38,7 +38,7 @@ main( int argc, char **argv )
// load an image from a file
VImage im = VImage::new_from_file( argv[1],
VImage::option()->set( "access", "sequential-unbuffered" ) );
VImage::option()->set( "access", "sequential" ) );
printf( "loaded %d x %d pixel image from %s\n",
im.width(), im.height(), argv[1] );

52
libvips/resample/affine.c
View File

@ -86,6 +86,7 @@
* 7/11/17
* - add "background" parameter
* - better clipping means we have no jaggies on edges
* - premultiply alpha
*/
/*
@ -391,7 +392,7 @@ vips_affine_build( VipsObject *object )
VipsObjectClass *class = VIPS_OBJECT_GET_CLASS( object );
VipsResample *resample = VIPS_RESAMPLE( object );
VipsAffine *affine = (VipsAffine *) object;
VipsImage **t = (VipsImage **) vips_object_local_array( object, 4 );
VipsImage **t = (VipsImage **) vips_object_local_array( object, 7 );
VipsImage *in;
VipsDemandStyle hint;
@ -399,6 +400,11 @@ vips_affine_build( VipsObject *object )
int window_offset;
double edge;
/* TRUE if we've premultiplied and need to unpremultiply.
*/
gboolean have_premultiplied;
VipsBandFormat unpremultiplied_format;
if( VIPS_OBJECT_CLASS( vips_affine_parent_class )->build( object ) )
return( -1 );
@ -521,6 +527,23 @@ vips_affine_build( VipsObject *object )
affine->trn.idx -= 1;
affine->trn.idy -= 1;
/* If there's an alpha, we have to premultiply before resampling. See
* https://github.com/jcupitt/libvips/issues/291
*/
have_premultiplied = FALSE;
if( vips_image_hasalpha( in ) ) {
if( vips_premultiply( in, &t[3], NULL ) )
return( -1 );
have_premultiplied = TRUE;
/* vips_premultiply() makes a float image. When we
* vips_unpremultiply() below, we need to cast back to the
* pre-premultiply format.
*/
unpremultiplied_format = in->BandFmt;
in = t[3];
}
/* Normally SMALLTILE ... except if this is strictly a size
* up/down affine.
*/
@ -530,11 +553,12 @@ vips_affine_build( VipsObject *object )
else
hint = VIPS_DEMAND_STYLE_SMALLTILE;
if( vips_image_pipelinev( resample->out, hint, in, NULL ) )
t[4] = vips_image_new();
if( vips_image_pipelinev( t[4], hint, in, NULL ) )
return( -1 );
resample->out->Xsize = affine->trn.oarea.width;
resample->out->Ysize = affine->trn.oarea.height;
t[4]->Xsize = affine->trn.oarea.width;
t[4]->Ysize = affine->trn.oarea.height;
#ifdef DEBUG
printf( "vips_affine_build: transform: " );
@ -544,20 +568,32 @@ vips_affine_build( VipsObject *object )
printf( " input image width = %d, height = %d\n",
in->Xsize, in->Ysize );
printf( " output image width = %d, height = %d\n",
resample->out->Xsize, resample->out->Ysize );
t[4]->Xsize, t[4]->Ysize );
#endif /*DEBUG*/
/* Generate!
*/
if( vips_image_generate( resample->out,
if( vips_image_generate( t[4],
vips_start_one, vips_affine_gen, vips_stop_one,
in, affine ) )
return( -1 );
/* Finally: can now set Xoffset/Yoffset.
*/
resample->out->Xoffset = affine->trn.odx - affine->trn.oarea.left;
resample->out->Yoffset = affine->trn.ody - affine->trn.oarea.top;
t[4]->Xoffset = affine->trn.odx - affine->trn.oarea.left;
t[4]->Yoffset = affine->trn.ody - affine->trn.oarea.top;
in = t[4];
if( have_premultiplied ) {
if( vips_unpremultiply( in, &t[5], NULL ) ||
vips_cast( t[5], &t[6], unpremultiplied_format, NULL ) )
return( -1 );
in = t[6];
}
if( vips_image_write( in, resample->out ) )
return( -1 );
return( 0 );
}