Sharpen a Bitmap

Материал из DRKB


Добавление резкости это смешивание текущего пикселя со средним значением окружающих пикселей, но с отрицательным влиянием на среднее значение.

// to sharpen, alpha must be >1.
// pixelformat pf24bit
// sharpens sbm to tbm
procedure Sharpen(sbm, tbm: TBitmap; alpha: Single);
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
      // calculate 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;


Source: http://www.swissdelphicenter.ch/en/tipsindex.php
ID: 03863