Максимально эффективно нарисовать точку на форме

type
  TColor2Grayscale = (
    c2gAverage,
    c2gLightness,
    c2gLuminosity
  );
 
  TBitmapAccess = (
    baScanLine,
    baPixels
  );
 
// ...
 
function RGBToGray(R, G, B: byte; cg: TColor2Grayscale = c2gLuminosity): byte;
begin
  case cg of
    c2gAverage:
      Result := (R + G + B) div 3;
 
    c2gLightness:
      Result := (max(R, G, B) + min(R, G, B)) div 2;
 
    c2gLuminosity:
      Result := round(0.2989*R + 0.5870*G + 0.1141*B); // coeffs from Matlab
 
    else
      raise Exception.Create('Unknown Color2Grayscale value');
  end;
end;
 
// ...
 
procedure ToGray(aBitmap: Graphics.TBitmap;
  cg: TColor2Grayscale = c2gLuminosity;
  ba: TBitmapAccess = baScanLine);
var w, h: integer; CurrRow, OffSet: integer;
  x: byte; pRed, pGreen, pBlue: PByte;
begin
  if ba = baPixels then
  begin
    if aBitmap <> nil then
      for h := 0 to aBitmap.Height - 1 do
        for w := 0 to aBitmap.Width - 1 do
          aBitmap.Canvas.Pixels[w,h] :=
            ColorToGray(aBitmap.Canvas.Pixels[w,h], cg);
  end
 
  else // ba = baScanLine
  begin
    if aBitmap.PixelFormat <> pf24bit then
      raise Exception.Create(
        'Not implemented. PixelFormat has to be "pf24bit"');
 
    CurrRow := Integer(aBitmap.ScanLine[0]);
    OffSet := Integer(aBitmap.ScanLine[1]) - CurrRow;
 
    for h := 0 to aBitmap.Height - 1 do
    begin
      for w := 0 to aBitmap.Width - 1 do
      begin
        pBlue  := pByte(CurrRow + w*3);
        pGreen := pByte(CurrRow + w*3 + 1);
        pRed   := pByte(CurrRow + w*3 + 2);
        x := RGBToGray(pRed^, pGreen^, pBlue^, cg);
        pBlue^  := x;
        pGreen^ := x;
        pRed^   := x;
      end;
      inc(CurrRow, OffSet);
    end;
  end
end;

function TCanvas.GetPixel(X, Y: Integer): TColor;
begin
  RequiredState([csHandleValid]);
  GetPixel := Windows.GetPixel(FHandle, X, Y);  // тут тоже не быстрая WinApi -ф-ция
end;

function TBitmap.GetScanLine(Row: Integer): Pointer;
begin
  Changing(Self);
  with FImage.FDIB, dsbm, dsbmih do
  begin
    if (Row < 0) or (Row >= bmHeight) then
      InvalidOperation(@SScanLine);
    DIBNeeded;
    GDIFlush;
    if biHeight > 0 then  // bottom-up DIB
      Row := biHeight - Row - 1;
    Integer(Result) := Integer(bmBits) +
      Row * BytesPerScanline(biWidth, biBitCount, 32);
  end;
end;