Picture-in-picture the screen. Televisions at the time were still analog format, and earlier versions of the PiP implemented in analog were too costly. New digital technology allowed the second video signal to be digitized and saved in a digital memory chip then replayed in a mini version. While the new technology was not good enough for color or full-screen viewing, it did provide a low-cost PiP feature. The Blu-ray Disc and HD DVD specifications included picture in picture, allowing viewers to see, say, the director's comment on a film they are watching. All of the Blu-ray Disc titles in 2006 and
Optical medium Optical medium An optical medium is material through which electromagnetic waves propagate. It is a form of transmission medium. The permittivity and permeability of the medium define how electromagnetic waves propagate in it. The medium has an "intrinsic impedance", given by where formula_2 and formula_3 are the electric field and magnetic field, respectively. In a region with no electrical conductivity, the expression simplifies to: For example, in free space the intrinsic impedance is called the characteristic impedance of vacuum, denoted "Z", and Waves propagate through a medium with velocity formula_6, where formula_7 is the frequency and formula_8 is the wavelength