Canvas好像没有提供这些方法.(没找到)
不过可以用Image控件的Canvas画图.
然后image1.Picture.SaveToFile试试看

procedure TForm1.SavePicClick(Sender: TObject);
var
  i:Integer;
  str:string;
begin
  for i:=1 to 100  do
  begin
  if FileExists(str) then  else
      begin
       str:='D:\Borland\Delphi7\Projects\mychart\pic'+inttostr(i)+'.bmp';
       Image1.Picture.SaveToFile(str);
       str:='D:\Borland\Delphi7\Projects\mychart\pic'+inttostr(i+1)+'.bmp';
       Image2.Picture.SaveToFile(str);
       exit;
      end;
  end;end;

提供一个这样的函数给你参考：procedure TFrmDesktop.FixSize(const vFileName: String);
var
  vBitmap3: TBitmap;
  vImage: TImage;
//  DC2, vDC: HDC;
begin
  try
    vImage := TImage.Create(self);
    vImage.Visible := False;
    vImage.AutoSize := true;
    vBitmap3 := TBitmap.Create;
//    vBitmap3.Width := 800;
//    vBitmap3.Height := 600;
    if CompareText(vExt, 'Bmp') = 0 then vImage.Picture.LoadFromFile(OpenDialog1.FileName);
    if CompareText(vExt, 'Jpg') = 0 then vImage.Picture.LoadFromFile(vFileName);
    if vImage.Picture.Bitmap.Height / vImage.Picture.Bitmap.Width > 0.75 then
    begin
      if vImage.Picture.Bitmap.Height >= ScreenY then
      begin
        vImage.Canvas.StretchDraw(Rect(0,0,round(vImage.Picture.Bitmap.Width * ScreenY/vImage.Picture.Bitmap.Height),ScreenY),vImage.Picture.Bitmap);
        vImage.Center := True;
        vBitmap3.Width := round(vImage.Picture.Bitmap.Width * ScreenY/vImage.Picture.Bitmap.Height);
        vBitmap3.Height := ScreenY;
  //    StretchBlt(vDC, 0, 0, 800, 600, DC2, Image2.Left, Image2.Top, Image2.Width, Image2.Height, SRCCOPY);
    //  vImage.Canvas.CopyRect(Rect(0,0, vImage.Width,vImage.Height), Image2.Canvas, Rect(0,0,Image2.Width,Image2.Height));
        vBitmap3.Canvas.CopyRect(Rect(0,0,vBitmap3.Width,vBitmap3.Height), vImage.Canvas, Rect(0,0,round(vImage.Picture.Bitmap.Width * ScreenY/vImage.Picture.Bitmap.Height),ScreenY));
  //    vImage.Picture.SaveToFile('E:\My Documents\My Pictures\Wally.bmp');
//    vBitmap3.Canvas.CopyRect(Rect(0,0,vBitmap3.Width,vBitmap3.Height), Image2.Canvas, Rect(0,0,Image2.Width,Image2.Height));
    //    if StretchBlt(vDC, 0, 0, 800, 600, DC2, Image2.Left, Image2.Top, Image2.Width, Image2.Height, SRCCOPY) then
//    BitBlt(vDC, 0, 0, 800, 600, DC2, Image2.Width, Image2.Height, SRCCOPY);
//    Image2.Picture.Graphic.SaveToFile('E:\My Documents\My Pictures\Wally.bmp');
        vBitmap3.SaveToFile(vFileName);
      end
      else
        vImage.Picture.Bitmap.SaveToFile(vFileName);
    end
    else if vImage.Picture.Bitmap.Height / vImage.Picture.Bitmap.Width < 0.75 then
    begin
      if vImage.Picture.Bitmap.Width >= ScreenX then
      begin
        vImage.Canvas.StretchDraw(Rect(0,0,ScreenX,round(vImage.Picture.Bitmap.Height * ScreenX/vImage.Picture.Bitmap.Width)),vImage.Picture.Bitmap);
        vImage.Center := True;
        vBitmap3.Height := round(vImage.Picture.Bitmap.Height * ScreenX/vImage.Picture.Bitmap.Width);
        vBitmap3.Width := ScreenX;
        vBitmap3.Canvas.CopyRect(Rect(0,0,vBitmap3.Width,vBitmap3.Height), vImage.Canvas, Rect(0, 0, ScreenX, round(vImage.Picture.Bitmap.Height * ScreenX/vImage.Picture.Bitmap.Width)));
        vBitmap3.SaveToFile(vFileName);
      end
      else
        vImage.Picture.Bitmap.SaveToFile(vFileName);
    end
    else
    begin
      if vImage.Picture.Bitmap.Height >= ScreenY then
      begin
        vImage.Canvas.StretchDraw(Rect(0,0,ScreenX,ScreenY),vImage.Picture.Bitmap);
        vImage.Center := True;
        vBitmap3.Width := ScreenX;
        vBitmap3.Height := ScreenY;
        vBitmap3.Canvas.CopyRect(Rect(0,0,vBitmap3.Width,vBitmap3.Height), vImage.Canvas, Rect(0,0,ScreenX,ScreenY));
        vBitmap3.SaveToFile(vFileName);
      end
      else
        vImage.Picture.Bitmap.SaveToFile(vFileName);
    end;
  finally
    vImage.free;
  end;
end;