diff --git a/lib/Makefile b/lib/Makefile
index 3ffea72e..9fadac31 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -7,7 +7,7 @@ COPT = -Wall -Wextra -fpic -g   -no-pie -DDEBUG_LEVEL=0
 OBJS = fimg-core.o fimg-pnm.o fimg-file.o fimg-math.o	\
 	fimg-timers.o operators.o fimg-2gray.o		\
 	interpolate.o fimg-compare.o contrast.o		\
-	metadata.o
+	metadata.o alphachan.o
 
 DEPS = Makefile ../floatimg.h
 
@@ -24,6 +24,9 @@ t:	t.c ../libfloatimg.a $(DEPS)
 ../libfloatimg.a:	$(OBJS)
 	$(AR) r $@ $?
 
+alphachan.o:	alphachan.c $(DEPS)
+	gcc $(COPT) -c $<
+
 fimg-core.o:	fimg-core.c $(DEPS)
 	gcc $(COPT) -c $<
 
diff --git a/lib/README.md b/lib/README.md
index ee05c620..1f9bb6bf 100644
--- a/lib/README.md
+++ b/lib/README.md
@@ -2,3 +2,7 @@
 
 Need more explanations...
 
+
+
+## Converting to/from rgb or gray 
+
diff --git a/lib/alphachan.c b/lib/alphachan.c
new file mode 100644
index 00000000..0ceee386
--- /dev/null
+++ b/lib/alphachan.c
@@ -0,0 +1,23 @@
+/*
+ *              alphachan.c
+ */
+
+#include  <stdio.h>
+#include  <stdint.h>
+#include	<sys/time.h>
+
+#include  "../floatimg.h"
+
+extern int verbosity;           /* must be declared around main() */
+
+/* ---------------------------------------------------------------- */
+int fimg_add_alpha_chan(FloatImg *img)
+{
+return -4;
+}
+/* ---------------------------------------------------------------- */
+int fimg_kill_alpha_chan(FloatImg *img)
+{
+return -4;
+}
+/* ---------------------------------------------------------------- */
diff --git a/lib/fimg-2gray.c b/lib/fimg-2gray.c
index 948d3d0e..a83d7144 100644
--- a/lib/fimg-2gray.c
+++ b/lib/fimg-2gray.c
@@ -1,5 +1,7 @@
 /*
  *		fimg-2gray.c
+ *
+ *	This is a tricky job...
  */
 
 #include  <stdio.h>
@@ -29,7 +31,6 @@ else	{
 	/* ... and canonic random values */
 	kr = kg = kb = 1.0;
 	}
-
 kdiv = kr + kg + kb;
 
 /* we must check the validity of our parameters */
diff --git a/lib/t.c b/lib/t.c
index 6a4b8625..4ec094b8 100644
--- a/lib/t.c
+++ b/lib/t.c
@@ -86,6 +86,11 @@ fprintf(stderr, "   %f      %f\n", A, B);
 return 0;
 }
 /* ---------------------------------------------------------------- */
+int essai_alphachan(void)
+{
+
+return -1984;
+}
 /* ---------------------------------------------------------------- */
 #define  WI	1024
 #define  HI	768
diff --git a/tools/cumulfimgs.c b/tools/cumulfimgs.c
index bd086a1e..26efa200 100644
--- a/tools/cumulfimgs.c
+++ b/tools/cumulfimgs.c
@@ -1,5 +1,6 @@
 /*
  *		This thing is just a mess !
+ *		***************************
  */
 #include  <stdio.h>
 #include  <stdlib.h>
@@ -103,15 +104,19 @@ for (idx=optind; idx<argc; idx++) {
 	compte++;
 	}
 
-/*			XXX */
+/*		XXX */
 if (experiment) {
 
 		}
-/*			XXX */
+/*		XXX */
 
 
 if (to_gray) {
 	foo = fimg_desaturate(&accu, &accu, 0);
+	/* ?
+	 * but here, final picture is in RGB shape, so export give us
+	 * also an image rgb-shaped. this is not optimal, I think.
+	 */
 	if (foo) {
 		fprintf(stderr, "desaturate: error %d\n", foo);
 		}