[gimp] app: improve vivid-light formula

[Øyvind Kolås <ok src gnome org>]

commit 5978def585fdee633eb8581fa68c7436ddeaad73
Author: Øyvind Kolås <pippin gimp org>
Date:   Mon Jan 23 22:39:42 2017 +0100

    app: improve vivid-light formula

 app/operations/layer-modes/gimpblendcomposite.h |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/app/operations/layer-modes/gimpblendcomposite.h b/app/operations/layer-modes/gimpblendcomposite.h
index 6ee6292..1a0b555 100644
--- a/app/operations/layer-modes/gimpblendcomposite.h
+++ b/app/operations/layer-modes/gimpblendcomposite.h
@@ -1150,12 +1150,13 @@ blendfun_vivid_light (const float *dest,
 
               if (src[c] > 0.5f)
                 {
-                  comp = (1.0f - (1.0f - dest[c]) / (2.0f * (src[c] - 0.5f)));
+                  comp = (1.0f - (1.0f - dest[c]) / (2.0f * (src[c])));
                 }
               else
                 {
-                  comp = dest[c] / (1.0f - 2.0f * src[c]);
+                  comp = dest[c] / (1.0f - 2.0f * (src[c] - 0.5));
                 }
+              comp = MIN (comp, 1.0f);
 
               out[c] = comp;
             }