High Definition Television in the UK
HD TV, where the HD is for high definition tv (or high def tvs). This is most likely the most significant revolution in broadcasting since Television changed to colour from black & white. HDTV uses widescreen digital flat panel televisions such as a Plasma televisions and LCD televisions where the screen resolution is at least 1280 pixels x 720 pixels or HD Ready. There are 2 types of high def broadcasting, 720p/50 and 1080i/25.
What makes a Television ‘HD Ready’ ?
Any television that is HD Ready is capable of receiving and displaying a HD picture. To meet this specification the television should have a picture resolution of at least 1280 pixels x 720 pixels. They have got to be able to receive a signal that is 1080i/25 or 720p/50, where the 1080 or 720 is the number of vertical lines, the ‘i’ is for an interlaced picture and the ‘p’ is for a progressive scan picture, and the 25 and the 50 are the number of frames displayed each second. Furthermore the televisions must have either DVI or HDMI and Component signal input connectors.
Every TV that has a screen resolution of 1366 x pixels 768 pixels and is HD Ready will make use of internal scalers to change a 1080i signal down to the 768 lines; if it receives a 720p signal the internal circuits will upscale the image to 768 lines. The method of converting down or up is completed by highly developed software to fill the screen.
Most HD ready televisions do not have sufficient pixels to give true pixel-for-pixel mapping without interpolation of the higher HD resolution (1920 x 1080 pixels).
What does ‘HD ready 1080P’ mean ?
A television that has the ‘HD ready 1080P’ label is capable of showing a full 1080p signal because it has enough pixels for one to one pixel mapping. This can be done with out Interpolation. The resolution of a 1080p flat screen TV is 1920 x 1080 pixels or 1080P. The 1080 signifies the vertical resolution and the P is progressive scan. This is the maximum resolution existing in the United Kingdom on high definition televisions so that’s why the term ‘full’. Televisions with this resolution are capable of displaying 1080p and 1080i signals without any distortion and with exact pixel for pixel mapping. They must also be equipped with DVI or HDMI inputs for 1080P signals at either 24 or 50 frames per second.
If a flat panel 1080P TV receives a 720P image the signal is ‘oversampled’ to suit the resolution of the 1080P widescreen TV. This is completed using very complex algorithm sequences.
Full HD tv – What is it ?
Early High Def. tv’s didn’t hold the ‘HD Ready 1080p’ logo and may not be compatible with this specification and may not display certain signal inputs.
Interlaced Picture or Progressive Picture ?
On an Interlaced Picture the scan lines of a frame are arranged in two fields each. One of the two fields includes the odd lines and the other field holds the even lines. Interlacing is when these two fields are shown in sequence at double the rate of the actual frame and at half the resolution.
Interlaced pictures on video have more fluid motion due to each field being shot at a different time. Interlacing initially benefited CRT (cathode ray tube) tv’s by improving the picture quality and using the same amount of broadcast bandwidth.
Televisions in the UK have a PAL picture system that have a rate of 25 frames per second or 50 fields per second. An Interlaced signal uses half the bandwidth of a Progressive signal i.e. the progressive scanning process has to scan the picture 50 times per second whilst the interlaced scanning process works at half of that speed.
Interlaced pictures on recordings made for television or with a video camera aren’t able to be displayed on normal definition LCD tvs and Plasma televisions. This is for the reason that the picture isn’t created with an electron scan like CRT televisions so LCD TVs and Plasma tvs don’t gain from the interlaced picture signal. Flat panel widescreen televisions have internal processing to make a progressive scanned picture from a interlaced image – i.e. Deinterlacing.
Progressive scan delivers benefits.
This is in addition known as non-interlaced scanning. It is a technique of storing, displaying or transmitting a moving image where all of the lines of every frame are shown sequentially instead of odd lines in one field and then even lines in the next field as per Interlaced signals.
Progressive scan has the advantage of superior vertical resolution than interlaced images with the same frame rate and no interlace artifacts or blurring, and thus less eye strain. Also better results are possible for scaling to higher resolutions than the comparable interlaced sources. For the best scaling results full frames work the best whereas interlaced video sources have got to be deinterlaced prior to being scaled and this can cause extremely noticeable combing artifacts.
The differences between 720p/50 and 1080i/25 formats
A 1080i/25 (1,920×1080 pixel resolution) interlaced signal has slightly better horizontal resolution on still pictures than a progressive scanned 720p/50 (1,280×720 pixel resolution) picture. But on interlaced moving pictures there are inter line twitters which diminish the subjective vertical resolution. The twitter is caused by the frames being slightly different. Both 720p/50 and 1080i/25 are used by broadcasters depending on their preference and bandwidth availability.
Smoother movement is produced with 720p progressive scanned pictures, particularly on slow-motion, compared to 1080i interlaced images. Better still images are produced with interlaced 1080i signals. By means of good quality built in processing a 1080i signal will appear superior on a 1080 television compared to a 720p source. The one you should choose, will depend on the type of pictures being predominantly displayed, either static or moving, and your preferences.
It is easier to convert a progressive signal (i.e. 1080p/50) into an interlaced format, such as 1080i/25, than it is to convert an interlaced format into a progressive format.
What are the advantages of 1080p/24?
This is 1080p at 24 frames per second. This gives the definitive picture quality with the 1080p picture decoded straight from the Blu Ray disc at 24 frames per second, and then sent to the flat screen HD TV. The 24 frames per second is the same rate as the original cinema film. The TV will then create additional frames to multiply to either 48 or 72 frames per second creating middle frames that make the image more fluid.
Sources of high def.
All HD tv broadcasts are at present at either 720p/50 or 1080i/25 and are can be viewed to their full benefit on HD Ready widescreen tv’s. Currently the only broadcasters of high def. television are by satellite on Freesat and Sky digital hd, and over the internet on BT vision, and on cable by Virgin media. The only sources of Full HD 1080p are either by download over the internet and on Blu ray. The Xbox 360 be capable of give a 720p/50 image for games and the Playstation 3 can offer a 1080p image for games.
Conclusion
High definition enhances the viewing experience and makes television more engaging. If you don’t expect to use a Blu ray player, Playstation 3, or to download films off the webthen a HD ready tv will almost certainly suffice. However if you would like to future proof yourself against the possibility of future full high definition 1080p broadcasts then the full HD 1080p models are the ones to purchase. Clearly, if you already own, or are going to buy a Blu ray player, Playstation 3 or to you are going to down load full high definition films then the full HD 1080p television is the sensible choice.
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