title: explorer get image's thumbnail really fast, how does it work?
body: <p>I am using explorer to view image in thumbnail mode.
  It is really fast to get thumbnail of each image(bmp, jpg).</p>
  
  <p>I am using the following code to generate thumbnails for each image. however it is much slower than the explorer, How can I write a part of code to generate thumbnail as fast as system and accurate(thumbnail generated by the following code sometimes have black band on top and bottom, or on left and right side, I don't know why...). Or can I envoke explorer's API to generate thumbnail using its function?</p>
  
  <pre><code>Bitmap sourceImg(xxx);
  int nSize = sourceImg.GetPropertyItemSize(PropertyTagThumbnailData);
  if(nSize &gt; 0)
      {
      PropertyItem * pItem = (PropertyItem*)malloc(nSize);
      if (pItem != NULL)
      {
          sourceImg.GetPropertyItem(PropertyTagThumbnailData, nSize, pItem);
      }
      GenerateThumbnail from pItem.....
  }
  </code></pre>