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📁 数字图像处理入门. 一位图像处理高手写的书. 从图像处理的最基础开始,然后慢慢以一些例子做说明,进入图像处理的更高阶段.学习图像处理不可多得的比较朴实的书
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  </div>
  <p style='line-height:18.0pt'><span
style='font-family:宋体;"Times New Roman"'>你大概已经明白了，当一幅图中每个象素赋予不同的</span><span lang=EN-US>RGB</span><span
style='font-family:宋体;"Times New Roman"'>值时，能呈现出五彩缤纷的颜色了，这样就形成了彩色图。的确是这样的，但实际上的做法还有些差别。</span></p>
  <p style='line-height:18.0pt'><span
style='font-family:宋体;"Times New Roman"'>让我们来看看下面的例子。</span></p>
  <p style='line-height:18.0pt'><span
style='font-family:宋体;"Times New Roman"'>有一个长宽各为</span><span lang=EN-US>200</span><span
style='font-family:宋体;"Times New Roman"'>个象素，颜色数为</span><span lang=EN-US>16</span><span
style='font-family:宋体;"Times New Roman"'>色的彩色图，每一个象素都用</span><span lang=EN-US>R</span><span
style='font-family:宋体;"Times New Roman"'>、</span><span lang=EN-US>G</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>、</span><span
lang=EN-US>B</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>三个分量表示。因为每个分量有</span><span lang=EN-US>256</span><span
style='font-family:宋体;"Times New Roman"'>个级别，要用</span><span lang=EN-US>8</span><span
style='font-family:宋体;"Times New Roman"'>位</span><span lang=EN-US>(bit)</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>，即一个字节</span><span
lang=EN-US>(byte)</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>来表示，所以每个象素需要用</span><span lang=EN-US>3</span><span
style='font-family:宋体;"Times New Roman"'>个字节。整个图象要用</span><span lang=EN-US>200×200×3</span><span
style='font-family:宋体;"Times New Roman"'>，约</span><span lang=EN-US>120k</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>字节，可不是一个小数目呀！如果我们用下面的方法，就能省的多。</span></p>
  <p style='line-height:18.0pt'><span
style='font-family:宋体;"Times New Roman"'>因为是一个</span><span lang=EN-US>16</span><span
style='font-family:宋体;"Times New Roman"'>色图，也就是说这幅图中最多只有</span><span lang=EN-US>16</span><span
style='font-family:宋体;"Times New Roman"'>种颜色，我们可以用一个表：表中的每一行记录一种颜色的</span><span lang=EN-US>R</span><span
style='font-family:宋体;"Times New Roman"'>、</span><span lang=EN-US>G</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>、</span><span
lang=EN-US>B</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>值。这样当我们表示一个象素的颜色时，只需要指出该颜色是在第几行，即该颜色在表中的索引值。举个例子，如果表的第</span><span
lang=EN-US>0</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>行为</span><span lang=EN-US>255</span><span
style='font-family:宋体;"Times New Roman"'>，</span><span lang=EN-US>0</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>，</span><span
lang=EN-US>0(</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>红色</span><span lang=EN-US>)</span><span
style='font-family:宋体;"Times New Roman"'>，那么当某个象素为红色时，只需要标明</span><span lang=EN-US>0</span><span
style='font-family:宋体;"Times New Roman"'>即可。</span></p>
  <p style='line-height:18.0pt'><span
style='font-family:宋体;"Times New Roman"'>让我们再来计算一下：</span><span lang=EN-US>16</span><span
style='font-family:宋体;"Times New Roman"'>种状态可以用</span><span lang=EN-US>4</span><span
style='font-family:宋体;"Times New Roman"'>位</span><span lang=EN-US>(bit)</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>表示，所以一个象素要用半个字节。整个图象要用</span><span
lang=EN-US>200×200×0.5</span><span style='font-family:宋体;"Times New Roman";"Times New Roman"'>，约</span><span
lang=EN-US>20k</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>字节，再加上表占用的字节为</span><span lang=EN-US>3×16=48</span><span
style='font-family:宋体;"Times New Roman"'>字节</span><span lang=EN-US>.</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>整个占用的字节数约为前面的</span><span
lang=EN-US>1/6</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>，省很多吧？</span></p>
  <p style='line-height:18.0pt'><span
style='font-family:宋体;"Times New Roman"'>这张</span><span lang=EN-US>R</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>、</span><span
lang=EN-US>G</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>、</span><span lang=EN-US>B</span><span
style='font-family:宋体;"Times New Roman"'>的表，就是我们常说的调色板</span><span lang=EN-US>(Palette)</span><span
style='font-family:宋体;"Times New Roman"'>，另一种叫法是颜色查找表</span><span lang=EN-US>LUT(Look      
    Up Table)</span><span     
style='font-family:宋体;"Times New Roman"'>，似乎更确切一些。</span><span lang=EN-US>Windows</span><span
style='font-family:宋体;"Times New Roman"'>位图中便用到了调色板技术。其实不光是</span><span lang=EN-US>Windows</span><span
style='font-family:宋体;"Times New Roman"'>位图，许多图象文件格式如</span><span lang=EN-US>pcx</span><span
style='font-family:宋体;"Times New Roman"'>、</span><span lang=EN-US>tif</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>、</span><span
lang=EN-US>gif</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>等都用到了。所以很好地掌握调色板的概念是十分有用的。</span></p>
  <p style='line-height:18.0pt'><span
style='font-family:宋体;"Times New Roman"'>有一种图，它的颜色数高达</span><span lang=EN-US>256×256×256</span><span
style='font-family:宋体;"Times New Roman"'>种，也就是说包含我们上述提到的</span><span lang=EN-US>R</span><span
style='font-family:宋体;"Times New Roman"'>、</span><span lang=EN-US>G</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>、</span><span
lang=EN-US>B</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>颜色表示方法中所有的颜色，这种图叫做真彩色图</span><span
lang=EN-US>(true color)</span><span style='font-family:宋体;"Times New Roman";"Times New Roman"'>。真彩色图并不是说一幅图包含了所有的颜色，而是说它具有显示所有颜色的能力，即最多可以包含所有的颜色。表示真彩色图时，每个象素直接用</span><span     
lang=EN-US>R</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>、</span><span lang=EN-US>G</span><span
style='font-family:宋体;"Times New Roman"'>、</span><span lang=EN-US>B</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>三个分量字节表示，而不采用调色板技术。原因很明显：如果用调色板，表示一个象素也要用</span><span
lang=EN-US>24</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>位，这是因为每种颜色的索引要用</span><span
lang=EN-US>24</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>位</span><span lang=EN-US>(</span><span
style='font-family:宋体;"Times New Roman"'>因为总共有</span><span lang=EN-US>2<sup>24</sup></span><span
style='font-family:宋体;"Times New Roman"'>种颜色，即调色板有</span><span lang=EN-US>2<sup>24</sup></span><span
style='font-family:宋体;"Times New Roman"'>行</span><span lang=EN-US>)</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>，和直接用</span><span
lang=EN-US>R</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>，</span><span lang=EN-US>G</span><span
style='font-family:宋体;"Times New Roman"'>，</span><span lang=EN-US>B</span><span style='font-family:
宋体;&quot;Times New Roman&quot;'>三个分量表示用的字节数一样，不但没有任何便宜，还要加上一个</span><span
lang=EN-US>256×256×256×3</span><span style='font-family:宋体;"Times New Roman";"Times New Roman"'>个字节的大调色板。所以真彩色图直接用</span><span
lang=EN-US>R</span><span style='font-family:宋体;
&quot;Times New Roman&quot;'>、</span><span lang=EN-US>G</span><span
style='font-family:宋体;"Times New Roman"'>、</span><span lang=EN-US>B</span><span style='font-family:
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