add exif support to png load/save (#3168)

* start adding exif in png

the "Exif\0\0" header isn't being added and removed correctly

needs tests

* all done

tested with linpng and libspng

ChangeLog

@@ -23,6 +23,7 @@ master
 - fits write doesn't duplicate header fields
 - add @wrap to vips_text()
 - GIF load supports truncated frames [tlsa]
+- EXIF support for PNG load and save
 
 9/11/22 started 8.13.4
 - missing include in mosaic_fuzzer [ServOKio]

libvips/foreign/spngsave.c

@@ -12,6 +12,8 @@
  * 	- use libspng for save
  * 15/7/22 [lovell]
  * 	- default filter to none
+ * 17/11/22
+ * 	- add exif save
  */
 
 /*
@@ -56,6 +58,7 @@
 #include <string.h>
 
 #include <vips/vips.h>
+#include <vips/internal.h>
 
 #include "pforeign.h"
 #include "quantise.h"
@@ -244,6 +247,25 @@ vips_foreign_save_spng_metadata( VipsForeignSaveSpng *spng, VipsImage *in )
 		g_free( str );
 	}
 
+	if( vips_image_get_typeof( in, VIPS_META_EXIF_NAME ) ) {
+		struct spng_exif exif;
+
+		if( vips__exif_update( in ) ||
+			vips_image_get_blob( in, VIPS_META_EXIF_NAME, 
+				(const void **) &exif.data, &exif.length ) )
+			return( -1 );
+
+		/* libspng does not want the JFIF "Exif\0\0" prefix.
+		 */
+		if( exif.length >= 6 &&
+			vips_isprefix( "Exif", exif.data ) ) {
+			exif.data += 6;
+			exif.length -= 6;
+		}
+
+		spng_set_exif( spng->ctx, &exif );
+	}
+
 	if( vips_image_map( in, vips_foreign_save_spng_comment, spng ) )
 		return( -1 );
 

libvips/foreign/vipspng.c

@@ -85,6 +85,8 @@
  *	-  add "unlimited" flag to png load
  * 13/1/22
  * 	- raise libpng pixel size limit to VIPS_MAX_COORD 
+ * 17/11/22
+ * 	- add exif read/write
  */
 
 /*
@@ -638,6 +640,17 @@ png2vips_header( Read *read, VipsImage *out )
 }
 #endif /*PNG_bKGD_SUPPORTED*/
 
+#ifdef PNG_eXIf_SUPPORTED
+{
+	png_uint_32 num_exif;
+	png_bytep exif;
+
+	if( png_get_eXIf_1( read->pPng, read->pInfo, &num_exif, &exif ) )
+		vips_image_set_blob_copy( out, VIPS_META_EXIF_NAME, 
+			exif, num_exif );
+}
+#endif /*PNG_eXIf_SUPPORTED*/
+
 	return( 0 );
 }
 
@@ -1173,8 +1186,30 @@ write_vips( Write *write,
 			g_free( str );
 		}
 
-		if( vips_image_map( in,
+#ifdef PNG_eXIf_SUPPORTED
-			write_png_comment, write ) )
+		if( vips_image_get_typeof( in, VIPS_META_EXIF_NAME ) ) {
+			const void *data;
+			size_t length;
+
+			if( vips__exif_update( in ) ||
+				vips_image_get_blob( in, VIPS_META_EXIF_NAME, 
+					&data, &length ) )
+				return( -1 );
+
+			/* libpng does not want the JFIF "Exif\0\0" prefix.
+			 */
+			if( length >= 6 &&
+				vips_isprefix( "Exif", (char *) data ) ) {
+				data += 6;
+				length -= 6;
+			}
+
+			png_set_eXIf_1( write->pPng, write->pInfo,
+				length, (png_bytep) data );
+		}
+#endif /*PNG_eXIf_SUPPORTED*/
+
+		if( vips_image_map( in, write_png_comment, write ) )
 			return( -1 );
 	}
 

test/test-suite/test_foreign.py

@@ -457,6 +457,25 @@ class TestForeign:
         # we can't test palette save since we can't be sure libimagequant is
         # available and there's no easy test for its presence
 
+        # see if we have exif parsing: our test jpg image has this field
+        x = pyvips.Image.new_from_file(JPEG_FILE)
+        if x.get_typeof("exif-ifd0-Orientation") != 0:
+            # we need a copy of the image to set the new metadata on
+            # otherwise we get caching problems
+
+            # can set, save and load new orientation
+            x = pyvips.Image.new_from_file(JPEG_FILE)
+            x = x.copy()
+
+            x.set("orientation", 2)
+
+            filename = temp_filename(self.tempdir, '.png')
+            x.write_to_file(filename)
+
+            x = pyvips.Image.new_from_file(filename)
+            y = x.get("orientation")
+            assert y == 2
+
     @skip_if_no("tiffload")
     def test_tiff(self):
         def tiff_valid(im):