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smarter heif thumbnail selection in `thumbnail` 

We were checking for thumbnail width and height > target width and
height, but of course we can have one of target width or height very
large if we are leaving that axis to float in size.

Instead, calculate a shrink from the heif thumbnail size and see if that is
>= 1.0, ie. we can generate output without upsizing.
This commit is contained in:
John Cupitt 2019-09-30 14:34:11 +01:00
parent 4f1e57c040
commit a92f0ed504
1 changed files with 12 additions and 10 deletions
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22
libvips/resample/thumbnail.c
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@ -24,6 +24,8 @@
* - support multi-page (animated) images
* 27/8/19 kleisauke
* - prevent over-pre-shrink in thumbnail
* 30/9/19
* - smarter heif thumbnail selection
*/
/*
@ -379,9 +381,7 @@ vips_thumbnail_calculate_common_shrink( VipsThumbnail *thumbnail,
/* We don't want to shrink so much that we send an axis to 0.
*/
if( shrink > thumbnail->input_width ||
shrink > thumbnail->input_height )
shrink = 1.0;
shrink = VIPS_MIN( shrink, VIPS_MIN( width, height ) );
return( shrink );
}
@ -489,17 +489,19 @@ vips_thumbnail_open( VipsThumbnail *thumbnail )
factor = vips_thumbnail_calculate_common_shrink( thumbnail,
thumbnail->input_width,
thumbnail->page_height );
if( vips_isprefix( "VipsForeignLoadHeif", thumbnail->loader ) ) {
else if( vips_isprefix( "VipsForeignLoadHeif", thumbnail->loader ) ) {
/* 'factor' is a gboolean which enables thumbnail load instead
* of image load.
*
* Use the thumbnail if it's larger than our target.
* Use the thumbnail if, by using it, we could get a factor >=
* 1.0, ie. we would not need to expand the thumbnail.
*/
if( thumbnail->heif_thumbnail_width >= thumbnail->width &&
thumbnail->heif_thumbnail_height >= thumbnail->height )
factor = 1.0;
else
factor = 0.0;
double shrink_factor = vips_thumbnail_calculate_common_shrink(
thumbnail,
thumbnail->heif_thumbnail_width,
thumbnail->heif_thumbnail_height );
factor = shrink_factor >= 1.0 ? 1 : 0;
}
g_info( "loading with factor %g pre-shrink", factor );