introduction des ajustements de contraste

lib/fimg-2gray.c

@@ -33,6 +33,9 @@ if (FIMG_TYPE_RGB != src->type) {
 if (FIMG_TYPE_GRAY != dst->type) {
 	fprintf(stderr, "%s : bad dst type %d on %p\n", __func__, 
 				dst->type, dst);
+	/*
+	 * may be we can convert dst picture on the fly ?
+	 */
 	return -9;
 	}