[gegl] operations: channel-mixer works on a perceptual color space

[Téo Mazars <teom src gnome org>]

commit f1f6a3dd2645b7ebf588ecef9d67fe608929731b
Author: Téo Mazars <teo mazars ensimag fr>
Date:   Tue Aug 6 21:18:36 2013 +0200

    operations: channel-mixer works on a perceptual color space
    
    It's a bit arbitrary here, but it keeps compatibility with GIMP and
    the behaviour feels slightly more coherent.

 operations/common/channel-mixer.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/operations/common/channel-mixer.c b/operations/common/channel-mixer.c
index a393dd7..ed478dc 100644
--- a/operations/common/channel-mixer.c
+++ b/operations/common/channel-mixer.c
@@ -149,12 +149,12 @@ static void prepare (GeglOperation *operation)
   if (input_format == NULL || babl_format_has_alpha (input_format))
     {
       mix->has_alpha = TRUE;
-      format = babl_format ("RGBA float");
+      format = babl_format ("R'G'B'A float");
     }
   else
     {
       mix->has_alpha = FALSE;
-      format = babl_format ("RGB float");
+      format = babl_format ("R'G'B' float");
     }
 
   gegl_operation_set_format (operation, "input", format);