Transform a TImage.Picture.Bitmap to GrayScale

Problem/Question/Abstract:

A TBitmap object has no method to convert to GrayScale mode.

Answer:

However, you can transform a Bitmap to GrayScale with the following procedure:

procedure ImageGrayScale(var AnImage: TImage);
var
  JPGImage: TJPEGImage;
  BMPImage: TBitmap;
  MemStream: TMemoryStream;
begin
  BMPImage := TBitmap.Create;
  try
    BMPImage.Width := AnImage.Picture.Bitmap.Width;
    BMPImage.Height := AnImage.Picture.Bitmap.Height;

    JPGImage := TJPEGImage.Create;
    try
      JPGImage.Assign(AnImage.Picture.Bitmap);
      JPGImage.CompressionQuality := 100;
      JPGImage.Compress;
      JPGImage.Grayscale := True;

      BMPImage.Canvas.Draw(0, 0, JPGImage);

      MemStream := TMemoryStream.Create;
      try
        BMPImage.SaveToStream(MemStream);
        //you need to reset the position of the MemoryStream to 0
        MemStream.Position := 0;

        AnImage.Picture.Bitmap.LoadFromStream(MemStream);
        AnImage.Refresh;
      finally
        MemStream.Free;
      end;
    finally
      JPGImage.Free;
    end;
  finally
    BMPImage.Free;
  end;
end; //fin de ImageGrayScale

The trick is to assign the content of the Bitmap to a JPEGImage, which has a GrayScale property, and then copy the content of the JPEGImage back to Bitmap, using a MemoryStream.

The only drawback is using a JPEGImage, because the JPEGImage has a lousy compression of the image, in other words you loose information with the compression, but the human eye doesn�t notice. If you kwnow another implementation please send me an e-mail.