Index: source/blender/blenkernel/intern/mask_rasterize.c
===================================================================
--- source/blender/blenkernel/intern/mask_rasterize.c	(revision 49270)
+++ source/blender/blenkernel/intern/mask_rasterize.c	(working copy)
@@ -1272,6 +1272,8 @@
 			case MASK_BLEND_DIFFERENCE:
 				value = fabsf(value - value_layer);
 				break;
+			case MASK_BLEND_MERGE:
+				value += value_layer * (1.0f - value);
 			default: /* same as add */
 				BLI_assert(0);
 				value += value_layer;
Index: source/blender/blenkernel/intern/mask.c
===================================================================
--- source/blender/blenkernel/intern/mask.c	(revision 49270)
+++ source/blender/blenkernel/intern/mask.c	(working copy)
@@ -2613,6 +2613,16 @@
 				}
 				break;
 			}
+			case MASK_BLEND_MERGE:
+			{
+				if (alpha == 1.0f) {
+					merge_vn_vn(buffer, buffer_tmp, buffer_size);
+				}
+				else {
+					mmerge_vn_vn(buffer, buffer_tmp, alpha, buffer_size);
+				}
+				break;
+			}
 			case MASK_BLEND_ADD:
 			default:
 			{
Index: source/blender/makesdna/DNA_mask_types.h
===================================================================
--- source/blender/makesdna/DNA_mask_types.h	(revision 49270)
+++ source/blender/makesdna/DNA_mask_types.h	(working copy)
@@ -173,7 +173,8 @@
 	MASK_BLEND_DARKEN      = 3,
 	MASK_BLEND_MUL         = 4,
 	MASK_BLEND_REPLACE     = 5,
-	MASK_BLEND_DIFFERENCE  = 6
+	MASK_BLEND_DIFFERENCE  = 6,
+	MASK_BLEND_MERGE	   = 7
 };
 
 /* masklay->blend_flag */
Index: source/blender/makesrna/intern/rna_mask.c
===================================================================
--- source/blender/makesrna/intern/rna_mask.c	(revision 49270)
+++ source/blender/makesrna/intern/rna_mask.c	(working copy)
@@ -580,6 +580,7 @@
 		{MASK_BLEND_MUL, "MUL", 0, "Multiply", ""},
 		{MASK_BLEND_REPLACE, "REPLACE", 0, "Replace", ""},
 		{MASK_BLEND_DIFFERENCE, "DIFFERENCE", 0, "Difference", ""},
+		{MASK_BLEND_MERGE, "MERGE", 0, "Merge", ""},
 		{0, NULL, 0, NULL, NULL}
 	};
 
Index: source/blender/blenlib/BLI_math_vector.h
===================================================================
--- source/blender/blenlib/BLI_math_vector.h	(revision 49270)
+++ source/blender/blenlib/BLI_math_vector.h	(working copy)
@@ -235,6 +235,8 @@
 void add_vn_vnvn(float *array_tar, const float *array_src_a, const float *array_src_b, const int size);
 void madd_vn_vn(float *array_tar, const float *array_src, const float f, const int size);
 void madd_vn_vnvn(float *array_tar, const float *array_src_a, const float *array_src_b, const float f, const int size);
+void merge_vn_vn(float *array_tar, const float *array_src, const int size);
+void mmerge_vn_vn(float *array_tar, const float *array_src, const float f, const int size);
 void sub_vn_vn(float *array_tar, const float *array_src, const int size);
 void sub_vn_vnvn(float *array_tar, const float *array_src_a, const float *array_src_b, const int size);
 void msub_vn_vn(float *array_tar, const float *array_src, const float f, const int size);
Index: source/blender/blenlib/intern/math_vector.c
===================================================================
--- source/blender/blenlib/intern/math_vector.c	(revision 49270)
+++ source/blender/blenlib/intern/math_vector.c	(working copy)
@@ -584,6 +584,26 @@
 	}
 }
 
+void merge_vn_vn(float *array_tar, const float *array_src, const int size)
+{
+	float *tar = array_tar + (size - 1);
+	const float *src = array_src + (size - 1);
+	int i = size;
+	while (i--) {
+		*(tar--) += *(src--) * (1.0f - *(tar--));
+	}
+}
+
+void mmerge_vn_vn(float *array_tar, const float *array_src, const float f, const int size)
+{
+	float *tar = array_tar + (size - 1);
+	const float *src = array_src + (size - 1);
+	int i = size;
+	while (i--) {
+		*(tar--) += *(src--) * (1.0f - *(tar--)) * f;
+	}
+}
+
 void sub_vn_vn(float *array_tar, const float *array_src, const int size)
 {
 	float *tar = array_tar + (size - 1);