add 1/2/4 bit PNG save

- new @bitdepth param
- deprecate @colours param

ChangeLog

@@ -31,8 +31,9 @@
 - deprecate heifload autorotate -- it's now always on
 - revised resize improves accuracy [kleisauke]
 - add --vips-config flag to show configuration info
-- add "bitdepth" param to tiff load and save, deprecate "squash" [MathemanFlo]
+- add "bitdepth" param to tiff save, deprecate "squash" [MathemanFlo]
 - tiff load and save now supports 2 and 4 bit data [MathemanFlo]
+- pngsave @bitdepth parameter lets you write 1, 2 and 4 bit PNGs
 - ppmsave also uses "bitdepth" now, for consistency
 
 24/4/20 started 8.9.3

libvips/foreign/pforeign.h

@@ -184,7 +184,8 @@ extern const char *vips__png_suffs[];
 int vips__png_write_target( VipsImage *in, VipsTarget *target,
 	int compress, int interlace, const char *profile,
 	VipsForeignPngFilter filter, gboolean strip,
-	gboolean palette, int colours, int Q, double dither );
+	gboolean palette, int Q, double dither,
+	int bitdepth );
 
 /* Map WEBP metadata names to vips names.
  */

libvips/foreign/pngsave.c

@@ -6,6 +6,8 @@
  * 	- compression should be 0-9, not 1-10
  * 20/6/18 [felixbuenemann]
  * 	- support png8 palette write with palette, colours, Q, dither
+ * 24/6/20
+ * 	- add @bitdepth, deprecate @colours
  */
 
 /*
@@ -63,9 +65,17 @@ typedef struct _VipsForeignSavePng {
 	char *profile;
 	VipsForeignPngFilter filter;
 	gboolean palette;
-	int colours;
 	int Q;
 	double dither;
+	int bitdepth;
+
+	/* Set by subclasses.
+	 */
+	VipsTarget *target;
+
+	/* Deprecated.
+	 */
+	int colours;
 } VipsForeignSavePng;
 
 typedef VipsForeignSaveClass VipsForeignSavePngClass;
@@ -73,6 +83,55 @@ typedef VipsForeignSaveClass VipsForeignSavePngClass;
 G_DEFINE_ABSTRACT_TYPE( VipsForeignSavePng, vips_foreign_save_png, 
 	VIPS_TYPE_FOREIGN_SAVE );
 
+static void
+vips_foreign_save_png_dispose( GObject *gobject )
+{
+	VipsForeignSavePng *png = (VipsForeignSavePng *) gobject;
+
+	if( png->target ) 
+		vips_target_finish( png->target );
+	VIPS_UNREF( png->target );
+
+	G_OBJECT_CLASS( vips_foreign_save_png_parent_class )->
+		dispose( gobject );
+}
+
+static int
+vips_foreign_save_png_build( VipsObject *object )
+{
+	VipsForeignSave *save = (VipsForeignSave *) object;
+	VipsForeignSavePng *png = (VipsForeignSavePng *) object;
+
+	if( VIPS_OBJECT_CLASS( vips_foreign_save_png_parent_class )->
+		build( object ) )
+		return( -1 );
+
+	/* Deprecated "colours" arg just sets bitdepth large enough to hold
+	 * that many colours.
+	 */
+        if( vips_object_argument_isset( object, "colours" ) ) 
+		png->bitdepth = ceil( log2( png->colours ) );
+
+        if( !vips_object_argument_isset( object, "bitdepth" ) ) 
+		png->bitdepth = 
+			save->ready->BandFmt == VIPS_FORMAT_UCHAR ? 8 : 16;
+
+	/* If this is a RGB or RGBA image and a low bit depth has been
+	 * requested, enable palettization.
+	 */
+        if( save->ready->Bands > 2 &&
+		png->bitdepth < 8 )
+		png->palette = TRUE;
+
+	if( vips__png_write_target( save->ready, png->target,
+		png->compression, png->interlace, png->profile, png->filter,
+		save->strip, png->palette, png->Q, png->dither,
+		png->bitdepth ) )
+		return( -1 );
+
+	return( 0 );
+}
+
 /* Save a bit of typing.
  */
 #define UC VIPS_FORMAT_UCHAR
@@ -99,11 +158,13 @@ vips_foreign_save_png_class_init( VipsForeignSavePngClass *class )
 	VipsForeignClass *foreign_class = (VipsForeignClass *) class;
 	VipsForeignSaveClass *save_class = (VipsForeignSaveClass *) class;
 
+	gobject_class->dispose = vips_foreign_save_png_dispose;
 	gobject_class->set_property = vips_object_set_property;
 	gobject_class->get_property = vips_object_get_property;
 
 	object_class->nickname = "pngsave_base";
 	object_class->description = _( "save png" );
+	object_class->build = vips_foreign_save_png_build;
 
 	foreign_class->suffs = vips__png_suffs;
 
@@ -146,13 +207,6 @@ vips_foreign_save_png_class_init( VipsForeignSavePngClass *class )
 		G_STRUCT_OFFSET( VipsForeignSavePng, palette ),
 		FALSE );
 
-	VIPS_ARG_INT( class, "colours", 14,
-		_( "Colours" ),
-		_( "Max number of palette colours" ),
-		VIPS_ARGUMENT_OPTIONAL_INPUT,
-		G_STRUCT_OFFSET( VipsForeignSavePng, colours ),
-		2, 256, 256 );
-
 	VIPS_ARG_INT( class, "Q", 15,
 		_( "Quality" ),
 		_( "Quantisation quality" ),
@@ -167,6 +221,20 @@ vips_foreign_save_png_class_init( VipsForeignSavePngClass *class )
 		G_STRUCT_OFFSET( VipsForeignSavePng, dither ),
 		0.0, 1.0, 1.0 );
 
+	VIPS_ARG_INT( class, "bitdepth", 17,
+		_( "Bit depth" ),
+		_( "Write as a 1, 2, 4 or 8 bit image" ),
+		VIPS_ARGUMENT_OPTIONAL_INPUT,
+		G_STRUCT_OFFSET( VipsForeignSavePng, bitdepth ),
+		0, 8, 0 );
+
+	VIPS_ARG_INT( class, "colours", 14,
+		_( "Colours" ),
+		_( "Max number of palette colours" ),
+		VIPS_ARGUMENT_OPTIONAL_INPUT | VIPS_ARGUMENT_DEPRECATED,
+		G_STRUCT_OFFSET( VipsForeignSavePng, colours ),
+		2, 256, 256 );
+
 }
 
 static void
@@ -174,7 +242,6 @@ vips_foreign_save_png_init( VipsForeignSavePng *png )
 {
 	png->compression = 6;
 	png->filter = VIPS_FOREIGN_PNG_FILTER_ALL;
-	png->colours = 256;
 	png->Q = 100;
 	png->dither = 1.0;
 }
@@ -193,19 +260,16 @@ G_DEFINE_TYPE( VipsForeignSavePngTarget, vips_foreign_save_png_target,
 static int
 vips_foreign_save_png_target_build( VipsObject *object )
 {
-	VipsForeignSave *save = (VipsForeignSave *) object;
 	VipsForeignSavePng *png = (VipsForeignSavePng *) object;
 	VipsForeignSavePngTarget *target = (VipsForeignSavePngTarget *) object;
 
+	png->target = target->target;
+	g_object_ref( png->target );
+
 	if( VIPS_OBJECT_CLASS( vips_foreign_save_png_target_parent_class )->
 		build( object ) )
 		return( -1 );
 
-	if( vips__png_write_target( save->ready, target->target,
-		png->compression, png->interlace, png->profile, png->filter,
-		save->strip, png->palette, png->colours, png->Q, png->dither ) )
-		return( -1 );
-
 	return( 0 );
 }
 
@@ -250,27 +314,16 @@ G_DEFINE_TYPE( VipsForeignSavePngFile, vips_foreign_save_png_file,
 static int
 vips_foreign_save_png_file_build( VipsObject *object )
 {
-	VipsForeignSave *save = (VipsForeignSave *) object;
 	VipsForeignSavePng *png = (VipsForeignSavePng *) object;
-	VipsForeignSavePngFile *png_file = (VipsForeignSavePngFile *) object;
+	VipsForeignSavePngFile *file = (VipsForeignSavePngFile *) object;
 
-	VipsTarget *target;
+	if( !(png->target = vips_target_new_to_file( file->filename )) )
+		return( -1 );
 
 	if( VIPS_OBJECT_CLASS( vips_foreign_save_png_file_parent_class )->
 		build( object ) )
 		return( -1 );
 
-	if( !(target = vips_target_new_to_file( png_file->filename )) )
-		return( -1 );
-	if( vips__png_write_target( save->ready, target, 
-		png->compression, png->interlace, 
-		png->profile, png->filter, save->strip, png->palette,
-		png->colours, png->Q, png->dither ) ) {
-		VIPS_UNREF( target );
-		return( -1 );
-	}
-	VIPS_UNREF( target );
-
 	return( 0 );
 }
 
@@ -314,34 +367,22 @@ G_DEFINE_TYPE( VipsForeignSavePngBuffer, vips_foreign_save_png_buffer,
 static int
 vips_foreign_save_png_buffer_build( VipsObject *object )
 {
-	VipsForeignSave *save = (VipsForeignSave *) object;
 	VipsForeignSavePng *png = (VipsForeignSavePng *) object;
 	VipsForeignSavePngBuffer *buffer = (VipsForeignSavePngBuffer *) object;
 
-	VipsTarget *target;
 	VipsBlob *blob;
 
+	if( !(png->target = vips_target_new_to_memory()) )
+		return( -1 );
+
 	if( VIPS_OBJECT_CLASS( vips_foreign_save_png_buffer_parent_class )->
 		build( object ) )
 		return( -1 );
 
-	if( !(target = vips_target_new_to_memory()) )
+	g_object_get( png->target, "blob", &blob, NULL );
-		return( -1 );
-
-	if( vips__png_write_target( save->ready, target,
-		png->compression, png->interlace, png->profile, png->filter,
-		save->strip, png->palette, png->colours, png->Q, 
-		png->dither ) ) {
-		VIPS_UNREF( target );
-		return( -1 );
-	}
-
-	g_object_get( target, "blob", &blob, NULL );
 	g_object_set( buffer, "buffer", blob, NULL );
 	vips_area_unref( VIPS_AREA( blob ) );
 
-	VIPS_UNREF( target );
-
 	return( 0 );
 }
 
@@ -386,9 +427,9 @@ vips_foreign_save_png_buffer_init( VipsForeignSavePngBuffer *buffer )
  * * @profile: %gchararray, ICC profile to embed
  * * @filter: #VipsForeignPngFilter row filter flag(s)
  * * @palette: %gboolean, enable quantisation to 8bpp palette
- * * @colours: %gint, max number of palette colours for quantisation
+ * * @Q: %gint, quality for 8bpp quantisation 
- * * @Q: %gint, quality for 8bpp quantisation (does not exceed @colours)
  * * @dither: %gdouble, amount of dithering for 8bpp quantization
+ * * @bitdepth: %int, set write bit depth to 1, 2, 4 or 8
  *
  * Write a VIPS image to a file as PNG.
  *
@@ -414,13 +455,15 @@ vips_foreign_save_png_buffer_init( VipsForeignSavePngBuffer *buffer )
  * alpha before saving. Images with more than one byte per band element are
  * saved as 16-bit PNG, others are saved as 8-bit PNG.
  *
- * Set @palette to %TRUE to enable quantisation to an 8-bit per pixel palette
+ * Set @palette to %TRUE to enable palette mode for RGB or RGBA images. A
- * image with alpha transparency support. If @colours is given, it limits the
+ * palette will be computed with enough space for @bitdepth (1, 2, 4 or 8) 
- * maximum number of palette entries. Similar to JPEG the quality can also be
+ * bits. Use @Q to set the optimisation effort, and @dither to set the degree of
- * be changed with the @Q parameter which further reduces the palette size and
+ * Floyd-Steinberg dithering.
- * @dither controls the amount of Floyd-Steinberg dithering.
  * This feature requires libvips to be compiled with libimagequant.
  *
+ * You can also set @bitdepth for mono and mono + alpha images, and the image
+ * will be quantized.
+ *
  * XMP metadata is written to the XMP chunk. PNG comments are written to
  * separate text chunks.
  *
@@ -455,9 +498,9 @@ vips_pngsave( VipsImage *in, const char *filename, ... )
  * * @profile: %gchararray, ICC profile to embed
  * * @filter: #VipsForeignPngFilter row filter flag(s)
  * * @palette: %gboolean, enable quantisation to 8bpp palette
- * * @colours: %gint, max number of palette colours for quantisation
+ * * @Q: %gint, quality for 8bpp quantisation 
- * * @Q: %gint, quality for 8bpp quantisation (does not exceed @colours)
  * * @dither: %gdouble, amount of dithering for 8bpp quantization
+ * * @bitdepth: %int, set write bit depth to 1, 2, 4 or 8
  *
  * As vips_pngsave(), but save to a memory buffer. 
  *
@@ -510,9 +553,9 @@ vips_pngsave_buffer( VipsImage *in, void **buf, size_t *len, ... )
  * * @profile: ICC profile to embed
  * * @filter: libpng row filter flag(s)
  * * @palette: enable quantisation to 8bpp palette
- * * @colours: max number of palette colours for quantisation
+ * * @Q: quality for 8bpp quantisation 
- * * @Q: quality for 8bpp quantisation (does not exceed @colours)
  * * @dither: amount of dithering for 8bpp quantization
+ * * @bitdepth: %int, set write bit depth to 1, 2, 4 or 8
  *
  * As vips_pngsave(), but save to a target.
  *

libvips/foreign/vipspng.c

@@ -355,7 +355,7 @@ static int
 png2vips_header( Read *read, VipsImage *out )
 {
 	png_uint_32 width, height;
-	int bit_depth, color_type;
+	int bitdepth, color_type;
 	int interlace_type;
 
 	png_uint_32 res_x, res_y;
@@ -385,7 +385,7 @@ png2vips_header( Read *read, VipsImage *out )
 		return( -1 );
 
 	png_get_IHDR( read->pPng, read->pInfo, 
-		&width, &height, &bit_depth, &color_type,
+		&width, &height, &bitdepth, &color_type,
 		&interlace_type, NULL, NULL );
 
 	/* png_get_channels() gives us 1 band for palette images ... so look
@@ -413,7 +413,7 @@ png2vips_header( Read *read, VipsImage *out )
 		return( -1 );
 	}
 
-	if( bit_depth > 8 ) {
+	if( bitdepth > 8 ) {
 		if( bands < 3 )
 			interpretation = VIPS_INTERPRETATION_GREY16;
 		else
@@ -448,13 +448,13 @@ png2vips_header( Read *read, VipsImage *out )
 	/* Expand <8 bit images to full bytes.
 	 */
 	if( color_type == PNG_COLOR_TYPE_GRAY &&
-		bit_depth < 8 ) 
+		bitdepth < 8 ) 
 		png_set_expand_gray_1_2_4_to_8( read->pPng );
 
 	/* If we're an INTEL byte order machine and this is 16bits, we need
 	 * to swap bytes.
 	 */
-	if( bit_depth > 8 && 
+	if( bitdepth > 8 && 
 		!vips_amiMSBfirst() )
 		png_set_swap( read->pPng );
 
@@ -480,8 +480,7 @@ png2vips_header( Read *read, VipsImage *out )
 	 */
 	vips_image_init_fields( out,
 		width, height, bands,
-		bit_depth > 8 ? 
+		bitdepth > 8 ? VIPS_FORMAT_USHORT : VIPS_FORMAT_UCHAR,
-			VIPS_FORMAT_USHORT : VIPS_FORMAT_UCHAR,
 		VIPS_CODING_NONE, interpretation, 
 		Xres, Yres );
 
@@ -556,7 +555,7 @@ png2vips_header( Read *read, VipsImage *out )
 	/* Attach original palette bit depth, if any, as metadata.
 	 */
 	if( color_type == PNG_COLOR_TYPE_PALETTE )
-		vips_image_set_int( out, "palette-bit-depth", bit_depth );
+		vips_image_set_int( out, "palette-bit-depth", bitdepth );
 
 	return( 0 );
 }
@@ -924,11 +923,11 @@ static int
 write_vips( Write *write, 
 	int compress, int interlace, const char *profile,
 	VipsForeignPngFilter filter, gboolean strip,
-	gboolean palette, int colours, int Q, double dither )
+	gboolean palette, int Q, double dither,
+	int bitdepth )
 {
 	VipsImage *in = write->in;
 
-	int bit_depth;
 	int color_type;
 	int interlace_type;
 	int i, nb_passes;
@@ -970,8 +969,6 @@ write_vips( Write *write,
 	 */
 	png_set_filter( write->pPng, 0, filter );
 
-	bit_depth = in->BandFmt == VIPS_FORMAT_UCHAR ? 8 : 16;
-
 	switch( in->Bands ) {
 	case 1: color_type = PNG_COLOR_TYPE_GRAY; break;
 	case 2: color_type = PNG_COLOR_TYPE_GRAY_ALPHA; break;
@@ -987,12 +984,8 @@ write_vips( Write *write,
 #ifdef HAVE_IMAGEQUANT
 	/* Enable image quantisation to paletted 8bpp PNG if colours is set.
 	 */
-	if( palette ) {
+	if( palette ) 
-		g_assert( colours >= 2 && 
-			colours <= 256 );
-		bit_depth = 8;
 		color_type = PNG_COLOR_TYPE_PALETTE;
-	}
 #else
 	if( palette )
 		g_warning( "%s",
@@ -1002,7 +995,7 @@ write_vips( Write *write,
 	interlace_type = interlace ? PNG_INTERLACE_ADAM7 : PNG_INTERLACE_NONE;
 
 	png_set_IHDR( write->pPng, write->pInfo, 
-		in->Xsize, in->Ysize, bit_depth, color_type, interlace_type, 
+		in->Xsize, in->Ysize, bitdepth, color_type, interlace_type, 
 		PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT );
 
 	/* Set resolution. libpng uses pixels per meter.
@@ -1107,7 +1100,7 @@ write_vips( Write *write,
 		int trans_count;
 
 		if( vips__quantise_image( in, &im_index, &im_palette, 
-			colours, Q, dither ) ) 
+			1 << bitdepth, Q, dither ) ) 
 			return( -1 );
 
 		palette_count = im_palette->Xsize;
@@ -1167,10 +1160,14 @@ write_vips( Write *write,
 	/* If we're an intel byte order CPU and this is a 16bit image, we need
 	 * to swap bytes.
 	 */
-	if( bit_depth > 8 && 
+	if( bitdepth > 8 && 
 		!vips_amiMSBfirst() ) 
 		png_set_swap( write->pPng ); 
 
+	/* If bitdepth is 1/2/4, pack pixels into bytes.
+	 */
+	png_set_packing( write->pPng );
+
 	if( interlace )	
 		nb_passes = png_set_interlace_handling( write->pPng );
 	else
@@ -1196,7 +1193,8 @@ int
 vips__png_write_target( VipsImage *in, VipsTarget *target,
 	int compression, int interlace,
 	const char *profile, VipsForeignPngFilter filter, gboolean strip,
-	gboolean palette, int colours, int Q, double dither )
+	gboolean palette, int Q, double dither,
+	int bitdepth )
 {
 	Write *write;
 
@@ -1205,7 +1203,7 @@ vips__png_write_target( VipsImage *in, VipsTarget *target,
 
 	if( write_vips( write, 
 		compression, interlace, profile, filter, strip, palette,
-		colours, Q, dither ) ) {
+		Q, dither, bitdepth ) ) {
 		write_finish( write );
 		vips_error( "vips2png", 
 			"%s", _( "unable to write to target" ) );

test/test-suite/test_foreign.py

@@ -313,6 +313,22 @@ class TestForeign:
         self.save_load_file(".png", "[interlace]", self.colour, 0)
         self.save_load_file(".png", "[interlace]", self.mono, 0)
 
+        # size of a regular mono PNG 
+        len_mono = len(self.mono.write_to_buffer(".png"))
+
+        # 4-bit should be smaller
+        len_mono4 = len(self.mono.write_to_buffer(".png", bitdepth=4))
+        assert( len_mono4 < len_mono )
+
+        len_mono2 = len(self.mono.write_to_buffer(".png", bitdepth=2))
+        assert( len_mono2 < len_mono4 )
+
+        len_mono1 = len(self.mono.write_to_buffer(".png", bitdepth=1))
+        assert( len_mono1 < len_mono2 )
+
+        # we can't test palette save since we can't be sure libimagequant is
+        # available
+
     @skip_if_no("tiffload")
     def test_tiff(self):
         def tiff_valid(im):