两层image 叠加保存(10分)

我有两层image,上面一层是透明的，下面一层是图像，在上层画了一些图形，我想把这两层image按照当前的显示，保存到一个bitmap 钟，请问有什么好方法？

procedure DrawTransparent(var sBmp: TBitMap; dBmp: TBitMap; PosX, PosY: Integer; TranColor: TColor = -1);
type
PRGBTripleArray = ^TRGBTripleArray;
TRGBTripleArray = array[0..32767] of TRGBTriple;
function GetSLCOlor(pRGB: TRGBTriple): TColor;
begin
Result := RGB(pRGB.rgbtRed, pRGB.rgbtGreen, pRGB.rgbtBlue);
end;
var
b, p: PRGBTripleArray;
x, y: Integer;
BaseColor: TColor;
begin
sBmp.PixelFormat := pf24Bit;
dBmp.PixelFormat := pf24Bit;
p := dBmp.scanline[0];

if TranColor = -1 then
BaseCOlor := GetSLCOlor(p[0])
else
BaseCOlor := TranColor;

if (PosY > sBmp.Width) or (PosY > sBmp.Height) then
Exit;

for y := 0 to dBmp.Height - 1 do
begin
p := dBmp.scanline[y];
b := sBmp.ScanLine[y + PosY];
for x := 0 to (dBmp.Width - 1) do
begin
if GetSLCOlor(p[x]) <> BaseCOlor then
b[x + PosX] := p[x];
end;
end;

end;

procedure TForm1.Button1Click(Sender: TObject);
var
bmp:TBitMap;
begin
bmp:=TBitMap.Create ;
bmp.Assign(Image1.Picture);
DrawTransparent(bmp,Image2.Picture.Bitmap ,10,10);
image1.Picture.Assign(bmp);
image1.Refresh ;

end;

接受答案了.