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Add alpha_q(uality) webpsave option, fix Q init 

This allows to control the fidelity of the alpha channel by allowing
webp to reduce the number of palette entries from 256 at alpha_q=100
to 2 at alpha_q=0. This is most useful with cutout pictures where
something like alpha_q=30 or around 8 levels is usually sufficient
for smooth outlines.

For some reason webp->Q was intiailized to 80 even though the Q option
and libwebp use 75 by default. This was never used, so it's just to
avoid confusion about what default is used.
This commit is contained in:
Felix Bünemann 2016-04-23 02:41:59 +02:00
parent c107066c4e
commit 0a25f6efca
4 changed files with 33 additions and 11 deletions
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2
libvips/foreign/foreign.c
View File

@ -2462,6 +2462,7 @@ vips_webpload_buffer( void *buf, size_t len, VipsImage **out, ... )
* @preset: #VipsForeignWebpPreset choose lossy compression preset
* @smart_subsample: enables high quality chroma subsampling
* @near_lossless: use preprocessing in lossless mode (controlled by Q)
* @alpha_q: set alpha quality in lossless mode
*
* See also: vips_webpload(), vips_image_write_to_file().
*
@ -2494,6 +2495,7 @@ vips_webpsave( VipsImage *in, const char *filename, ... )
* @preset: #VipsForeignWebpPreset choose lossy compression preset
* @smart_subsample: enables high quality chroma subsampling
* @near_lossless: use preprocessing in lossless mode (controlled by Q)
* @alpha_q: set alpha quality in lossless mode
*
* See also: vips_webpsave().
*

14
libvips/foreign/vips2webp.c
View File

@ -85,7 +85,8 @@ get_preset( VipsForeignWebpPreset preset )
static int
write_webp( WebPPicture *pic, VipsImage *in,
int Q, gboolean lossless, VipsForeignWebpPreset preset,
gboolean smart_subsample, gboolean near_lossless )
gboolean smart_subsample, gboolean near_lossless,
int alpha_q )
{
VipsImage *memory;
WebPConfig config;
@ -102,6 +103,7 @@ write_webp( WebPPicture *pic, VipsImage *in,
config.preprocessing |= 4;
if( near_lossless )
config.near_lossless = Q;
config.alpha_quality = alpha_q;
if( !WebPValidateConfig(&config) ) {
vips_error( "vips2webp",
@ -147,7 +149,8 @@ write_webp( WebPPicture *pic, VipsImage *in,
int
vips__webp_write_file( VipsImage *in, const char *filename,
int Q, gboolean lossless, VipsForeignWebpPreset preset,
gboolean smart_subsample, gboolean near_lossless )
gboolean smart_subsample, gboolean near_lossless,
int alpha_q )
{
WebPPicture pic;
WebPMemoryWriter writer;
@ -164,7 +167,7 @@ vips__webp_write_file( VipsImage *in, const char *filename,
pic.custom_ptr = &writer;
if( write_webp( &pic, in, Q, lossless, preset, smart_subsample,
near_lossless ) ) {
near_lossless, alpha_q ) ) {
WebPPictureFree( &pic );
WebPMemoryWriterClear( &writer );
return -1;
@ -192,7 +195,8 @@ vips__webp_write_file( VipsImage *in, const char *filename,
int
vips__webp_write_buffer( VipsImage *in, void **obuf, size_t *olen,
int Q, gboolean lossless, VipsForeignWebpPreset preset,
gboolean smart_subsample, gboolean near_lossless )
gboolean smart_subsample, gboolean near_lossless,
int alpha_q )
{
WebPPicture pic;
WebPMemoryWriter writer;
@ -209,7 +213,7 @@ vips__webp_write_buffer( VipsImage *in, void **obuf, size_t *olen,
pic.custom_ptr = &writer;
if( write_webp( &pic, in, Q, lossless, preset, smart_subsample,
near_lossless) ) {
near_lossless, alpha_q ) ) {
WebPPictureFree( &pic );
WebPMemoryWriterClear( &writer );
return -1;

6
libvips/foreign/webp.h
View File

@ -50,10 +50,12 @@ int vips__webp_read_buffer( const void *buf, size_t len,
int vips__webp_write_file( VipsImage *out, const char *filename,
int Q, gboolean lossless, VipsForeignWebpPreset preset,
gboolean smart_subsample, gboolean near_lossless );
gboolean smart_subsample, gboolean near_lossless,
int alpha_q );
int vips__webp_write_buffer( VipsImage *out, void **buf, size_t *len,
int Q, gboolean lossless, VipsForeignWebpPreset preset,
gboolean smart_subsample, gboolean near_lossless );
gboolean smart_subsample, gboolean near_lossless,
int alpha_q );
#ifdef __cplusplus
}

22
libvips/foreign/webpsave.c
View File

@ -72,6 +72,10 @@ typedef struct _VipsForeignSaveWebp {
*/
gboolean near_lossless;
/* Alpha quality.
*/
int alpha_q;
} VipsForeignSaveWebp;
typedef VipsForeignSaveClass VipsForeignSaveWebpClass;
@ -143,12 +147,19 @@ vips_foreign_save_webp_class_init( VipsForeignSaveWebpClass *class )
G_STRUCT_OFFSET( VipsForeignSaveWebp, near_lossless ),
FALSE );
VIPS_ARG_INT( class, "alpha_q", 15,
_( "Alpha quality" ),
_( "Change alpha plane fidelity for lossy compression" ),
VIPS_ARGUMENT_OPTIONAL_INPUT,
G_STRUCT_OFFSET( VipsForeignSaveWebp, alpha_q ),
0, 100, 100 );
}
static void
vips_foreign_save_webp_init( VipsForeignSaveWebp *webp )
{
webp->Q = 80;
webp->Q = 75;
}
typedef struct _VipsForeignSaveWebpFile {
@ -178,7 +189,8 @@ vips_foreign_save_webp_file_build( VipsObject *object )
if( vips__webp_write_file( save->ready, file->filename,
webp->Q, webp->lossless, webp->preset,
webp->smart_subsample, webp->near_lossless ) )
webp->smart_subsample, webp->near_lossless,
webp->alpha_q ) )
return( -1 );
return( 0 );
@ -241,7 +253,8 @@ vips_foreign_save_webp_buffer_build( VipsObject *object )
if( vips__webp_write_buffer( save->ready, &obuf, &olen,
webp->Q, webp->lossless, webp->preset,
webp->smart_subsample, webp->near_lossless ) )
webp->smart_subsample, webp->near_lossless,
webp->alpha_q ) )
return( -1 );
blob = vips_blob_new( (VipsCallbackFn) vips_free, obuf, olen );
@ -303,7 +316,8 @@ vips_foreign_save_webp_mime_build( VipsObject *object )
if( vips__webp_write_buffer( save->ready, &obuf, &olen,
webp->Q, webp->lossless, webp->preset,
webp->smart_subsample, webp->near_lossless ) )
webp->smart_subsample, webp->near_lossless,
webp->alpha_q ) )
return( -1 );
printf( "Content-length: %zu\r\n", olen );