fix write RGBA as JPG

it was saving RGBA as CMYK JPG, with comical results (thanks Tobias)

ChangeLog

@@ -6,6 +6,7 @@
 - add dzsave, save in deep zoom format
 - rework im_shrink() as a class
 - remove im_rightshift_size(), just a convenience function now
+- fix write RGBA as JPG (thanks Tobias)
 
 19/4/12 started 7.28.6
 - better resolution unit handling in deprecated im_vips2tiff()

TODO

@@ -2,10 +2,6 @@
 
 - add a int-only path?
 
-- compare to rightshift_size, deprecate that? should be as quick
-
-- warn if used with float factors
-
 - vipsthumbnail should not remove profiles by default
 
 

libvips/foreign/foreign.c

@@ -1160,9 +1160,18 @@ vips_foreign_convert_saveable( VipsForeignSave *save )
 			in = out;
 		}
 		else if( in->Bands > 3 && 
-			class->saveable == VIPS_SAVEABLE_RGB ) {
+			(class->saveable == VIPS_SAVEABLE_RGB ||
+			 (class->saveable == VIPS_SAVEABLE_RGB_CMYK &&
+			  in->Type != VIPS_INTERPRETATION_CMYK)) ) { 
 			VipsImage *out;
 
+			/* Don't let 4 bands though unless the image really is
+			 * a CMYK.
+			 *
+			 * Consider a RGBA png being saved as JPG. We can
+			 * write CMYK jpg, but we mustn't do that for RGBA
+			 * images.
+			 */
 			if( vips_extract_band( in, &out, 0, 
 				"n", 3,
 				NULL ) ) {
@@ -1174,7 +1183,8 @@ vips_foreign_convert_saveable( VipsForeignSave *save )
 			in = out;
 		}
 		else if( in->Bands > 4 && 
-			(class->saveable == VIPS_SAVEABLE_RGB_CMYK || 
+			((class->saveable == VIPS_SAVEABLE_RGB_CMYK &&
+			  in->Type == VIPS_INTERPRETATION_CMYK) ||
 			 class->saveable == VIPS_SAVEABLE_RGBA) ) {
 			VipsImage *out;
 

libvips/foreign/vipspng.c

@@ -43,6 +43,9 @@
  * 15/3/12
  * 	- better alpha handling
  * 	- sanity check pixel geometry before allowing read
+ * 17/6/12
+ * 	- more alpha fixes ... some images have no transparency chunk but
+ * 	  still set color_type to alpha
  */
 
 /*
@@ -263,6 +266,13 @@ png2vips_header( Read *read, VipsImage *out )
 		png_set_tRNS_to_alpha( read->pPng );
 		bands += 1;
 	}
+	else if( color_type == PNG_COLOR_TYPE_GRAY_ALPHA || 
+		color_type == PNG_COLOR_TYPE_RGB_ALPHA ) {
+		/* Some images have no transparency chunk, but still set
+		 * color_type to alpha.
+		 */
+		bands += 1;
+	}
 
 	/* Expand <8 bit images to full bytes.
 	 */

libvips/resample/shrink.c

@@ -326,10 +326,11 @@ vips_shrink_build( VipsObject *object )
 	 * be OK, but FATSTRIP would be a disaster: thread 2 would be given a
 	 * strip some way down the output, which would be a huge distance down
 	 * the input.
+	 *
+	 * Make sure we always work by insisting on SMALLTILE.
 	 */
 	vips_demand_hint( resample->out, 
-		//VIPS_DEMAND_STYLE_SMALLTILE, resample->in, NULL );
-		VIPS_DEMAND_STYLE_THINSTRIP, resample->in, NULL );
+		VIPS_DEMAND_STYLE_SMALLTILE, resample->in, NULL );
 
 	/* Size output. Note: we round the output width down!
 	 */