Set Bitmap RGB Channel

function SetRGBChannelValue(Bitmap: TBitmap; Red, Green, Blue: Integer): Boolean;
var
  i, j: Integer;
  rgbc: array[0..2] of Byte;
  c: TColor;
  r, g, b: Byte;
begin
  //If there is no change, exit:
  if (Red = 0) and (Green = 0) and (Blue = 0) then
  begin
    Result := False;
    Exit;
  end;

  for i := 0 to Bitmap.Height do
  begin
    for j := 0 to Bitmap.Width do
    begin
      // Get the old Color
      c := Bitmap.Canvas.Pixels[j, i];
      // Splitt the old color into the different colors:
      rgbc[0] := GetRValue(c);
      rgbc[1] := GetGValue(c);
      rgbc[2] := GetBValue(c);

      //Check that there is no "new" color while the addition
      //of the values:
      if not (rgbc[0] + Red < 0) and not (rgbc[0] + Red > 255) then
        rgbc[0] := rgbc[0] + Red;
      if not (rgbc[1] + Green < 0) and not (rgbc[1] + Green > 255) then
        rgbc[1] := rgbc[1] + Green;
      if not (rgbc[2] + Blue < 0) and not (rgbc[2] + Blue > 255) then
        rgbc[2] := rgbc[2] + Blue;

      r := rgbc[0];
      g := rgbc[1];
      b := rgbc[2];

      //set the new color back to the picture:
      Bitmap.Canvas.Pixels[j, i] := RGB(r, g, b);
    end;
  end;
  Result := True;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  SetRGBChannelValue(Image1.picture.Bitmap, 192, 79, 172);
end;