上下两个表格之间为什么中间会有大约5象素的间距？

今天发现一个问题：上下两个表格中间有大约5象素的间距。
代码是这样的

<!--head-->
    <div align="center">
        <table width="778" border="0" cellpadding="0" cellspacing="0">
            <tr>
                <td>
                    <img src="images/head.gif"></td>
            </tr>
        </table>
    </div>
    <!--end head-->
    <!--menu-->
    <div align="center">
        <table width="778" border="0" cellpadding="0" cellspacing="0">
            <tr>
                <td>
                    <img src="images/menu_1.gif" width="8" height="37" alt=""></td>
                <td>
                    <img src="images/menu_2.gif" width="668" height="37" alt=""></td>
                <td>
                    <img src="images/menu_3.gif" width="13" height="37" alt=""></td>
                <td>
                    <img src="images/menu_4.gif" width="67" height="37" alt=""></td>
                <td>
                    <img src="images/menu_5.gif" width="22" height="37" alt=""></td>
            </tr>
        </table>
    </div>
    <!--end menu-->

最后经过调试，终于发现是因为head中image的宽度和高度没有设定。改成下面的代码即可。

<!--head-->
    <div align="center">
        <table width="778" border="0" cellpadding="0" cellspacing="0">
            <tr>
                <td>
                    <img src="images/head.gif" width="778" height="98" alt=""></td>
            </tr>
        </table>
    </div>
    <!--end head-->
    <!--menu-->
    <div align="center">
        <table width="778" border="0" cellpadding="0" cellspacing="0">
            <tr>
                <td>
                    <img src="images/menu_1.gif" width="8" height="37" alt=""></td>
                <td>
                    <img src="images/menu_2.gif" width="668" height="37" alt=""></td>
                <td>
                    <img src="images/menu_3.gif" width="13" height="37" alt=""></td>
                <td>
                    <img src="images/menu_4.gif" width="67" height="37" alt=""></td>
                <td>
                    <img src="images/menu_5.gif" width="22" height="37" alt=""></td>
            </tr>
        </table>
    </div>
    <!--end menu-->

如果还有间隔的话，把<td><img src="" width="" height=""></td> 中间不要留空格。