Glossary » H

H.264 is the most advanced form of the MPEG-4 standard. (Part 10). It is also know as AVC (Advanced Video Codec). It’s designed to offer first-rate video quality at substantially lower bit-rates (typically half, or less) than existing standards such as MPEG-2 (H.262). A benefit is that it enables broadcasters to offer more channels without compromising image quality. Its use would also enable studios to fit more onto a next generation medium such as HD-DVD or Blu-ray. Perhaps the best known current use is the 5th generation Apple iPod, which uses it as its default video format.

A hardware driver is a piece of software used to make sure your hardware is speaking a language that can be understood by every other component that needs to interact with it. A driver may take a simple command and convert it to a more complex command to take advantage of the advanced capabilities of a component. Drivers are often updated to correct bugs, to improve performance or add new features.

HDCP stands for High-Bandwidth Digital Content Protection. This is a standard, originally developed by Intel, for protecting digital content sent over DVI or HDMI from a source such as a DVD player, PC or set-top box to a display such as a plasma, LCD or projector. It is a form of DRM and the intention is to prevent digital copying of high-definition material to prevent piracy. The source queries the the display and any relevant components for HDCP compliance and authentication keys are swapped between the devices before the audio and video is presented. The integrity of the connection is checked every few seconds. For HDCP content to display correctly, either the DVI or HDMI connection on the source and the display have to be HDCP compliant. For example, if you attach a Blu-ray or HD-DVD player to a non-compliant screen it will not display the high resolution content and a down-sampled image will be displayed. In Europe, for a manufacturer to use the HD Ready logo on its products, HDCP compliance is required. In a PC, the Blu-ray or HD-DVD drive, the graphics card and the display all need to be HDCP compliant. HDCP compliant graphics card from ATI and NVIDIA are expected to be available mid-2006.

HDMI stands for High Definition Multimedia Interface, a digital interface that carries uncompressed video and audio. Think of it as a digital SCART for the 21st century. With 5Gbps of bandwidth, HDMI is able to deliver high-definition pictures and multi-channel audio down a single cable at the same time. This also simplifies connectivity and cuts down on clutter, replacing the three cables that are needed for Component video and the six analogue cables required for sending high-resolution digital audio (DVD-Audio and SACD) signals. The connector is physically different to DVI, but is electrically similar. Both offer the same picture quality but HDMI adds audio into the mix as well. HDMI connections can now be found in an increasing number of consumer DVD players and displays. Its presence is one of the requirements for a display to be deemed ‘HD Ready’. It’s also found on some integrated surround amplifiers and will be featured on Sky’s forthcoming HD set-top box and on Sony’s PlayStation 3.

An SI unit used to measure the number of repetitions of a regular occurrence in one second. One Hz is equal to one cycle per second. Named after the German Physicist Heinrich Hertz.

Hidden Surface Removal involves discarding data concerning parts of a 3D scene that won’t be visible in the final rendered image before it has been processed. This saves your graphics card wasting valuable resources creating things that will eventually be hidden anyway.

Graphical representation of the tonal range in an image, which can be used to identify the level of detail in highlights or shadows. Some cameras offer a histogram during playback only, while others more usefully offer a live histogram during image composition, allowing you to make instant exposure adjustments.

The distance (in mm) between one shadow mask phosphor dot and the next one of the same colour, measured horizontally. Often quoted by CRT manufacturers because it is always a smaller than the standard dot pitch. See grille pitch and dot pitch.

A measure, in KHz, of how many lines a monitor draws per second in a raster formation from the top left to the bottom right of the screen. The horizontal frequency is directly related to the number of lines and the vertical refresh rate, so an image made up of many lines that is also refreshed very quickly will need a suitably high horizontal frequency.

Square connector used for mounting accessories like flash guns. Hotshoes may all have the same basic shape and main connector, but additional proprietary contacts normally limit a camera to using a flash from the same manufacturer.

A measure of colour based on the relative strengths of the red, green and blue components. It is that quality of colour which cannot be accounted for by differences in luminance or saturation.