diff --git a/lib/Makefile b/lib/Makefile
index 4980a4c..ea2e3d4 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -5,7 +5,7 @@
 COPT = -Wall -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
+	interpolate.o fimg-compare.o contrast.o
 
 DEPS = Makefile ../floatimg.h
 
@@ -34,6 +34,9 @@ fimg-2gray.o:	fimg-2gray.c $(DEPS)
 operators.o:	operators.c $(DEPS)
 	gcc $(COPT) -c $<
 
+contrast.o:	contrast.c $(DEPS)
+	gcc $(COPT) -c $<
+
 interpolate.o:	interpolate.c $(DEPS)
 	gcc $(COPT) -c $<
 
diff --git a/lib/contrast.c b/lib/contrast.c
new file mode 100644
index 0000000..09dff29
--- /dev/null
+++ b/lib/contrast.c
@@ -0,0 +1,64 @@
+#include  <stdio.h>
+#include  <stdlib.h>
+#include  <unistd.h>
+#include  <string.h>
+#include  <math.h>
+
+#include  "../floatimg.h"
+
+extern int		verbosity;
+
+/* ---------------------------------------------------------------- */
+int fimg_square_root(FloatImg *s, FloatImg *d, double maxval)
+{
+int		nbre, idx;
+double		dval;
+
+if (s->type != FIMG_TYPE_RGB) {
+	fprintf(stderr, "%s : type %d invalide\n",
+				__func__, s->type);
+	return -4;
+	}
+
+if (NULL==d) {
+	d = s;
+	}
+
+
+nbre = s->width * s->height * 3;
+
+for (idx=0; idx<nbre; idx++) {
+	dval = s->R[idx] / maxval;
+	d->R[idx] = maxval * sqrt(dval);
+	}
+
+return -1;
+}
+/* ---------------------------------------------------------------- */
+int fimg_power_2(FloatImg *s, FloatImg *d, double maxval)
+{
+int		nbre, idx;
+double		dval;
+
+if (s->type != FIMG_TYPE_RGB) {
+	fprintf(stderr, "%s : type %d invalide\n",
+				__func__, s->type);
+	return -4;
+	}
+
+if (NULL==d) {
+	d = s;
+	}
+
+
+nbre = s->width * s->height * 3;
+
+for (idx=0; idx<nbre; idx++) {
+	dval = s->R[idx] / maxval;
+	d->R[idx] = maxval * dval * dval;
+	}
+
+return -1;
+}
+
+/* ---------------------------------------------------------------- */
diff --git a/lib/t.c b/lib/t.c
index f2a0eb2..6534d76 100644
--- a/lib/t.c
+++ b/lib/t.c
@@ -67,71 +67,53 @@ fimg_destroy(&gray);
 return 0;
 }
 /* ---------------------------------------------------------------- */
-/****
-foo = fimg_create(&dessin, W, H, 3);
-petit_dessin(&dessin);
-foo = fimg_create(&noise, W, H, 3);
-fimg_drand48(&noise, 0.1);
-****/
+
+int fimg_square_root(FloatImg *s, FloatImg *d, double maxval);
+int fimg_power_2(FloatImg *s, FloatImg *d, double maxval);
+
+int essai_contraste(char *fname)
+{
+int		foo;
+FloatImg 	dessin;
+double		maxi;
+
+foo = fimg_create_from_dump(fname, &dessin);
+
+maxi = (double)fimg_get_maxvalue(&dessin);
+fprintf(stderr, "avant    valeur maxi = %f\n", maxi);
+
+fimg_power_2(&dessin, NULL, maxi);
+
+maxi = (double)fimg_get_maxvalue(&dessin);
+fprintf(stderr, "apres    valeur maxi = %f\n", maxi);
+
+fimg_dump_to_file(&dessin, "dst.fimg", 0);
+
+fimg_destroy(&dessin);
+
+return -1;
+}
 /* ---------------------------------------------------------------- */
 #define W 320
 #define H 240
 int main(int argc, char *argv[])
 {
 int		foo, idx, opt;
-float		coef;
-FloatImg 	dessin, noise, result;
-char		outname[100];
+// char		outname[100];
 int		gray = 0;
-int		nb_img = 42;
 
 while ((opt = getopt(argc, argv, "gn:v")) != -1) {
 	switch(opt) {
 		case 'g':	gray++;			break;
-		case 'n':	nb_img=atoi(optarg);	break;
+		case 'n':	foo=atoi(optarg);	break;
 		case 'v':	verbosity++;		break;
 		}
 	}
 
 if (verbosity) fimg_print_version(0);
 
+foo = essai_contraste("src.fimg");
 
-foo = fimg_create_from_png("/home/tth/TMP/floatimg/s1.png", &dessin);
-if (foo) {
-	fprintf(stderr, "s1 load err %d\n", foo);
-	exit(1);
-	}
-if (verbosity) fimg_describe(&dessin, "s1 dessin");
-if (gray) fimg_to_gray(&dessin);
-
-foo = fimg_create_from_png("/home/tth/TMP/floatimg/s2.png", &noise);
-if (foo) {
-	fprintf(stderr, "s2 load err %d\n", foo);
-	exit(1);
-	}
-if (verbosity) fimg_describe(&noise, "s2 noise");
-fimg_mul_cste(&noise, 0.50);
-if (gray) fimg_to_gray(&noise);
-
-foo = fimg_create(&result, W, H, 3);
-if (verbosity) fimg_describe(&result, "d result");
-
-fprintf(stderr, "running for %d picz\n", nb_img);
-
-for (idx=0; idx<nb_img; idx++) {
-
-	coef = (float)idx / (float)nb_img;
-	// coef = (0.5-0.5*cos(4*3.141592654*coef));
-
-	foo = fimg_interpolate(&dessin, &noise, &result, coef);
-	printf("%6d    %9.6f\n", idx, coef);
-
-	sprintf(outname, "/home/tth/TMP/floatimg/%05d.pnm", idx);
-	foo = fimg_save_as_pnm(&result, outname, 0);
-	}
-
-/* yes, we can cleanup after work */
-fimg_destroy(&dessin), fimg_destroy(&noise), fimg_destroy(&result);
 
 return 0;
 }