diff --git a/funcs/classif.c b/funcs/classif.c
index eb6dc37..9e4fd60 100644
--- a/funcs/classif.c
+++ b/funcs/classif.c
@@ -21,9 +21,19 @@ float		range, dist, rgb[3], dr, dg, db;
 int		x, y, on, off;
 
 #if DEBUG_LEVEL
-fprintf(stderr, ">>> %s ( %p %p %f %d )\n", __func__, psrc, pdst, fval, notused);
+fprintf(stderr, ">>> %s ( %p %p %f %d )\n", __func__,
+					psrc, pdst, fval, notused);
 #endif
 
+if (FIMG_TYPE_RGB != psrc->type) {
+	fprintf(stderr, "%s: bad src type %d\n", __func__, psrc->type);
+	return -7;
+	}
+if (fimg_images_not_compatible(psrc, pdst)) {
+	fprintf(stderr, "%s: bad dst type %d\n", __func__, pdst->type);
+	return -8;
+	}
+
 /* calculer les amplitudes RGB de l'image source */
 fimg_get_minmax_rgb(psrc, minmax);
 delta[0] = minmax[1] - minmax[0];
diff --git a/funcs/contour2x2.c b/funcs/contour2x2.c
index 804a95c..0c3add9 100644
--- a/funcs/contour2x2.c
+++ b/funcs/contour2x2.c
@@ -32,6 +32,16 @@ int     tbl[] = 			/* deep magic inside */
 fprintf(stderr, ">>> %s ( %p %p %d )\n", __func__, psrc, pdst, reverse);
 #endif
 
+if (FIMG_TYPE_RGB != psrc->type) {
+	fprintf(stderr, "%s: bad src type %d\n", __func__, psrc->type);
+	return -7;
+	}
+if (fimg_images_not_compatible(psrc, pdst)) {
+	fprintf(stderr, "%s: bad dst type %d\n", __func__, pdst->type);
+	return -8;
+	}
+
+
 if (reverse) {
 	v1 = 0.0;	v2 = 1.0;
 	}
diff --git a/funcs/qsortrgb.c b/funcs/qsortrgb.c
index 6a1a96a..dd801f8 100644
--- a/funcs/qsortrgb.c
+++ b/funcs/qsortrgb.c
@@ -27,6 +27,15 @@ int		foo, szimg;
 fprintf(stderr, ">>> %s ( %p %p %d )\n", __func__, psrc, pdst, notused);
 #endif
 
+if (FIMG_TYPE_RGB != psrc->type) {
+	fprintf(stderr, "%s: bad src type %d\n", __func__, psrc->type);
+	return -7;
+	}
+if (fimg_images_not_compatible(psrc, pdst)) {
+	fprintf(stderr, "%s: bad dst type %d\n", __func__, pdst->type);
+	return -8;
+	}
+
 foo = fimg_copy_data(psrc, pdst);
 
 szimg = pdst->width * pdst->height;
@@ -44,7 +53,7 @@ typedef struct {
 	float	r, g, b;
 	} pix;
 
-static compare_b(const void *p1, const void *p2)
+static int compare_b(const void *p1, const void *p2)
 {
 pix	*s1, *s2;
 s1 = (pix *)p1;
@@ -62,6 +71,15 @@ float		rgb[3];
 fprintf(stderr, ">>> %s ( %p %p %d )\n", __func__, psrc, pdst, notused);
 #endif
 
+if (FIMG_TYPE_RGB != psrc->type) {
+	fprintf(stderr, "%s: bad src type %d\n", __func__, psrc->type);
+	return -7;
+	}
+if (fimg_images_not_compatible(psrc, pdst)) {
+	fprintf(stderr, "%s: bad dst type %d\n", __func__, pdst->type);
+	return -8;
+	}
+
 szimg = pdst->width * pdst->height;
 fprintf(stderr, "%s : %d pixels\n", __func__, szimg);