static struct rev_info *opt = &log_tree_opt;
        int read_stdin = 0;
 
-       git_config(git_diff_config);
+       git_config(git_default_config); /* no "diff" UI options */
        nr_sha1 = 0;
        init_revisions(opt);
        opt->abbrev = 0;
                usage(diff_tree_usage);
        }
 
+       if (!opt->diffopt.output_format)
+               opt->diffopt.output_format = DIFF_FORMAT_RAW;
+
        /*
         * NOTE! We expect "a ^b" to be equal to "a..b", so we
         * reverse the order of the objects if the second one