求插值改变图形大小算法

Question

用了很多方法，在缩小图形时失真到了忍无可忍的地步，哪位大哥有好的插值算法给偶用用吧，不甚感激

Answer 1

with Self do  
begin
  setstretchbltmode(Canvas.Handle,HALFTONE);
  Canvas.CopyRect(DestRect,Image1.Canvas,SourceRect);
end;

Answer 2

使用方法：
BmpFile1 :要缩放的原始图文件名
BmpFile2 :缩放并存盘的文件名
w2: 缩放后的图像宽度
h2: 缩放后的图像高度procedure ResizeBMP(BmpFile1,BmpFile2:String;w2,h2:Integer);
{作用：将位图BmpFIle1调整大小为w,h并存盘于BmpFile2中}
var
 Bmp1,Bmp2 :TBitmap;
 w1,h1:Integer;
begin
  Bmp1 :=TBitmap.Create;
  Bmp2 :=TBitmap.Create;  Bmp1.LoadFromFile(BmpFile1);  w1:=Bmp1.Width;
  h1:=Bmp1.Height;
  
 Bmp2.Width :=w1*w2 div w1;
 Bmp2.Height :=h1*h2 div h1; SetStretchBltMode(Bmp2.Canvas.Handle,HalfTone);
 StretchBlt(Bmp2.Canvas.Handle,0,0,w2,h2,
            Bmp1.Canvas.Handle,0,0,w1,h1,SRCCOPY);
 Bmp2.SaveToFile(BmpFile2);
 Bmp1.Free;
 Bmp2.Free;
end;

Answer 3

function StretchBmp(SrcBmp:TBitmap;DesBmp:TBitmap;StretchRate:Integer):Boolean;
//stretch an bitmap to a smaller bmp, stretchRate is from 0 to 100.
//from tangfeng
//2003.01.19
var
  P1,P2:PByteArray;
  x1,y1,x2,y2,r,g,b:Integer;
begin
  Result:=false;
  if StretchRate>=100 then
    exit;
  try
    DesBmp.PixelFormat:=pf24Bit;
    DesBmp.Width:=SrcBmp.Width*StretchRate div 100;
    DesBmp.Height:=SrcBmp.Height*StretchRate div 100;
    for y1:=0 to DesBmp.Height-1 do begin
      y2:=y1*100 div StretchRate;         //¼ÆËã³öSourceͼÏóÖжÔÓ¦µÄÏóËصãY·½ÏòλÖõÄÖµ
      P1:=DesBmp.Scanline[y1];
      for x1:=0 to DesBmp.Width-1 do begin
        x2:=x1*100 div StretchRate;          //¼ÆËã³öSourceͼÏóÖжÔÓ¦µÄÏóËصãX·½ÏòλÖõÄÖµ
        P2:=SrcBmp.ScanLine[y2];
        if (x1=0) or (x1=DesBmp.Width-1) or (y1=0) or (y1=DesBmp.Height-1) then begin
          P1[x1*3]:=P2[x2*3];
          P1[x1*3+1]:=P2[x2*3+1];
          P1[x1*3+2]:=P2[x2*3+2];
          continue;
        end;
        r:=P2[(x2-SrcBmp.Width)*3]+P2[(x2-1)*3]+P2[(x2+SrcBmp.Width)*3]+P2[(x2+1)*3]+P2[x2*3];
        g:=P2[(x2-SrcBmp.Width)*3+1]+P2[(x2-1)*3+1]+P2[(x2+SrcBmp.Width)*3+1]+P2[(x2+1)*3+1]+P2[x2*3+1];
        b:=P2[(x2-SrcBmp.Width)*3+2]+P2[(x2-1)*3+2]+P2[(x2+SrcBmp.Width)*3+2]+P2[(x2+1)*3+2]+P2[x2*3+2];
        P1[x1*3]:=min(P2[x2*3],r div 5);
        P1[x1*3+1]:=min(P2[x2*3+1],g div 5);
        P1[x1*3+2]:=min(P2[x2*3+2],b div 5);
      end;
    end;
    Result:=true;
  except
  end;
end;

Answer 4

有没有JPG,GIF格式的算法呀？？做缩略图用的。谢谢。若好用，奉上200大洋。