if (formatPtr == NULL) {
        if ((formatObj != NULL) && !matched) {
            Tcl_AppendResult(interp, "image format \"", formatString,
                    "\" is not supported", (char *) NULL);
        } else {
            Tcl_AppendResult(interp, "couldn't recognize image data",
                    (char *) NULL);
        }
        return TCL_ERROR;
    }