Add webpsave near_lossless support, fix Q range

The near_lossless option allows to enable preprocessing for the lossless
mode. This is a boolean instead of an int, because the amount of
preprocessing is controlled using the Q factor parameter which is
otherwise unused in lossless mode. This allows to re-use the quality
setting in existing tools.

libvips/foreign/foreign.c

@@ -2461,6 +2461,7 @@ vips_webpload_buffer( void *buf, size_t len, VipsImage **out, ... )
  * @lossless: enables lossless compression
  * @preset: #VipsForeignWebpPreset choose lossy compression preset
  * @smart_subsample: enables high quality chroma subsampling
+ * @near_lossless: use preprocessing in lossless mode (controlled by Q)
  *
  * See also: vips_webpload(), vips_image_write_to_file().
  *
@@ -2492,6 +2493,7 @@ vips_webpsave( VipsImage *in, const char *filename, ... )
  * @lossless: enables lossless compression
  * @preset: #VipsForeignWebpPreset choose lossy compression preset
  * @smart_subsample: enables high quality chroma subsampling
+ * @near_lossless: use preprocessing in lossless mode (controlled by Q)
  *
  * See also: vips_webpsave().
  *

libvips/foreign/vips2webp.c

@@ -85,7 +85,7 @@ get_preset( VipsForeignWebpPreset preset )
 static int
 write_webp( WebPPicture *pic, VipsImage *in,
 	int Q, gboolean lossless, VipsForeignWebpPreset preset,
-	gboolean smart_subsample )
+	gboolean smart_subsample, gboolean near_lossless )
 {
 	VipsImage *memory;
 	WebPConfig config;
@@ -97,9 +97,11 @@ write_webp( WebPPicture *pic, VipsImage *in,
 		return( -1 );
 	}
 
-	config.lossless = lossless;
+	config.lossless = lossless || near_lossless;
 	if( smart_subsample )
 		config.preprocessing |= 4;
+	if( near_lossless )
+		config.near_lossless = Q;
 
 	if( !WebPValidateConfig(&config) ) {
 		vips_error( "vips2webp",
@@ -113,7 +115,7 @@ write_webp( WebPPicture *pic, VipsImage *in,
 	/* Smart subsampling requires use_argb because
 	 * it is applied during RGB to YUV conversion.
 	 */
-	pic->use_argb = lossless || smart_subsample;
+	pic->use_argb = lossless || near_lossless || smart_subsample;
 	pic->width = memory->Xsize;
 	pic->height = memory->Ysize;
 
@@ -145,7 +147,7 @@ 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 smart_subsample, gboolean near_lossless )
 {
 	WebPPicture pic;
 	WebPMemoryWriter writer;
@@ -161,7 +163,8 @@ vips__webp_write_file( VipsImage *in, const char *filename,
 	pic.writer = WebPMemoryWrite;
 	pic.custom_ptr = &writer;
 
-	if( write_webp( &pic, in, Q, lossless, preset, smart_subsample ) ) {
+	if( write_webp( &pic, in, Q, lossless, preset, smart_subsample,
+		near_lossless ) ) {
 		WebPPictureFree( &pic );
 		WebPMemoryWriterClear( &writer );
 		return -1;
@@ -189,7 +192,7 @@ 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 smart_subsample, gboolean near_lossless )
 {
 	WebPPicture pic;
 	WebPMemoryWriter writer;
@@ -205,7 +208,8 @@ vips__webp_write_buffer( VipsImage *in, void **obuf, size_t *olen,
 	pic.writer = WebPMemoryWrite;
 	pic.custom_ptr = &writer;
 
-	if( write_webp( &pic, in, Q, lossless, preset, smart_subsample ) ) {
+	if( write_webp( &pic, in, Q, lossless, preset, smart_subsample,
+		near_lossless) ) {
 		WebPPictureFree( &pic );
 		WebPMemoryWriterClear( &writer );
 		return -1;

libvips/foreign/webp.h

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

libvips/foreign/webpsave.c

@@ -68,6 +68,10 @@ typedef struct _VipsForeignSaveWebp {
 	 */
 	gboolean smart_subsample;
 
+	/* Use preprocessing in lossless mode.
+	 */
+	gboolean near_lossless;
+
 } VipsForeignSaveWebp;
 
 typedef VipsForeignSaveClass VipsForeignSaveWebpClass;
@@ -108,7 +112,7 @@ vips_foreign_save_webp_class_init( VipsForeignSaveWebpClass *class )
 		_( "Q factor" ),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
 		G_STRUCT_OFFSET( VipsForeignSaveWebp, Q ),
-		1, 100, 75 );
+		0, 100, 75 );
 
 	VIPS_ARG_BOOL( class, "lossless", 11, 
 		_( "lossless" ), 
@@ -132,6 +136,13 @@ vips_foreign_save_webp_class_init( VipsForeignSaveWebpClass *class )
 		G_STRUCT_OFFSET( VipsForeignSaveWebp, smart_subsample ),
 		FALSE );
 
+	VIPS_ARG_BOOL( class, "near_lossless", 14,
+		_( "Near lossless" ),
+		_( "Enable preprocessing in lossless mode (uses Q)" ),
+		VIPS_ARGUMENT_OPTIONAL_INPUT,
+		G_STRUCT_OFFSET( VipsForeignSaveWebp, near_lossless ),
+		FALSE );
+
 }
 
 static void
@@ -167,7 +178,7 @@ 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->smart_subsample, webp->near_lossless ) )
 		return( -1 );
 
 	return( 0 );
@@ -230,7 +241,7 @@ 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->smart_subsample, webp->near_lossless ) )
 		return( -1 );
 
 	blob = vips_blob_new( (VipsCallbackFn) vips_free, obuf, olen );
@@ -292,7 +303,7 @@ 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->smart_subsample, webp->near_lossless ) )
 		return( -1 );
 
 	printf( "Content-length: %zu\r\n", olen );