在image控件中如何使显示的图象按象素缩小？

DbImage1就是IMAGE，我起的一个名字而已var  DrawRect:TRect;
     ClearBitMap:TBitMap;
begin
  DbImage1.Visible:=true;
  ScrollBox1.HorzScrollBar.Range:=Round(0.8*DBimage1.Width);   //按比率缩小
  ScrollBox1.VertScrollBar.Range:=Round(0.8*DBimage1.Height);
  DBimage1.Left:=0;
  DBimage1.Top:=0;
  DBimage1.Width:=ScrollBox1.HorzScrollBar.Range;
  DBimage1.Height:=ScrollBox1.VertScrollBar.Range;
  DBimage1.Picture.Bitmap.Width:=DBimage1.Width;
  DBimage1.Picture.Bitmap.Height:=DBimage1.Height;  DrawRect.Top:=0;
  DrawRect.Left:=0;
  DrawRect.Right:=DBImage1.Width;
  DrawRect.Bottom:=DBImage1.Height;
  ClearBitmap:=TBitmap.Create;
  ClearBitmap.Width:=DBImage1.Width;
  ClearBitmap.Height:=DBImage1.Height;
  DBImage1.Picture.Bitmap.Canvas.Draw(0,0,ClearBitmap); //清空
  ClearBitmap.Free;
  DBImage1.Picture.Bitmap.Canvas.StretchDraw(DrawRect,image5.picture.Graphic);//重画
  DBimage1.Refresh;
  if (DBimage1.Width<ScrollBox1.Width) then DBimage1.Left:=(ScrollBox1.Width div 2 - dbimage1.Width div 2);//置中
  if (DBimage1.Height<ScrollBox1.Height) then DBimage1.Top:=(ScrollBox1.Height div 2 - dbimage1.Height div 2);