图片分辨率的调整：
procedure TForm1.Button1Click(Sender: TObject);
var
 abmp,bbmp:tbitmap;
 scale:real;
 p:tpoint;
begin
 abmp:=tbitmap.Create;
 bbmp:=tbitmap.Create;
 p.x:=10;
 p.y:=10;
 if open.Execute then
 begin
 abmp.LoadFromFile(open.FileName);
 scale:=abmp.Width/800;
 bbmp.Width:=round(abmp.Width/scale);
 bbmp.Height:=round(abmp.Height/scale);
 bbmp.PixelFormat:=abmp.PixelFormat;
 SetStretchBltMode(bbmp.Canvas.Handle,COLORONCOLOR);
//if SetBrushOrgEx(bbmp.Canvas.Handle,0,0,@p) then
  begin
  stretchblt(bbmp.Canvas.Handle,0,0,bbmp.Width,bbmp.Height,abmp.Canvas.Handle,0,0,abmp.Width,abmp.Height,srccopy);
  bbmp.SaveToFile('c:\windows\desktop\aaa.bmp');
  end;
 end;
 abmp.Free;
 bbmp.Free;
end;