procedure TImageListItem.MyTest;
var LBmp  : TIEBitmap;
    LImgIO: TImageEnIO;
begin
  // Test file 1...
  TMemoryStream(ImgStream2).SaveToFile(OmTmpPath + 'Img.bmp');
  // Convert...
  LBmp   := TIEBitmap.Create;
  LImgIO := TImageEnIO.Create(nil);
  try
    ImgStream2.Position := 0;
    LImgIO.AttachedIEBitmap := LBmp;
    LImgIO.Params.TIFF_ImageIndex := 0;
    LImgIO.LoadFromStreamFormat(ImgStream2, IEExtToFileFormat('bmp'));
    LImgIO.Params.TIFF_Compression := ioTIFF_G4FAX;
    TMemoryStream(ImgStream2).Clear;
    LImgIO.AttachedIEBitmap := LBmp;
    LImgIO.SaveToStream(ImgStream2, IEExtToFileFormat('tif'));
    // Test file 2...
    TMemoryStream(ImgStream2).SaveToFile(OmTmpPath + 'Img.tif');
  finally
    LBmp.Free;
    LImgIO.Free;
  end;
end;

...
LImgIO.Params.TIFF_Compression := ioTIFF_G4FAX;
LImgIO.Params.BitsPerSample := 1;
LImgIO.Params.SamplesPerPixel := 1;
if LBmp.PixelFormat <> ie1g then
  LBmp.PixelFormat := ie1g;
...