diff --git a/lib/fimg-math.c b/lib/fimg-math.c
index 33f6a43..50ecc0c 100644
--- a/lib/fimg-math.c
+++ b/lib/fimg-math.c
@@ -396,6 +396,8 @@ if (fi->type != FIMG_TYPE_RGB) {
 	return;
 	}
 nbre = fi->width * fi->height;
+// fprintf(stderr, "%s: %d pixels\n", __func__, nbre);
+
 for (idx=0; idx<nbre; idx++) {
 	fi->R[idx] = drand48() * kmul;
 	fi->G[idx] = drand48() * kmul;