Index: release/scripts/startup/bl_ui/properties_texture.py
===================================================================
--- release/scripts/startup/bl_ui/properties_texture.py	(revision 48705)
+++ release/scripts/startup/bl_ui/properties_texture.py	(working copy)
@@ -219,7 +219,10 @@
         col.label(text="Adjust:")
         col.prop(tex, "intensity")
         col.prop(tex, "contrast")
-        col.prop(tex, "saturation")
+        sub = col.row()
+        sub.active = not tex.use_negative_bricont
+        sub.prop(tex, "saturation")
+        col.prop(tex, "use_negative_bricont", text="Allow negative values")
 
 # Texture Slot Panels #
 
Index: source/blender/makesdna/DNA_texture_types.h
===================================================================
--- source/blender/makesdna/DNA_texture_types.h	(revision 48705)
+++ source/blender/makesdna/DNA_texture_types.h	(working copy)
@@ -373,6 +373,7 @@
 #define TEX_REPEAT_YMIR		256
 #define TEX_FLAG_MASK		( TEX_COLORBAND | TEX_FLIPBLEND | TEX_NEGALPHA | TEX_CHECKER_ODD | TEX_CHECKER_EVEN | TEX_PRV_ALPHA | TEX_PRV_NOR | TEX_REPEAT_XMIR | TEX_REPEAT_YMIR ) 
 #define TEX_DS_EXPAND		512
+#define TEX_NEGATIVE_BRICONT	1024
 
 /* extend (starts with 1 because of backward comp.) */
 #define TEX_EXTEND		1
Index: source/blender/makesrna/intern/rna_texture.c
===================================================================
--- source/blender/makesrna/intern/rna_texture.c	(revision 48705)
+++ source/blender/makesrna/intern/rna_texture.c	(working copy)
@@ -377,6 +377,14 @@
 		tex->coba = add_colorband(0);
 }
 
+static void rna_Texture_use_negative_bricont_set(PointerRNA *ptr, int value)
+{
+	Tex *tex= (Tex*)ptr->data;
+
+	if(value) tex->flag |= TEX_NEGATIVE_BRICONT;
+	else tex->flag &= ~TEX_NEGATIVE_BRICONT;
+}
+
 static void rna_Texture_use_nodes_set(PointerRNA *ptr, int v)
 {
 	Tex *tex = (Tex *)ptr->data;
@@ -1983,6 +1991,12 @@
 	RNA_def_property_range(prop, 0, 2);
 	RNA_def_property_ui_text(prop, "Saturation", "Adjust the saturation of colors in the texture");
 	RNA_def_property_update(prop, 0, "rna_Texture_update");
+
+	prop= RNA_def_property(srna, "use_negative_bricont", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "flag", TEX_NEGATIVE_BRICONT);
+	RNA_def_property_boolean_funcs(prop, NULL, "rna_Texture_use_negative_bricont_set");
+	RNA_def_property_ui_text(prop, "Allow negative values", "Don't clamp to zero brightness & contrast");
+	RNA_def_property_update(prop, 0, "rna_Texture_update");
 	
 	/* RGB Factor */
 	prop = RNA_def_property(srna, "factor_red", PROP_FLOAT, PROP_NONE);
Index: source/blender/render/intern/include/texture.h
===================================================================
--- source/blender/render/intern/include/texture.h	(revision 48705)
+++ source/blender/render/intern/include/texture.h	(working copy)
@@ -35,17 +35,22 @@
 
 #define BRICONT                                                               \
 	texres->tin= (texres->tin-0.5f) * tex->contrast+tex->bright-0.5f;         \
-	if(texres->tin < 0.0f)      texres->tin= 0.0f;                            \
-	else if(texres->tin > 1.0f) texres->tin= 1.0f;                            \
+	if( !tex->flag & TEX_NEGATIVE_BRICONT ) {                                 \
+	    if(texres->tin < 0.0f)      texres->tin= 0.0f;                        \
+	    else if(texres->tin > 1.0f) texres->tin= 1.0f;                        \
+	}                                                                         \
 
 #define BRICONTRGB                                                            \
 	texres->tr= tex->rfac*((texres->tr-0.5f)*tex->contrast+tex->bright-0.5f); \
-	if(texres->tr<0.0f) texres->tr= 0.0f;                                     \
+	if(texres->tr<0.0f && !(tex->flag & TEX_NEGATIVE_BRICONT))                \
+        texres->tr= 0.0f;                                                     \
 	texres->tg= tex->gfac*((texres->tg-0.5f)*tex->contrast+tex->bright-0.5f); \
-	if(texres->tg<0.0f) texres->tg= 0.0f;                                     \
+	if(texres->tg<0.0f && !(tex->flag & TEX_NEGATIVE_BRICONT))                \
+        texres->tg= 0.0f;                                                     \
 	texres->tb= tex->bfac*((texres->tb-0.5f)*tex->contrast+tex->bright-0.5f); \
-	if(texres->tb<0.0f) texres->tb= 0.0f;                                     \
-	if(tex->saturation != 1.0f) {                                             \
+	if(texres->tb<0.0f && !(tex->flag & TEX_NEGATIVE_BRICONT))                \
+        texres->tb= 0.0f;                                                     \
+	if(tex->saturation != 1.0f && !(tex->flag & TEX_NEGATIVE_BRICONT)) {      \
 		float _hsv[3];                                                        \
 		rgb_to_hsv(texres->tr, texres->tg, texres->tb,                        \
 		           _hsv, _hsv+1, _hsv+2);                                     \