diff --git a/floatimg.h b/floatimg.h
index c59af44..3704e16 100644
--- a/floatimg.h
+++ b/floatimg.h
@@ -3,7 +3,7 @@
  *			ugly code from tTh
  */
 
-#define		FIMG_VERSION	106
+#define		FIMG_VERSION	107
 
 /*
  *	in memory descriptor
diff --git a/lib/fimg-2gray.c b/lib/fimg-2gray.c
index 02f66d6..4884b9e 100644
--- a/lib/fimg-2gray.c
+++ b/lib/fimg-2gray.c
@@ -70,7 +70,7 @@ for (foo=0; foo<nbb; foo++) {
 			(src->R[foo] + src->G[foo] + src->B[foo]) / 3.0;
 	}
 
-return -99;
+return 0;
 }
 /* --------------------------------------------------------------------- */
 
diff --git a/tools/cumulfimgs.c b/tools/cumulfimgs.c
index c89cd84..2baa54b 100644
--- a/tools/cumulfimgs.c
+++ b/tools/cumulfimgs.c
@@ -19,12 +19,12 @@ int		foo, numbers[3];
 foo = fimg_fileinfos(path, numbers);
 if (foo) {
 #if DEBUG_LEVEL
-	fprintf(stderr, "%s -> err %d\n", path, foo);
+	fprintf(stderr, "fileinfo of '%s' -> err %d\n", path, foo);
 #endif
 	return foo;
 	}
 
-fprintf(stderr, "%s \t%d x %d\n",path, numbers[0], numbers[1]);
+if (verbosity) fprintf(stderr, "%-20s %d x %d\n",path, numbers[0], numbers[1]);
 
 if (FIMG_TYPE_RGB != numbers[2]) {
 	fprintf(stderr, "file %s, %d : bad type\n", path, numbers[2]);
@@ -39,6 +39,7 @@ void help(int v)
 puts("cumulator options :");
 puts("\t-v\tincrease verbosity");
 puts("\t-o\tname of output file");
+puts("\t-g\tconvert to gray level");
 
 if (verbosity) { puts(""); fimg_print_version(1); }
 exit(0);
@@ -48,14 +49,17 @@ int main(int argc, char *argv[])
 {
 int		foo, idx;
 int		opt;
+
+int		to_gray = 0;
 char		*output_file = "out.fimg";
 FloatImg	accu, temp;
 int		src_loaded = 0;
 
 g_width = g_height = 0;
 
-while ((opt = getopt(argc, argv, "ho:v")) != -1) {
+while ((opt = getopt(argc, argv, "gho:v")) != -1) {
 	switch(opt) {
+		case 'g':	to_gray = 1;			break;
 		case 'h':	help(0);			break;
 		case 'o':	output_file = optarg;		break;
 		case 'v':	verbosity++;			break;
@@ -73,10 +77,14 @@ fprintf(stderr, "argc = %d, optind = %d\n", argc, optind);
 
 for (idx=optind; idx<argc; idx++) {
 
+#if DEBUG_LEVEL
 	fprintf(stderr, "%5d   %s\n", idx, argv[idx]);
+#endif
 
 	foo = testfile(argv[idx]);
-	fprintf(stderr, "testfile %s -> %d\n", argv[idx],foo);
+	if (foo) {
+		fprintf(stderr, "testfile %s -> %d\n", argv[idx],foo);
+		}
 
 	if ( ! src_loaded ) {
 		foo = fimg_create_from_dump(argv[idx], &accu);
@@ -85,12 +93,24 @@ for (idx=optind; idx<argc; idx++) {
 		}
 	else	{
 		foo = fimg_load_from_dump(argv[idx], &temp);
+		if (foo) {
+			fprintf(stderr, "load from dump -> %d\n", foo);
+			exit(1);
+			}
 		fimg_add_2(&temp, &accu);
 		}
 
 
 	}
 
+if (to_gray) {
+
+	foo = fimg_desaturate(&accu, &accu, 0);
+	if (foo) {
+		fprintf(stderr, "desaturate: error %d\n", foo);
+		}
+	}
+
 foo = fimg_dump_to_file(&accu, output_file, 0);
 
 return 0;
diff --git a/tools/essai.sh b/tools/essai.sh
index acd7d69..d0c69d1 100755
--- a/tools/essai.sh
+++ b/tools/essai.sh
@@ -37,7 +37,7 @@ D=" 800 600 "
 ./mkfimg -v -t vdeg	vdeg.fimg $D
 ./mkfimg -v -t drand48	rand.fimg $D
 
-./cumulfimgs -vv -o foo.fimg hdeg.fimg rand.fimg vdeg.fimg
+./cumulfimgs -v -g -o foo.fimg hdeg.fimg rand.fimg vdeg.fimg
 }
 #  -----------------------------------------------------