Конвертер png -> jpeg

// сохраняю
procedure TForm1.Button1Click(Sender: TObject);
begin
  if SavePictureDialog1.Execute then
    if FileExists(SavePictureDialog1.FileName) then
        raise Exception.Create('File already exists. Cannot overwrite.')
    else
      Image1.Picture.SaveToFile(SavePictureDialog1.FileName);
end;
 
// загружаю
procedure TForm1.sbFromClick(Sender: TObject);
begin
  if OpenPictureDialog1.Execute then
    Image1.Picture.LoadFromFile(OpenPictureDialog1.FileName);
end;

procedure PNGFileToBitmap(const Source, Dest: String);
var
  Jpg: TJpegImage;
  PNG: TPNGObject;
begin
  PNG := TPNGObject.Create;
  Jpg := TJpegImage.Create;
  {In case something goes wrong, free booth PNG and Bitmap}
  try
    PNG.LoadFromFile(Source);
    Jpg.Assign(PNG);    //Convert data into bitmap
    Jpg.SaveToFile(Dest);
  finally
    PNG.Free;
    Jpg.Free;
  end
end;

procedure PNGtoJPEG(const Source, Dest: String;  Quality: TJPEGQualityRange=100);
var
  Bitmap: TBitmap;
  PNG: TPNGObject;
  Jpg: TJpegImage;
begin
  PNG := TPNGObject.Create;
  Bitmap := TBitmap.Create;
  try
    PNG.LoadFromFile(Source);
    Bitmap.Assign(PNG); 
    Jpg := TJpegImage.Create;
    Jpg.CompressionQuality:=Quality;
    Jpg.Assign(Bitmap);
    Jpg.SaveToFile(ChangeFileExt(Dest, '.jpg' ));
  finally
    jpg.free;
    PNG.Free;
    Bitmap.Free;
  end
end;

function KindOfImage(Start: Pointer): String;
var
  PW: ^Word absolute Start;
  PL: ^DWord absolute Start;
begin
  result := 'UnKnow';
  if PL^ = $474E5089 then Result := 'PNG';
  if PW^ = $D8FF then Result := 'JPG'
end;

function KindOfImage(const Start: Pointer): string;
begin
  if PCardinal(Start)^ = $474E5089 then 
    Result := 'PNG'
  else if PCardinal(Start)^ and $00FFFFFF = $00FFD8FF then 
    Result := 'JPG'
  else
    Result := 'Unknown';
end;

type
  TImageType = (NoImage, Bmp, Gif, Gif89, Png, Jpg);
 
function KindOfImage(Start: Pointer): TImageType;
begin
  if LongWord(Start^) = $38464947 then
  begin
    if (PChar(Start) + 4)^ = '9' then Result := Gif89
    else Result := Gif;
  end
  else if Word(Start^) = $4D42 then Result := Bmp
  else if LongWord(Start^) = $474E5089 then Result := Png
  else if Word(Start^) = $D8FF then Result := Jpg
  else Result := NoImage;
end;

var
  img : TMemoryStream;
begin
  img := TMemoryStream.Create;
  img.LoadFromFile(fileName);
  case  KindOfImage(img.Memory) of
  0  :
  1  :
  2  :
  end;
end;