diff --git a/floatimg.h b/floatimg.h
index eacfa88..3e62026 100644
--- a/floatimg.h
+++ b/floatimg.h
@@ -63,7 +63,8 @@ void fimg_print_sizeof(void);
 void  fimg_printhead(FloatImg *h);
 int   fimg_describe(FloatImg *head, char *txt);
 char *fimg_str_type(int type);
-int   fimg_plot_rgb (FloatImg *head, int x, int y, float r, float g, float b);
+int   fimg_plot_rgb (FloatImg *head, int x, int y,
+					float r, float g, float b);
 int   fimg_get_rgb(FloatImg *head, int x, int y, float *rgb);
 int   fimg_put_rgb(FloatImg *head, int x, int y, float *rgb);
 int   fimg_clear(FloatImg *fimg);
@@ -119,6 +120,10 @@ int fimg_power_2(FloatImg *s, FloatImg *d, double maxval);
 int fimg_cos_01(FloatImg *s, FloatImg *d, double maxval);
 int fimg_cos_010(FloatImg *s, FloatImg *d, double maxval);
 
+
+int fimg_mix_rgb_gray(FloatImg *img, float mix);
+
+
 /*	module funcs/geometry.c		*/
 int fimg_equalize_compute(FloatImg *src, void *vptr);
 
diff --git a/funcs/Makefile b/funcs/Makefile
index 209947d..9ad28ab 100644
--- a/funcs/Makefile
+++ b/funcs/Makefile
@@ -4,7 +4,7 @@ COPT = -Wall -fpic -g -no-pie -DDEBUG_LEVEL=0
 DEPS = ../floatimg.h Makefile
 OBJS = fimg-png.o fimg-tiff.o misc-plots.o filtrage.o utils.o	\
 	fimg-libpnm.o rampes.o sfx0.o geometry.o rotate.o	\
-	equalize.o fimg-fits.o
+	equalize.o fimg-fits.o saturation.o
 
 #---------------------------------------------------------------
 
@@ -41,6 +41,9 @@ geometry.o:		geometry.c $(DEPS)
 rotate.o:		rotate.c $(DEPS)
 	gcc $(COPT) -c $<
 
+saturation.o:		saturation.c $(DEPS)
+	gcc $(COPT) -c $<
+
 equalize.o:		equalize.c $(DEPS)
 	gcc $(COPT) -c $<
 
diff --git a/funcs/saturation.c b/funcs/saturation.c
new file mode 100644
index 0000000..68ff388
--- /dev/null
+++ b/funcs/saturation.c
@@ -0,0 +1,44 @@
+/*
+ *	FloatImg library from tTh
+ */
+
+#include  <stdio.h>
+
+#include  "../floatimg.h"
+
+/* -------------------------------------------------------------- */
+/*	global vars from main
+ */
+extern	int	verbosity;
+
+/* -------------------------------------------------------------- */
+
+int fimg_mix_rgb_gray(FloatImg *img, float mix)
+{
+int		x, y, p;
+float		gr;
+
+if (FIMG_TYPE_RGB != img->type) {
+	fprintf(stderr, "%s bad type\n", __func__);
+	return -6;
+	}
+
+for (y=0; y<img->height; y++) {
+	p = y * img->width;
+	for (x=0; x<img->width; x++) {
+
+		gr = (img->R[p] + img->G[p] + img->R[p]) / 3.0;
+
+		img->R[p] = ((gr * mix) + (img->R[p] * (1.0-mix))) / 2.0;
+		img->G[p] = ((gr * mix) + (img->G[p] * (1.0-mix))) / 2.0;
+		img->B[p] = ((gr * mix) + (img->B[p] * (1.0-mix))) / 2.0;
+
+		p++;			/* next pixel in the row */
+		}
+
+	}
+
+return 0;
+}
+
+/* -------------------------------------------------------------- */