如何将存储在 MySQL 表中的位图图像转换为 JPEG 格式？

Question

我有一个存储位图图像的 MySQL 表，我想将它们转换为 JPEG 格式到同一个表。谁能帮我找到解决方案？

我需要这个来减小表格的大小...

Answer 1

当您使用 ADO 访问您的 MySQL 数据库时，它可能看起来像这样（未经测试）。此代码假定您拥有要使用的名为 YourTable 的表和要转换图像的 BLOB 字段为 ImageField。请注意，您必须在 ADOConnection 对象的 ConnectionString 属性中指定与数据库的连接字符串：

uses
  DB, ADODB, JPEG;

procedure ConvertImage(BlobField: TBlobField);
var
  BMPImage: TBitmap;
  JPEGImage: TJPEGImage;
  MemoryStream: TMemoryStream;
begin
  MemoryStream := TMemoryStream.Create;
  try
    BlobField.SaveToStream(MemoryStream);
    BMPImage := TBitmap.Create;
    try
      MemoryStream.Position := 0;
      BMPImage.LoadFromStream(MemoryStream);
      JPEGImage := TJPEGImage.Create;
      try
        JPEGImage.Assign(BMPImage);
        MemoryStream.Position := 0;
        JPEGImage.SaveToStream(MemoryStream);
      finally
        JPEGImage.Free;
      end;
    finally
      BMPImage.Free;
    end;
    MemoryStream.Position := 0;
    BlobField.LoadFromStream(MemoryStream);
  finally
    MemoryStream.Free;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  ADOTable: TADOTable;
  ADOConnection: TADOConnection;
begin
  ADOConnection := TADOConnection.Create(nil);
  try
    ADOConnection.LoginPrompt := False;
    // here you have to specify the connection string to your database
    // according to your connection parameters
    ADOConnection.ConnectionString := '<enter your connection string here>';
    ADOConnection.Open;
    if ADOConnection.Connected then
    begin
      ADOTable := TADOTable.Create(nil);
      try
        ADOTable.Connection := ADOConnection;
        ADOTable.TableName := 'YourTable';
        ADOTable.Filter := 'ImageField IS NOT NULL';
        ADOTable.Filtered := True;
        ADOTable.CursorType := ctOpenForwardOnly;
        ADOTable.Open;
        ADOTable.First;
        while not ADOTable.Eof do
        begin
          ADOTable.Edit;
          ConvertImage(TBlobField(ADOTable.FieldByName('ImageField')));
          ADOTable.Post;
          ADOTable.Next;
        end;
      finally
        ADOTable.Free;
      end;
    end;
  finally
    ADOConnection.Free;
  end;
end;