diff --git a/solidify/Makefile b/solidify/Makefile
index 4e021b9..ab6ef27 100644
--- a/solidify/Makefile
+++ b/solidify/Makefile
@@ -1,7 +1,7 @@
 CFLAGS=-Wall -g `pkg-config --cflags gtk+-2.0`
 LDFLAGS=-lm `pkg-config --libs gtk+-2.0`
 
-OBJS=array.o face.o level.o solidify.o
+OBJS=array.o face.o histo.o level.o solidify.o
 
 .PHONY:		all clean
 
diff --git a/solidify/face.c b/solidify/face.c
index 2f52f89..d057ba6 100644
--- a/solidify/face.c
+++ b/solidify/face.c
@@ -5,6 +5,7 @@
 
 #include "util.h"
 #include "array.h"
+#include "histo.h"
 #include "face.h"
 
 
@@ -12,13 +13,32 @@ struct face *read_face(const char *name)
 {
 	FILE *file;
 	struct face *f;
+	struct histo *h;
 	float x, y, z;
 	int xi, yi, zi;
 
-	file = strcmp(name, "-") ? fopen(name, "r") : stdin;
-	if (!file) {
-		perror(name);
-		exit(1);
+	if (!strcmp(name, "-")) {
+		file = stdin;
+	} else {
+		int len;
+
+		len = strlen(name);
+		if (len > 4 && !strcmp(name+len-4, ".bz2")) {
+			char tmp[1000]; /* @@@ enough */
+
+			sprintf(tmp, "bzcat \"%s\"", name);
+			file = popen(tmp, "r");
+			if (!file) {
+				perror(tmp);
+				exit(1);
+			}
+		} else {
+			file = fopen(name, "r");
+			if (!file) {
+				perror(name);
+				exit(1);
+			}
+		}
 	}
 	f = alloc_type(struct face);
 	f->a = new_array();
@@ -30,11 +50,14 @@ struct face *read_face(const char *name)
 		zi = round(z*40.0);
 		set(f->a, xi, yi, zi);
 	}
-	(void) fclose(file);
+	if (file != stdin)
+		(void) fclose(file);
 
 	f->sx = f->a->max_x-f->a->min_x+1;
 	f->sy = f->a->max_y-f->a->min_y+1;
-	f->z_ref = (f->a->min_z+f->a->max_z)/2;
+	h = make_histo(f->a);
+	f->z_ref = f->a->min_z+median(h);
+	free_histo(h);
 	fprintf(stderr, "%d-%d / %d-%d / %d-%d\n",
 	    f->a->min_x, f->a->max_x, f->a->min_y, f->a->max_y,
 	    f->a->min_z, f->a->max_z);
diff --git a/solidify/histo.c b/solidify/histo.c
new file mode 100644
index 0000000..c1e9153
--- /dev/null
+++ b/solidify/histo.c
@@ -0,0 +1,39 @@
+#include "util.h"
+#include "array.h"
+#include "histo.h"
+
+
+struct histo *make_histo(struct array *a)
+{
+	int i;
+	struct histo *h;
+
+	h = alloc_type(struct histo);
+	h->n = a->max_z-a->min_z+1;
+	h->b = alloc_size(h->n*sizeof(int));
+	for (i = 0; i != h->n; i++)
+		h->b[i] = 0;
+	for (i = 0; i != (a->max_x-a->min_x+1)*(a->max_y-a->min_y+1); i++)
+		if (a->data[i] != UNDEF)
+			h->b[a->data[i]-a->min_z]++;
+	return h;
+}
+
+
+void free_histo(struct histo *h)
+{
+	free(h);
+}
+
+
+int median(const struct histo *h)
+{
+	int tot = 0, sum = 0;
+	int i;
+
+	for (i = 0; i != h->n; i++)
+		tot += h->b[i];
+	for (i = 0; sum < tot/2; i++)
+		sum += h->b[i];
+	return i-1;
+}
diff --git a/solidify/histo.h b/solidify/histo.h
new file mode 100644
index 0000000..cef3c9b
--- /dev/null
+++ b/solidify/histo.h
@@ -0,0 +1,17 @@
+#ifndef HISTO_H
+#define HISTO_H
+
+#include "array.h"
+
+
+struct histo {
+	int n;	/* number of bins */
+	int *b; /* bins */
+};
+
+
+struct histo *make_histo(struct array *a);
+void free_histo(struct histo *h);
+int median(const struct histo *h);
+
+#endif /* HISTO_H */