diff --git a/software/videomixer/main.c b/software/videomixer/main.c
index 203d69e20..aa92c0f87 100644
--- a/software/videomixer/main.c
+++ b/software/videomixer/main.c
@@ -25,20 +25,51 @@ static int scale_pot(int raw, int range)
 	return scaled;
 }
 
-static void pots_service(void)
+static void regular_blend(int p0, int p1)
 {
-	static int last_event;
 	int blackout;
 	int crossfade;
 
+	blackout = scale_pot(p0, 256);
+	crossfade = scale_pot(p1, 255);
+
+	fb_blender_f0_write(crossfade*blackout >> 8);
+	fb_blender_f1_write((255-crossfade)*blackout >> 8);	
+}
+
+static void additive_blend(int p0, int p1)
+{
+	fb_blender_f0_write(scale_pot(p0, 255));
+	fb_blender_f1_write(scale_pot(p1, 255));
+}
+
+static void pots_service(void)
+{
+	static int last_event;
+	static int additive_blend_enabled;
+	static int old_btn;
+	int btn;
+	int p0, p1;
+
 	if(elapsed(&last_event, identifier_frequency_read()/32)) {
+		btn = buttons_in_read() & 0x1;
+		if(btn && !old_btn) {
+			additive_blend_enabled = !additive_blend_enabled;
+			if(additive_blend_enabled)
+				leds_out_write(leds_out_read() | 0x1);
+			else
+				leds_out_write(leds_out_read() & ~0x1);
+		}
+		old_btn = btn;
+
 		pots_start_busy_write(1);
 		while(pots_start_busy_read());
-		blackout = scale_pot(pots_res0_read(), 256);
-		crossfade = scale_pot(pots_res1_read(), 255);
-
-		fb_blender_f0_write(crossfade*blackout >> 8);
-		fb_blender_f1_write((255-crossfade)*blackout >> 8);	
+		p0 = pots_res0_read();
+		p1 = pots_res1_read();
+		if(!additive_blend_enabled)
+			regular_blend(p0, p1);
+		else
+			additive_blend(p0, p1);
 	}
 }