Glossary of Terms

HDTV (High Definition Video)

This high resolution 16:9 ratio, progressive scan format can now be recorded to standard mini DV cassettes. Consumer high definition cameras are becoming available but this is currently an expensive, niche market. It is also possible to capture video using inexpensive webcams. These normally connect to a computer via USB. While they are much cheaper than DV cameras, webcams offer lower quality and less flexibility for editing purposes, as they do not capture video in DV format. Digital video is available on many portable devices from digital stills cameras to mobile phones. This is contributing to the emergence of digital video as a standard technology used and shared by people on a daily basis.

MPEG

MPEG, the Moving Picture Experts Group, overseen by the International Standards Organization (ISO), develops standards for digital video and digital audio compression. MPEG‐1 with a default resolution of 352x240 was designed specifically for Video‐CD and CD‐media and is often used in CD‐ROMs.

MPEG‐1 audio layer‐3 (MP3) compression evolved from early MPEG work. MPEG1 is an established, medium quality format (similar to VHS) supported by all players and platforms. Although not the best quality, it will work well on older specification machines.

MPEG‐2 compression (as used for DVD movies and digital television set‐top boxes) is an excellent format for distributing video, as it offers high quality and smaller file sizes than DV. Due to the way it compresses video MPEG‐2‐encoded footage is more problematic to edit than DV footage. Despite this, MPEG2 is becoming more common as a capture format. MPEG 2 uses variable bit rates allowing frames to be encoded with more or less data depending on their contents. Most editing software now supports MPEG2 editing. Editing and encoding MPEG2 requires more processing power than DVD and should be done on well specified machines. It is not suitable for internet delivery.

MPEG‐4 is a set of video and audio standards intended to deliver quality video over limited bandwidths that also support a range of other media types such as text, still image and animation. MPEG‐4 offers high quality, scalable streaming over a range of bandwidths, including those provided by mobile networks. The standards also include components and elements that allow the viewer to interact with the picture on the screen or to manipulate individual elements in real time. The MPEG4 format is a container for various versions called layers. There are different implementations, some of which are proprietary and not compliant with the ISO MPEG4 standard. It was initially thought that MPEG4 would become the default format for video over the internet. With support from Apple, Real Networks and others this may still be the case. However, problems over licensing costs and the lack of digital rights management in the standard made many content providers slow to embrace it. These issues are being tackled but it also faces competition from proprietary formats such as Windows Media. MPEG4 is beginning to be supported in other areas such as mobile video (3G), mobile television, set‐top boxes and video on demand (VOD).

Gigabyte (GB)

A gigabyte equals about 1,000 megabytes (MB). A Blu‐ray Disc capable of recording 50 GB therefore stores about 50,000 Megabytes

Layer

In Blu‐ray Disc, data is recorded on a single side of the disc. However, a disc can store two data layers, both at the same side. The readout or recording laser of the Blu‐ray Disc device will first read from or record to one layer, and then re‐focuses on the second layer. All this is done automatically without any user interference. A double layer Blu‐ray Disc can store upto 50 GB of data.

SDTV

It stands for “Standard Definition Television.” Generic term used for conventional television sets, based on the NTSC or PAL standards. SD television consists of 480 to 570 visible lines.

Numerical Aperture and Resolution

The numerical aperture of a microscope objective is a measure of its ability to gather light and resolve fine specimen detail at a fixed object distance.

Image‐forming light waves pass through the specimen and enter the

objective in an inverted cone as illustrated in Figure 1. A longitudinal slice of this cones of light shows the angular aperture, a value that is determined by the focal length of the objective. The angle μ is one‐half the angular aperture (A) and is related to the numerical aperture through the following equation:

Numerical Aperture (NA) = n (sin μ)

Where n is the refractive index of the imaging medium between the front lens

of the objective and the specimen cover glass, a value that ranges from 1.00 for air to 1.51 for specialized immersion oils. Many authors substitute the variable μ for μ in the numerical aperture equation. From this equation it is obvious that when the imaging medium is air (with a refractive index, n = 1.0), then the numerical aperture is dependent only upon the angle μ whose maximum value is 90°. The sin of the angle μ, therefore, has a maximum value of 1.0 (sin90° = 1), which is the theoretical maximum numerical aperture of a lens operating with air as the imaging medium (using “dry” microscope objectives).

THE BLUE LASER

The laser used with the Blu‐ray disc has a wavelength of 405nm.Though the red and the green lasers were discovered much earlier, it was only in 1996 that the blue laser was discovered. Actually, the wavelength 405nm would correspond to the blue‐violet part of the visible light, in the spectrum. This achievement is attributed to the efforts of Shuji Nakamura of Nichia Corporation, Japan. The device utilizes a GaN diode as its laser source. The operating current is kept between 60mA and 70mA for optimum performance.

For writing into the disc, the power of the laser used is about 6mW. For reading from the disc, much lesser power is required, only about 0.7mW.The GaN source can give a power of about 65mW. So, it is an ideal choice for the laser source to be used with the Blu‐ray disc. Due to the much lower wavelength involved, the amorphous mark size (bit size) is small, leading to higher storage capacity on disc of the same size, about five to six times the capacity of a DVD.

A blue laser operates in the blue range of the light spectrum, ranging from about 405nm to 470nm. Most blue laser diodes use indium gallium nitride as the material to create the laser light, although the amount of indium included in the material varies. (Some blue laser diodes use no indium.) Some manufacturers create blue LEDs (light-emitting diodes), which create light in a manner similar to lasers with silicon carbide.

Blue laser beams have a smaller spot size and are more precise than red laser beams, which lets data on blue laser optical storage discs be stored more densely. The spot size of a laser beam is one determining factor, along with the materials in the optical disc and the way the laser is applie d to the disc, in the size of the pits the laser makes on an optical disc. Laser beams with larger spot sizes typically create larger pits than those with smaller pit sizes. Blue lasers are desirable because blue light has the shortest wavelength among visible light.

A blue laser operates at a shorter wavelength of about 405nm than a red laser at about 650nm. A nanometer (nm) is one-billionth of a meter, one-millionth of a millimeter, and one-thousandth of a micron. One inch is equal to about 25.4 million nanometers. A human hair is about 50,000nm wide.