file_gif.htm
来自「GIF解码以下是gif图形显示的源代码以下是gif图形显示的源代码」· HTM 代码 · 共 1,068 行 · 第 1/5 页
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...<br>
</td>
<td rowspan="3"><small>图象数据，由一个或几个数据块(</small><a
href="#数据块"><font SIZE="2">Data Sub-blocks</font></a><small>)组成</small></td>
</tr>
<tr>
<td colspan="8" align="center" bgcolor="#BDCB85"><br>
<small>数据块</small><br>
</td>
</tr>
<tr>
<td colspan="8" align="center" bgcolor="#BDCB85"><br>
<small>...</small><br>
</td>
</tr>
</table>
<p><small>GIF图象数据使用了LZW压缩算法（详细介绍请看后面的<a
href="#2.LZW算法和GIF数据压缩">『LZW算法和GIF数据压缩』</a>），大大减小了图象数据的大小。图象数据在压缩前有两种排列格式：<a
name="连续的和交织的">连续的和交织的</a>(由图象标识符的<a
href="#交织标志">交织标志</a>控制)。连续方式按从左到右、从上到下的顺序排列图象的光栅数据；交织图象按下面的方法处理光栅数据：</small></p>
<p><small>创建四个通道(pass)保存数据，每个通道提取不同行的数据：</small><br>
<small>第一通道(Pass 1)提取从第0行开始每隔8行的数据；</small><br>
<small>第二通道(Pass 2)提取从第4行开始每隔8行的数据；</small><br>
<small>第三通道(Pass 3)提取从第2行开始每隔4行的数据；</small><br>
<small>第四通道(Pass 4)提取从第1行开始每隔2行的数据；</small></p>
<p><small>下面的例子演示了提取交织图象数据的顺序：</small></p>
<table border="0" width="100%" cellspacing="0" cellpadding="0">
<tr>
<td align="center"><small>行</small></td>
<td align="center"><small> 通道1 </small></td>
<td align="center"><small> 通道2 </small></td>
<td align="center"><small> 通道3 </small></td>
<td align="center"><small> 通道4 </small></td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>0 --------------------------------------------------------</small></td>
<td align="center">1</td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>1 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">4</td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>2 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">3</td>
<td align="center"></td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>3 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">4</td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>4 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center">2</td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>5 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">4</td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>6 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">3</td>
<td align="center"></td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>7 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">4</td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>8 --------------------------------------------------------</small></td>
<td align="center">1</td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>9 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">4</td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>10 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">3</td>
<td align="center"></td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>11 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">4</td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>12 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center">2</td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>13 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">4</td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>14 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">3</td>
<td align="center"></td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>15 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">4</td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>16 --------------------------------------------------------</small></td>
<td align="center">1</td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>17 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">4</td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>18 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">3</td>
<td align="center"></td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>19 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
<td align="center">4</td>
<td align="center"></td>
</tr>
<tr>
<td align="center"><small>20 --------------------------------------------------------</small></td>
<td align="center"></td>
<td align="center">2</td>
<td align="center"></td>
<td align="center"></td>
<td align="center"></td>
</tr>
</table>
<p> </p>
<p><small>图形控制扩展(Graphic Control Extension)</small><br>
<font color="#FF0000"><small>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~</small><br>
</font><small>这一部分是可选的（需要89a版本），可以放在一个图象块(图象标识符)或文本扩展块的前面，用来控制跟在它后面的第一个图象（或文本）的渲染(Render)形式，组成结构如下：</small></p>
<table border="0" width="100%" cellpadding="0">
<tr>
<td align="right">BYTE</td>
<td align="center">7</td>
<td align="center">6</td>
<td align="center">5</td>
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