procedure TfmMain.RGBtoHSV(Red, Green, Blue: Byte; var Hue: Integer; var Saturation, Value: Byte);
var
  Maximum, Minimum: Byte;
  Rc, Gc, Bc: Single;
  H: Single;
begin
  Maximum := Max(Red, Max(Green, Blue));
  Minimum := Min(Red, Min(Green, Blue));
  Value := Maximum;
  if Maximum <> 0 then
    Saturation := MulDiv(Maximum - Minimum, 255, Maximum)
  else
    Saturation := 0;
  if Saturation = 0 then
    Hue := 0 // arbitrary value
  else
  begin
    Assert(Maximum <> Minimum);
    Rc := (Maximum - Red) / (Maximum - Minimum);
    Gc := (Maximum - Green) / (Maximum - Minimum);
    Bc := (Maximum - Blue) / (Maximum - Minimum);
    if Red = Maximum then
      H := Bc - Gc
    else if Green = Maximum then
      H := 2 + Rc - Bc
    else
    begin
      Assert(Blue = Maximum);
      H := 4 + Gc - Rc;
    end;
    H := H * 60;
    if H < 0 then
      H := H + 360;
    Hue := Round(H);
  end;
end;

function TfmMain.HSVtoRGB(H:Integer; S, V: Byte):TColor;
var
  ht, d, t1, t2, t3:Integer;
  R,G,B:Word;
begin
  if S = 0 then
   begin
    R := V; G := V; B := V;
   end
  else
   begin
    ht := H * 6;
    d := ht mod 360;

    t1 := round(V * (255 - S) / 255);
    t2 := round(V * (255 - S * d / 360) / 255);
    t3 := round(V * (255 - S * (360 - d) / 360) / 255);

    case ht div 360 of
    0:
      begin
        R := V; G := t3; B := t1;
      end;
    1:
      begin
        R := t2; G := V; B := t1;
      end;
    2:
      begin
        R := t1; G := V; B := t3;
      end;
    3:
      begin
        R := t1; G := t2; B := V;
      end;
    4:
      begin
        R := t3; G := t1; B := V;
      end;
    else
      begin
        R := V; G := t1; B := t2;
      end;
    end;
   end;
  Result:=RGB(R,G,B);
end;