How to get dimensions of image file in Delphi?

Question

I want to know width and height of an image file before opening that file.

So, how to do that?

EDIT: This refers to jpg, bmp, png and gif types of image fil

Answer 1

I don't like Rafael's solution for JPGs too much because his algorithm parses every single byte until it hits FFC0. It doesn't make use of the fact that almost all markers (except FFD8,FFD9 and FFFE) are followed by two length bytes, allowing to skip from marker to marker. So I suggest the following procedure (which I condensed even a little more by stuffing checking for a marker and retrieving a value into the same function):

procedure GetJPGSize(const Filename: string; var ImgWidth, ImgHeight: word);
const
  SigJPG : TBytes = [$FF, $D8];
  SigC01 : TBytes = [$FF, $C0];
  SigC02 : TBytes = [$FF, $C1];
var
  FStream: TFileStream;
  Buf: array[0..1] of Byte;
  Offset,CheckMarker : Word;
//--------------------------------------------------------------------------------------------------------------------------------------------------------------
  function  SameValue(Sig:TBytes):Boolean;
  begin
     Result := CompareMem(@Sig[0], @Buf[0], Length(Sig));
  end;
//--------------------------------------------------------------------------------------------------------------------------------------------------------------
  function  CheckMarkerOrVal(var Value:Word):Boolean;
  begin
    FStream.ReadData(Buf, Length(Buf));
    Value := Swap(PWord(@Buf[0])^);
    Result := (Buf[0] = $FF);
  end;
//--------------------------------------------------------------------------------------------------------------------------------------------------------------
begin
  FStream := TFileStream.Create(Filename, fmOpenRead);
  Try
    // First two bytes in a JPG file MUST be $FFD8, followed by the next marker
    If not (CheckMarkerOrVal(CheckMarker) and SameValue(SigJPG))
      then exit;
    Repeat
      If not CheckMarkerOrVal(CheckMarker)
        then exit;
      If SameValue(SigC01) or SameValue(SigC02) then begin
        FStream.Position := FStream.Position + 3;
        CheckMarkerOrVal(ImgHeight);
        CheckMarkerOrVal(ImgWidth);
        exit;
      end;
      CheckMarkerOrVal(Offset);
      FStream.Position := FStream.Position + Offset - 2;
    until FStream.Position > FStream.Size div 2;
  Finally
    FStream.Free;
  end;
end;