procedure Sharpen(sbm, tbm: TBitmap; alpha: Single);
//to sharpen, alpha must be >1.
//pixelformat pf24bit
//sharpens sbm to tbm
var
 i, j, k: integer;
 sr: array[0..2] of PByte;
 st: array[0..4] of pRGBTriple;
 tr: PByte;
 tt, p: pRGBTriple;
 beta: Single;
 inta, intb: integer;
 bmh, bmw: integer;
 re, gr, bl: integer;
 BytesPerScanline: integer;
begin
 //sharpening is blending of the current pixel
 //with the average of the surrounding ones,
 //but with a negative weight for the average
 Assert((sbm.Width > 2) and (sbm.Height > 2), 'Bitmap must be at least 3x3');
 Assert((alpha > 1) and (alpha < 6), 'Alpha must be >1 and <6');
 beta := (alpha - 1) / 5; //we assume alpha>1 and beta<1
 intb := round(beta * $10000);
 inta := round(alpha * $10000); //integer scaled alpha and beta
 sbm.PixelFormat := pf24bit;
 tbm.PixelFormat := pf24bit;
 tbm.Width := sbm.Width;
 tbm.Height := sbm.Height;
 bmw := sbm.Width - 2;
 bmh := sbm.Height - 2;
 BytesPerScanline := (((bmw + 2) * 24 + 31) and not 31) div 8;
 tr := tbm.Scanline[0];
 tt := pRGBTriple(tr);
 sr[0] := sbm.Scanline[0];
 st[0] := pRGBTriple(sr[0]);
 for j := 0 to bmw + 1 do
 begin
  tt^ := st[0]^;
  inc(tt); inc(st[0]); //first row unchanged
 end;
 sr[1] := PByte(integer(sr[0]) - BytesPerScanline);
 sr[2] := PByte(integer(sr[1]) - BytesPerScanline);
 for i := 1 to bmh do
 begin
  Dec(tr, BytesPerScanline);
  tt := pRGBTriple(tr);
  st[0] := pRGBTriple(integer(sr[0]) + 3); //top
  st[1] := pRGBTriple(sr[1]); //left
  st[2] := pRGBTriple(integer(sr[1]) + 3); //center
  st[3] := pRGBTriple(integer(sr[1]) + 6); //right
  st[4] := pRGBTriple(integer(sr[2]) + 3); //bottom
  tt^ := st[1]^; //1st col unchanged
  for j := 1 to bmw do
  begin
  //calcutate average weighted by -beta
  re := 0; gr := 0; bl := 0;
  for k := 0 to 4 do
  begin
  re := re + st[k]^.rgbtRed;
  gr := gr + st[k]^.rgbtGreen;
  bl := bl + st[k]^.rgbtBlue;
  inc(st[k]);
  end;
  re := (intb * re + $7FFF) shr 16;
  gr := (intb * gr + $7FFF) shr 16;
  bl := (intb * bl + $7FFF) shr 16;
  //add center pixel weighted by alpha
  p := pRGBTriple(st[1]); //after inc, st[1] is at center
  re := (inta * p^.rgbtRed + $7FFF) shr 16 - re;
  gr := (inta * p^.rgbtGreen + $7FFF) shr 16 - gr;
  bl := (inta * p^.rgbtBlue + $7FFF) shr 16 - bl;
  //clamp and move into target pixel
  inc(tt);
  if re < 0 then
  re := 0
  else
  if re > 255 then
  re := 255;
  if gr < 0 then
  gr := 0
  else
  if gr > 255 then
  gr := 255;
  if bl < 0 then
  bl := 0
  else
  if bl > 255 then
  bl := 255;
  //this looks stupid, but avoids function calls
  tt^.rgbtRed := re;
  tt^.rgbtGreen := gr;
  tt^.rgbtBlue := bl;
  end;
  inc(tt);
  inc(st[1]);
  tt^ := st[1]^; //Last col unchanged
  sr[0] := sr[1];
  sr[1] := sr[2];
  Dec(sr[2], BytesPerScanline);
 end;
 // copy last row
 Dec(tr, BytesPerScanline);
 tt := pRGBTriple(tr);
 st[1] := pRGBTriple(sr[1]);
 for j := 0 to bmw + 1 do
 begin
  tt^ := st[1]^;
  inc(tt); inc(st[1]);
 end;
end;