[Bf-blender-cvs] SVN commit: /data/svn/bf-blender [59401] trunk/blender/source/blender/imbuf /intern/imageprocess.c: Fix #36535: Color difference when saving image

[Sergey Sharybin]

Revision: 59401
          http://projects.blender.org/scm/viewvc.php?view=rev&root=bf-blender&revision=59401
Author:   nazgul
Date:     2013-08-23 08:27:01 +0000 (Fri, 23 Aug 2013)
Log Message:
-----------
Fix #36535: Color difference when saving image

Issue was caused by precision loss in alpha under code.
Now it might be slower a bit, but it's as precise as it
could be. At least i hope so :)

Modified Paths:
--------------
    trunk/blender/source/blender/imbuf/intern/imageprocess.c

Modified: trunk/blender/source/blender/imbuf/intern/imageprocess.c
===================================================================
--- trunk/blender/source/blender/imbuf/intern/imageprocess.c	2013-08-23 07:14:22 UTC (rev 59400)
+++ trunk/blender/source/blender/imbuf/intern/imageprocess.c	2013-08-23 08:27:01 UTC (rev 59401)
@@ -359,17 +359,21 @@
 	unsigned char *cp = rect;
 
 	while (a--) {
-		if (cp[3] == 0) {
+		if (cp[3] == 255) {
+			/* pass */
+		}
+		else if (cp[3] == 0) {
 			cp[0] = backcol[0] * 255;
 			cp[1] = backcol[1] * 255;
 			cp[2] = backcol[2] * 255;
 		}
 		else {
-			int mul = 255 - cp[3];
+			float alpha = cp[3] / 255.0;
+			float mul = 1.0f - alpha;
 
-			cp[0] = (cp[0] * cp[3] >> 8) + mul * backcol[0] / 255;
-			cp[1] = (cp[1] * cp[3] >> 8) + mul * backcol[1] / 255;
-			cp[2] = (cp[2] * cp[3] >> 8) + mul * backcol[2] / 255;
+			cp[0] = (cp[0] * alpha) + mul * backcol[0];
+			cp[1] = (cp[1] * alpha) + mul * backcol[1];
+			cp[2] = (cp[2] * alpha) + mul * backcol[2];
 		}
 
 		cp[3] = 255;