High definition (HD or HDTV) is a different standard of digital television broadcasting which offers sharper, more detailed pictures and surround sound.
Only viewers with an "HD Ready" television set, a special HD set top box receiver and reception of a high definition service will experience true HD programming. High definition programmes must also be specially shot.
It requires an entirely separate broadcast stream from current standard definition (SD) broadcasting It has a 16:9 aspect ratio, which is the same as a movie theatre screen, and transmits in either 720 or 1080 formats.
The two HD formats currently in use, 720p and 1080i, the number referring to the vertical line resolutioon of the picture.
1080 has a larger number of displayed lines, and is interlaced as with standard definition TV, whilst 720 is progressively scanned, similar to a PC display.
Most channels in the UK are based on 1080i, and Channel 4 will be using only this format.
Channel 4 HD will be show a proportion of its acquired programmes with 5.1 surround sound. 5.1 surround sound consists of 6 channels — a front left, center (for dialogue), front right, rear left, rear right and a subwoofer channel for low frequency effects. This is similar to the large number of DVD titles in standard definition which are now available.
The Channel 4 HD service will be available on channel 140 via Sky HD only, so you will need to have a Sky HD box and viewing card, as well as an HD ready TV to view.
Channel 4 will only transmit using 1080i on channel 140 on Sky HD.
Channel 4 HD will be a direct simulcast of the core Channel 4 schedule. A proportion of the programmes will have been orginally made in the HD format, these will include some of our well know US series and films as well as some Channel 4 commissioned programmes. The Channel 4 Group is committed to increasing its investment in HD production and acquiring programmes in the HD format. We fully intend to increase the proportion of our schedule which is made in high definition over time. The remaining non-HD programmes will be up-converted from the SD source material.
Currently there is no allocated spectrum or capacity for a Freeview HD service, which requires a large amount of bandwidth. Once the analogue services are switched off, Ofcom may make space available for HD channels. So unfortunately, for the time being, Channel 4 HD will only be available on Sky HD but we are hopeful that it will be made available on other platforms in future.
We hope to get these services on the channel as soon as we can – but probably they won’t be available at inception.
We’ve no information on that at the moment, so watch this space!
Initially only some acquired programmes will have 5.1 surround sound (Ugly Betty for example). As more programmes are commissioned in HD, that number will increase.
Original HDTV programming is made in the 16x9 (1.78) aspect ratio, which fits the dimensions of HDTVs which are Widescreen. However, many theatrically released films are made in either the 1.85 or 2.35 aspect ratio, which is even wider than the 16x9 (1.78) aspect ratios of HDTVs. Therefore, when viewing these films on an HDTV (if presented in their original theatrical aspect ratio) - you will see black bars on your 16x9 screen. However, the bars will be less pronounced than if the same movie is viewed letterboxed on a standard 4x3 set.
For upconverted 4x3 programmes , these will be seen with black bars on the left and right.
