title: bitmap.save changes its pixelFormat to 32-bit depth
body: <p>I'm facing an issue which I can't resolve somehow, so I decided to ask you guys.</p>
  
  <p>I have really simple code:</p>
  
  <pre><code>public void OpenSaveImageDialog(Bitmap bitmapImage)
      {
          var dlg = new SaveFileDialog
          {
              DefaultExt = DialogType.Image.defaultExt,
              Filter = DialogType.Image.filter
          };
  
          dlg.ShowDialog();
  
          bitmapImage.Save(dlg.FileName);
      }
  </code></pre>
  
  <p>Funcion parameters is a Bitmap with pixelFormat equal to 24bppRgb. It is really essential for me to preseve pixelFormat and bit depth during the save operation. But after I save the file and check its properties it's saved as 32 bit depth image. Why is that? How to fix this? </p>
  
  <p>Thanks. </p>