OpenCV保存成XML（FileStorage）和CSV（重载<<运算符）文

XML文件（使用FileStorage类）

使用OpenCV时不仅要保存影像结果，往往也需要保存中间的矩阵结果，而OpenCV的imwrite函数只支持CV8U类型的数据（使用OpenCV保存其他类型Mat的时候，程序不会报错，但是无法生成结果文件），因此会给工作带来很多不便。OpenCV在2.0以后的版本中提供了FileStorage类，供用户直接使用，保存为XML/YAML文件。

保存XML

保存示例如下：

<code class="language-c++ hljs lasso has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro',monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">Mat mat <span class="hljs-subst" style="color: rgb(0,0); box-sizing: border-box;">=</span> Mat<span class="hljs-tag" style="color: rgb(0,102); box-sizing: border-box;">::eye</span>(Size(<span class="hljs-number" style="color: rgb(0,102); box-sizing: border-box;">12</span>,<span class="hljs-number" style="color: rgb(0,102); box-sizing: border-box;">12</span>),CV_8UC1);
FileStorage fs(<span class="hljs-string" style="color: rgb(0,136,0); box-sizing: border-box;">"f:vocabulary.xml"</span>,FileStorage<span class="hljs-tag" style="color: rgb(0,102); box-sizing: border-box;">::WRITE</span>);
fs <span class="hljs-subst" style="color: rgb(0,0); box-sizing: border-box;"><<</span> <span class="hljs-string" style="color: rgb(0,0); box-sizing: border-box;">"vocabulary"</span> <span class="hljs-subst" style="color: rgb(0,0); box-sizing: border-box;"><<</span> mat;
fs<span class="hljs-built_in" style="color: rgb(102,102); box-sizing: border-box;">.</span>release();</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238,238,238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221,221,221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

得到结果文件如下所示：

<code class="language-xml hljs  has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro',monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-pi" style="color: rgb(0,102); box-sizing: border-box;"><?xml version="1.0"?></span>
<span class="hljs-tag" style="color: rgb(0,102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0,136);">opencv_storage</span>></span>
<span class="hljs-tag" style="color: rgb(0,136);">vocabulary</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102,102);">type_id</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0,0);">"opencv-matrix"</span>></span>
  <span class="hljs-tag" style="color: rgb(0,136);">rows</span>></span>12<span class="hljs-tag" style="color: rgb(0,102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0,136);">rows</span>></span>
  <span class="hljs-tag" style="color: rgb(0,136);">cols</span>></span>12<span class="hljs-tag" style="color: rgb(0,136);">cols</span>></span>
  <span class="hljs-tag" style="color: rgb(0,136);">dt</span>></span>u<span class="hljs-tag" style="color: rgb(0,136);">dt</span>></span>
  <span class="hljs-tag" style="color: rgb(0,136);">data</span>></span>
    1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0
    0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0
    0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0
    0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0
    0 0 0 0 0 0 0 1<span class="hljs-tag" style="color: rgb(0,136);">data</span>></span><span class="hljs-tag" style="color: rgb(0,136);">vocabulary</span>></span>
<span class="hljs-tag" style="color: rgb(0,136);">opencv_storage</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238,221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li></ul>

需要注意的是，因为保存的结果为xml文件，所以再保存的时候需要给定标签，格式就是下面的形式，先存储标签内容，再存储矩阵：

<code class="language-c++ hljs bash has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro',monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">fs << <span class="hljs-string" style="color: rgb(0,0); box-sizing: border-box;">"vocabulary"</span> << mat;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238,221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

读取XML

同样使用FileStorage类可以直接获取保存的xml文件内容。
读取示例如下：

<code class="language-c++ hljs scss has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro',monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">FileStorage <span class="hljs-function" style="box-sizing: border-box;">fs(<span class="hljs-string" style="color: rgb(0,0); box-sizing: border-box;">".vocabulary.xml"</span>,FileStorage::READ)</span>;
Mat mat_vocabulary;
fs<span class="hljs-attr_selector" style="color: rgb(0,0); box-sizing: border-box;">["vocabulary"]</span> >> mat_vocabulary;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238,221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

读取文件的时候同样要给定标签内容，这里通过中括号[]给定：

 
 
CSV文件
 
 
很多时候，直接使用CSV文件相比XML更方便，使用XML保存得到的数据，无论是查看（excel查看，XML中矩阵不是格式化的）还是接着使用别的工具处理（例如matlab），都可以快速的读取，而XML需要解析则比较繁琐。那么该如何保存CSV文件呢，对保存的CSV文件又应该如何读取呢，请看下文分解。
 
 
保存CSV文件
 
 
OpenCV提供了结果保存的格式化函数format，使用format我们就可以根据自己想要的格式打印和保存数据了。
 
 
先直接看保存函数，再来分析具体含义吧：
 
 
<code class="language-c++ hljs mel has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro',monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">ofstream <span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">file</span>(<span class="hljs-string" style="color: rgb(0,0); box-sizing: border-box;">"test.csv"</span>);
<span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">file</span> << <span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">format</span>(mat,Formatter::FMT_CSV);
<span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">file</span>.close();</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238,221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>
 
 
根据上面的代码只用ofstream对象打开要写入的csv文件，再直接写入数据即可，需要注意的是，接入的矩阵用format格式化，format函数第二个参数表示格式类型，这里选择CSV格式即Formatter::FMT_CSV。
 
 
保存结果如图所示：
 
 
 
这里保存格式为定义在Formatter类中的枚举类型，总共有6中选项，各位读者可以根据自己的需求选择。
 
 
<code class="language-c++ hljs cs has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro',monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">class CV_EXPORTS Formatter
{
<span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">public</span>:
    <span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">enum</span> { FMT_DEFAULT = <span class="hljs-number" style="color: rgb(0,102); box-sizing: border-box;">0</span>,FMT_MATLAB  = <span class="hljs-number" style="color: rgb(0,102); box-sizing: border-box;">1</span>,FMT_CSV     = <span class="hljs-number" style="color: rgb(0,102); box-sizing: border-box;">2</span>,FMT_PYTHON  = <span class="hljs-number" style="color: rgb(0,102); box-sizing: border-box;">3</span>,FMT_NUMPY   = <span class="hljs-number" style="color: rgb(0,102); box-sizing: border-box;">4</span>,FMT_C       = <span class="hljs-number" style="color: rgb(0,102); box-sizing: border-box;">5</span>
         };

    <span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">virtual</span> ~Formatter();

    <span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">virtual</span> Ptr<Formatted> format(<span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">const</span> Mat& mtx) <span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">const</span> = <span class="hljs-number" style="color: rgb(0,102); box-sizing: border-box;">0</span>;

    <span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">virtual</span> <span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">void</span> set32fPrecision(<span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">int</span> p = <span class="hljs-number" style="color: rgb(0,102); box-sizing: border-box;">8</span>) = <span class="hljs-number" style="color: rgb(0,102); box-sizing: border-box;">0</span>;
    <span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">void</span> set64fPrecision(<span class="hljs-keyword" style="color: rgb(0,102); box-sizing: border-box;">16</span>) = <span class="hljs-number" style="color: rgb(0,136); box-sizing: border-box;">void</span> setMultiline(<span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">bool</span> ml = <span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">true</span>) = <span class="hljs-number" style="color: rgb(0,136); box-sizing: border-box;">static</span> Ptr<Formatter> <span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">get</span>(<span class="hljs-keyword" style="color: rgb(0,136); box-sizing: border-box;">int</span> fmt = FMT_DEFAULT);

};
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238,221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul>
 
 
读取CSV数据
 
 
在保存为CSV格式后该如何读取呢，这里可以使用OpenCV中ml模块的TrainData类的函数读取。具体代码如下所示，第二行为加载数据，参数0表示没有标题行，第三行获取得到的数据。
 
 
 
 
代码运行结果为：
 
 
 
参考链接：
 1.OpenCV使用FileStorage保存Mat数据
 2.XML/YAML file storages. Writing to a file storage.