title: In the .bmp file structure on windows, why is "biSizeImage" not equal to "width * height * (biBitCount / 8)"?
body: <p>I wrote a program to read the .bmp file. Here is the information of this the .bmp file:</p>
  
  <p><a href="https://i.stack.imgur.com/KS4oe.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/KS4oe.png" alt="running result"></a></p>
  
  <p>here is another test image：</p>
  
  <p><a href="https://i.stack.imgur.com/X4yiR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/X4yiR.png" alt="another test"></a></p>
  
  <p>I found the "biSizeImage" not equal to "width * height * (biBitCount / 8)", why does that happen?</p>