Store the resulting value in one extra byte at the end of the file. 将得到的值存储到文件尾部的一个额外字节中。
Since a32-bit DWORD has4 bytes, that leaves one extra byte by my count ( 4-3= 1). The extra byte is often used as the "alpha channel," used to specify the pixel's transparency. 由于32位的DWORD有4个字节,多余的这个字节常被用作“alphachannel”,用于指定像素的透明度。