procedure MakeThumbNail(const Src, Dest: TBitmap);
type
 PRGB24 = ^TRGB24;
 TRGB24 = packed record
  B: Byte;
  G: Byte;
  R: Byte;
 end;
var
 x, y, ix, iy: integer;
 x1, x2, x3: integer;
 xscale, yscale: single;
 iRed, iGrn, iBlu, iRatio: Longword;
 p, c1, c2, c3, c4, c5: tRGB24;
 pt, pt1: pRGB24;
 iSrc, iDst, s1: integer;
 i, j, r, g, b, tmpY: integer;
 RowDest, RowSource, RowSourceStart: integer;
 w, h: integer;
 dxmin, dymin: integer;
 ny1, ny2, ny3: integer;
 dx, dy: integer;
 lutX, lutY: array of integer;
begin
 if src.PixelFormat <> pf24bit then src.PixelFormat := pf24bit;
 if dest.PixelFormat <> pf24bit then dest.PixelFormat := pf24bit;
 w := Dest.Width;
 h := Dest.Height;
 if (src.Width <= dest.Width) and (src.Height <= dest.Height) then
 begin
  dest.Assign(src);
  exit;
 end;
 iDst := (w * 24 + 31) and not 31;
 iDst := iDst div 8; //BytesPerScanline
 iSrc := (Src.Width * 24 + 31) and not 31;
 iSrc := iSrc div 8;
 xscale := 1 / (w / src.Width);
 yscale := 1 / (h / src.Height);
 // X lookup table
 SetLength(lutX, w);
 x1 := 0;
 x2 := trunc(xscale);
 for x := 0 to w - 1 do
 begin
  lutX[x] := x2 - x1;
  x1 := x2;
  x2 := trunc((x + 2) * xscale);
 end;
 // Y lookup table
 SetLength(lutY, h);
 x1 := 0;
 x2 := trunc(yscale);
 for x := 0 to h - 1 do
 begin
  lutY[x] := x2 - x1;
  x1 := x2;
  x2 := trunc((x + 2) * yscale);
 end;
 dec(w);
 dec(h);
 RowDest := integer(Dest.Scanline[0]);
 RowSourceStart := integer(Src.Scanline[0]);
 RowSource := RowSourceStart;
 for y := 0 to h do
 begin
  dy := lutY[y];
  x1 := 0;
  x3 := 0;
  for x := 0 to w do
  begin
  dx:= lutX[x];
  iRed:= 0;
  iGrn:= 0;
  iBlu:= 0;
  RowSource := RowSourceStart;
  for iy := 1 to dy do
  begin
  pt := PRGB24(RowSource + x1);
  for ix := 1 to dx do
  begin
  iRed := iRed + pt.R;
  iGrn := iGrn + pt.G;
  iBlu := iBlu + pt.B;
  inc(pt);
  end;
  RowSource := RowSource - iSrc;
  end;
  iRatio := 65535 div (dx * dy);
  pt1 := PRGB24(RowDest + x3);
  pt1.R := (iRed * iRatio) shr 16;
  pt1.G := (iGrn * iRatio) shr 16;
  pt1.B := (iBlu * iRatio) shr 16;
  x1 := x1 + 3 * dx;
  inc(x3,3);
  end;
  RowDest := RowDest - iDst;
  RowSourceStart := RowSource;
 end;
 if dest.Height < 3 then exit;
 // Sharpening...
 s1 := integer(dest.ScanLine[0]);
 iDst := integer(dest.ScanLine[1]) - s1;
 ny1 := Integer(s1);
 ny2 := ny1 + iDst;
 ny3 := ny2 + iDst;
 for y := 1 to dest.Height - 2 do
 begin
  for x := 0 to dest.Width - 3 do
  begin
  x1 := x * 3;
  x2 := x1 + 3;
  x3 := x1 + 6;
  c1 := pRGB24(ny1 + x1)^;
  c2 := pRGB24(ny1 + x3)^;
  c3 := pRGB24(ny2 + x2)^;
  c4 := pRGB24(ny3 + x1)^;
  c5 := pRGB24(ny3 + x3)^;
  r := (c1.R + c2.R + (c3.R * -12) + c4.R + c5.R) div -8;
  g := (c1.G + c2.G + (c3.G * -12) + c4.G + c5.G) div -8;
  b := (c1.B + c2.B + (c3.B * -12) + c4.B + c5.B) div -8;
  if r < 0 then r := 0 else if r > 255 then r := 255;
  if g < 0 then g := 0 else if g > 255 then g := 255;
  if b < 0 then b := 0 else if b > 255 then b := 255;
  pt1 := pRGB24(ny2 + x2);
  pt1.R := r;
  pt1.G := g;
  pt1.B := b;
  end;
  inc(ny1, iDst);
  inc(ny2, iDst);
  inc(ny3, iDst);
 end;
end;

SetStretchBltMode(Canvas.Handle, HALFTONE);