 In addition, the application of gamma correction to the signals further complicates the situation (display tubes have, approximately, a square law characteristic with γ ≈ 2.2).As shown below, it is beneficial, but not sufficient, to shape the luminance response to simulate that of the NTSC (PAL or SECAM) luminance characteristic (by, for example, placing an optical filter in front of the luminance tube to pass light with the required luminosity function, or by a special dichroic surface which reflects light to the luminance tube with the required luminosity function).For a basic 3-colour system the wideband luminance signal (Y'), for NTSC, PAL and SECAM, is given by