Save a TJEPGImage with DPI information

Problem/Question/Abstract:

I need to save a JPEG with DPI information, but cannot find a PPI or DPI property to set. I know that .JPG headers include horizontal and vertical DPI information, but cannot find a correponding property in Delphi 6's TJPEGImage object. Does anyone know how to do this?

Answer:

procedure SetJpgdpi(filename: string; dpix, dpiy: Integer);
const
  BufferSize = 50;
  DPI = 1; {inch}
  DPC = 2; {cm}
var
  Buffer: string;
  index: Integer;
  FileStream: TFileStream;
  xResolution: WORD;
  yResolution: WORD;
type
  : Byte;
begin
  FileStream := TFileStream.Create(filename, fmOpenReadWrite);
  try
    SetLength(Buffer, BufferSize);
    FileStream.Read(buffer[1], BufferSize);
    index := Pos('JFIF' + #$00, buffer);
    if index > 0 then
    begin
      FileStream.Seek(index + 6, soFromBeginning);
    type
      := DPI;
      FileStream.write(type, 1);
      xresolution := swap(dpix);
      FileStream.write(xresolution, 2);
      yresolution := swap(dpiy);
      FileStream.write(yresolution, 2);
    end
  finally
    FileStream.Free;
  end;
end;