function Farbzahl(bm: TBitmap): integer; 
var 
  bits: TBits; 
  hlp: TBitmap; 
  scan: ^Integer; 
  x, y: Integer; 
begin 
  hlp := TBitmap.Create; 
  hlp.pixelFormat := pf24bit; 
  hlp.height := bm.height; 
  hlp.width := bm.width; 
  hlp.canvas.draw(0, 0, bm); 
  Result := 0; 
  bits := TBits.Create; 
  bits.Size := 16777216; 
  hlp.pixelFormat := pf32bit; 
  for y := 0 to hlp.height - 1 do begin 
    scan := hlp.ScanLine[y]; 
    for x := 0 to hlp.width - 1 do begin 
      if not bits[scan^] then begin 
        inc(Result); 
        bits[scan^] := true; 
      end; 
      inc(scan); 
    end; 
  end; 
  bits.Free; 
  hlp.Free; 
end; 

 
// Beispielaufruf 
procedure TForm1.Button10Click(Sender: TObject); 
var az: integer; 
begin 
  az := Farbzahl(Image1.picture.bitmap); 
  if az = 0 then showmessage('Fehler') 
  else showmessage('Dieses Bild hat ' + inttostr(az) + ' Farben.'); 
end;