diff --git a/essai.c b/essai.c
index 08f4a3f..4f9b673 100644
--- a/essai.c
+++ b/essai.c
@@ -62,7 +62,7 @@ for (foo=0; foo<NBP; foo++) {
 		printf("%5d / %5d\n", foo, NBP);
 		}
 	fait_un_dessin(&fimgB);
-	fimg_add(&fimgA, &fimgB, &fimgA);
+	fimg_add_3(&fimgA, &fimgB, &fimgA);
 	// fimg_mul(&fimgA, &fimgB, &fimgA);
 	}
 tb = fimg_timer_get(0);
diff --git a/floatimg.h b/floatimg.h
index 2716bba..d4b91e4 100644
--- a/floatimg.h
+++ b/floatimg.h
@@ -2,7 +2,7 @@
  *	floatimg.h
  */
 
-#define		FIMG_VERSION	86
+#define		FIMG_VERSION	87
 
 /*
  *	in memory descriptor
@@ -69,9 +69,10 @@ int fimg_images_compatible(FloatImg *a, FloatImg *b);
 int fimg_interpolate(FloatImg *s1, FloatImg *s2, FloatImg *d, float coef);
 
 /*	'operats' module 		*/
-int fimg_add(FloatImg *a, FloatImg *b, FloatImg *d);
-int fimg_sub(FloatImg *a, FloatImg *b, FloatImg *d);
-int fimg_mul(FloatImg *a, FloatImg *b, FloatImg *d);
+int fimg_add_3(FloatImg *a, FloatImg *b, FloatImg *d);
+int fimg_add_2(FloatImg *a, FloatImg *b);			/* B+=A */
+int fimg_sub_3(FloatImg *a, FloatImg *b, FloatImg *d);
+int fimg_mul_3(FloatImg *a, FloatImg *b, FloatImg *d);
 int fimg_minimum(FloatImg *a, FloatImg *b, FloatImg *d);
 int fimg_maximum(FloatImg *a, FloatImg *b, FloatImg *d);
 
diff --git a/lib/operators.c b/lib/operators.c
index ef75e8e..cd703d2 100644
--- a/lib/operators.c
+++ b/lib/operators.c
@@ -16,10 +16,10 @@ extern int verbosity;		/* must be declared around main() */
 
 /* ---------------------------------------------------------------- */
 /*
- * 	A + B -> D
+ * 		A + B -> D
  * 				why is this func so slow ?
  */
-int fimg_add(FloatImg *a, FloatImg *b, FloatImg *d)
+int fimg_add_3(FloatImg *a, FloatImg *b, FloatImg *d)
 {
 int		idx, nbpixels;
 
@@ -40,13 +40,40 @@ for (idx=0; idx<nbpixels; idx++) {
 	d->B[idx] = a->B[idx] + b->B[idx];
 	}
 
+return 0;
+}
+/* ---------------------------------------------------------------- */
+/*
+ * 		B += A		may be faster than fimg_add_3 ?
+ */
+int fimg_add_2(FloatImg *a, FloatImg *b)
+{
+int		idx, nbpixels;
+
+#if DEBUG_LEVEL
+fprintf(stderr, ">>> %s ( %p %p )\n", __func__, a, b);
+#endif
+
+if (3 != a->type || 3 != b->type) {
+	fprintf(stderr, "%s : got a bad type fimg\n", __func__);
+	return -8;
+	}
+
+nbpixels = a->width * a->height;
+
+for (idx=0; idx<nbpixels; idx++) {
+	b->R[idx] += a->R[idx];
+	b->G[idx] += a->G[idx];
+	b->B[idx] += a->B[idx];
+	}
+
 return 0;
 }
 /* ---------------------------------------------------------------- */
 /*
  *		A - B -> D
  */
-int fimg_sub(FloatImg *a, FloatImg *b, FloatImg *d)
+int fimg_sub_3(FloatImg *a, FloatImg *b, FloatImg *d)
 {
 int		idx, nbpixels;
 
@@ -57,7 +84,7 @@ fprintf(stderr, ">>> %s ( %p %p %p )\n", __func__, a, b, d);
 if (3 != a->type || 3 != b->type || 3 != d->type) {
 	fprintf(stderr, "%s : got a bad type fimg\n", __func__);
 	return -8;
-	} 
+	}
 
 nbpixels = a->width * a->height;
 
@@ -76,7 +103,7 @@ return 0;
 /*
  *		A * B -> D
  */
-int fimg_mul(FloatImg *a, FloatImg *b, FloatImg *d)
+int fimg_mul_3(FloatImg *a, FloatImg *b, FloatImg *d)
 {
 int		idx, nbpixels;
 
diff --git a/tools/fimgops.c b/tools/fimgops.c
index a9359bb..e7420fc 100644
--- a/tools/fimgops.c
+++ b/tools/fimgops.c
@@ -80,16 +80,16 @@ int	foo;
 switch (action)	{
 
 	case OP_ADD:
-		foo = fimg_add(A, B, D);		break;
+		foo = fimg_add_3(A, B, D);		break;
 	case OP_SUB:
-		foo = fimg_sub(A, B, D);		break;
+		foo = fimg_sub_3(A, B, D);		break;
 	case OP_MIX:
 		if (verbosity) fprintf(stderr, "fvalue is %f\n",
 							global_fvalue);
 		foo = fimg_interpolate(A, B, D, global_fvalue);
 		break;
 	case OP_MUL:
-		foo = fimg_add(A, B, D);		break;
+		foo = fimg_mul_3(A, B, D);		break;
 	case OP_MINI:
 		foo = fimg_maximum(A, B, D);		break;
 	case OP_MAXI: