diff --git a/funcs/filtrage.c b/funcs/filtrage.c
index 732c3037..2d7100cd 100644
--- a/funcs/filtrage.c
+++ b/funcs/filtrage.c
@@ -19,6 +19,11 @@ fprintf(stderr,"     type %d size %dx%d\n", img->type,
 					img->width, img->height);
 #endif
 
+if (img->type != FIMG_TYPE_RGB) {
+	fprintf(stderr, "%s : type %d invalide\n", __func__, img->type);
+	return -99;
+	}
+
 pr = img->R;	pg = img->G;	pb = img->B;
 
 for (y=1; y < img->height-1; y++) {
@@ -56,6 +61,12 @@ fprintf(stderr,"     type %d size %dx%d\n", img->type,
 					img->width, img->height);
 #endif
 
+if (img->type != FIMG_TYPE_RGB) {
+	fprintf(stderr, "%s : type %d invalide\n", __func__, img->type);
+	return -99;
+	}
+
+
 h = img->height;	w = img->width;
 
 for (idx=0; idx<h; idx++) {