From ab5476f270777f19ccec7250fabce4e9ca4dc9fc Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Mon, 20 Apr 2009 16:02:28 +0000
Subject: [PATCH] stuff

---
 ChangeLog                      | 1 +
 libsrc/format/im_magick2vips.c | 7 +++++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 58aefe96..f838cd02 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -5,6 +5,7 @@
 - fix includes for gtk+-3.0
 - report virtual memory too in im__print_all()
 - cosmetic changes to nohalo
+- im_magick2vips() needs to invert alpha
 
 25/3/09 started 7.18.0
 - revised version numbers
diff --git a/libsrc/format/im_magick2vips.c b/libsrc/format/im_magick2vips.c
index b187677a..7002df07 100644
--- a/libsrc/format/im_magick2vips.c
+++ b/libsrc/format/im_magick2vips.c
@@ -24,6 +24,9 @@
  * 	- allow funky bit depths, like 14 (thanks Mikkel)
  * 17/3/09
  * 	- reset dcm:display-range to help DICOM read
+ * 20/4/09
+ * 	- argh libMagick uses 255 == transparent ... we must invert all 
+ * 	  alpha channels
  */
 
 /*
@@ -401,7 +404,7 @@ parse_header( Read *read )
 	\
 	for( x = 0; x < n; x++ ) { \
 		q[0] = pixels[x].green / SCALE( MAX ); \
-		q[1] = pixels[x].opacity / SCALE( MAX ); \
+		q[1] = MAX - pixels[x].opacity / SCALE( MAX ); \
 		\
 		q += 2; \
 	} \
@@ -426,7 +429,7 @@ parse_header( Read *read )
 		q[0] = pixels[x].red / SCALE( MAX ); \
 		q[1] = pixels[x].green / SCALE( MAX ); \
 		q[2] = pixels[x].blue / SCALE( MAX ); \
-		q[3] = pixels[x].opacity / SCALE( MAX ); \
+		q[3] = MAX - pixels[x].opacity / SCALE( MAX ); \
 		\
 		q += 4; \
 	} \