if(n_RowWidth%8 == 0)

                n_RowByte = n_RowWidth/2;

            else

                n_RowByte = (n_RowWidth/8+1)*4;

            break;

        // 8位索引图

        case 8:

            if(n_RowWidth%4 == 0)

                n_RowByte = n_RowWidth;

            else

                n_RowByte = (n_RowWidth/4+1)*4;

            break;

        // 真彩图

        case 24:

            if((n_RowWidth*3)%4 == 0)

                n_RowByte = n_RowWidth*3;

            else

                n_RowByte = (n_RowWidth*3/4+1)*4;

            break;

        default:

            AfxMessageBox("Have not set such bmp format");

            return -1;

    }

    return n_RowByte;

}

该函数根据图像宽度，返回一行图像所占的字节数。biBitCount：同BitmapInfoHeader中的biBitCount，n_RowWidth：图像中每行的像素数。该函数的关键是保证每行像素占用的字节数是4的倍数。