Delphi DIB with DIB Header into TBitmap

Question

I'm kindly asking you to help me with this problem:

There's a byte array (data: PByte) containing DIB data AND DIBHeader:

  TDibHeader = record
    size: Cardinal;
    width: Integer;
    height: Integer;
    planes: Word;
    bits: Word;
    compression: Cardinal;
    image_size: Cardinal;
    x_res: Integer;
    y_res: Integer;
    n_colors: Cardinal;
    important_colors: Cardinal;
  end;

How to convert DIB to TBitmap while keeping the CPU usage low ?

I've tried http://files.codes-sources.com/fichier.aspx?id=43989&f=GdipApi.pas with no success.

I've assigned DIB to an Memory Stream:

  DibMemStream.Clear;
  DibMemStream.SetSize(header.image_size);
  MoveMemory(DibMemStream.Memory,DibBuffer,header.image_size);

I suppose there should be DIB header written somewhere before Bitmap.LoadFromMemoryStream(DibMemStream). Not sure where.

Any ideas please ?

Thank you !

Answer 1

I have used the following scheme to convert in-memory images to TBitmap:

1) Fill TBMPHeader structure

  TBMPHeader = packed record
    bmfHeader: TBitmapFileHeader;
    bmiHeader: TBitmapInfoHeader;
    bmiColors: {depends on image format, may be absent};
  end;

2) Write BMPHeader + Image Data to MemoryStream

3) Load TBitmap from MemoryStream using TBitmap.LoadFromStream

You seems to have bmiHeader structure filled already. Add bmfHeader and (maybe) bmiColors.

Here is the code I used to convert 256-color grayscale in-memory images to TBitmap (many years ago, sorry, so no details):

procedure TksImage.CopyToBitmap(Bitmap: TBitmap);
var
  Stream: TStream;

begin
  Stream:= TMemoryStream.Create;
  try
    SaveToStream(Stream);
    Stream.Position:= 0;
    Bitmap.LoadFromStream(Stream);
  finally
    Stream.Free;
  end;
end;

procedure TksImage.SaveToStream(Stream: TStream);
type
  TBMPHeader = packed record
    bmfHeader: TBitmapFileHeader;
    bmiHeader: TBitmapInfoHeader;
    bmiColors: array[0..255] of TRGBQuad;
  end;

var
  BMPHeader: TBMPHeader;
  N: LongWord;
  I: Integer;

begin
  FillChar(BMPHeader, SizeOf(BMPHeader), 0);
  with BMPHeader.bmfHeader do begin
    bfType:= $4D42; {'BM'}
    bfOffBits:= SizeOf(BMPHeader);
    if FChannels = 4 then Dec(bfOffBits, SizeOf(BMPHeader.bmiColors));
    bfSize:= bfOffBits + LongWord(FImageSize);
  end;
  with BMPHeader.bmiHeader do begin
    biSize:= SizeOf(BMPHeader.bmiHeader);
    biWidth:= FWidth;
    biHeight:= FHeight;
    biPlanes:= 1;
    biBitCount:= 8 * FChannels;
    biCompression:= BI_RGB;
    biSizeImage:= FImageSize;
    {((((biWidth * biBitCount) + 31) and not 31) shr 3) * biHeight;}
  end;
  N:= 0;
  for I:= 0 to 255 do begin
    LongWord(bmpHeader.bmiColors[I]):= N;
    Inc(N, $010101);
  end;
  Stream.Write(BMPHeader, BMPHeader.bmfHeader.bfOffBits);
  Stream.Write(FImageData^, FImageSize);
end;