UK High Definition TV
The launch of HDTV or HD tv represents the most significant move forward in the specification of broadcasting and television ever since colour. For a flat panel widescreen television to receive and benefit from a HDsignal it must have a screen resolution of 1280 X pixels 720 pixels and be labelled HD Ready.
HD Ready – What is it?
If a flat panel tv carries the HD Ready label it will work with a HD signal and will be able to display a HD picture. TVs that are specified to meet the necessities of the HD Ready logo must have a minimum screen resolution of (1280 x 720 pixels) i.e. 720 vertical lines in 16:9 widescreen, where the signal received is either 720p/50 or 1080i/25 image formats and to be capable of accepting HD – the ’50’ or ’25’ is the amount of frames per second. They must also able to receive HD inputs by either DVI or HDMI and on Component Inputs.
Any TV that has a screen resolution of 1366 X pixels 768 pixels and is HD Ready will make use of internal scalers to alter 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 procedure of converting down or up is made by advanced software to fill the screen.
If a HD Ready television receives a full HD signal of resolution 1920 x pixels 1080 pixels the picture signal has to be interpolated or converted down to show the image. One to one mapping of the pixels is not possible.
‘HD Ready 1080p’ – What is it ?
A TV that has the ‘HD ready 1080P’ label is able to show a full 1080p signal because it has sufficient pixels for one to one pixel mapping. This can be done with out Interpolation. The resolution of a 1080p flat panel TV is 1920 pixels 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’. TVs 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 match the resolution of the 1080P widescreen TV. This is done using extremely complex algorithm sequences.
Full HD
Early HD tv’s didn’t boast the ‘HD Ready 1080p’ logo and may well not be compatible with this specification and may not display selected signal inputs.
Interlaced or Progressive
Interlaced picture have two fields that are alternated to make up a frame where every other line is shown on each frame. Hence the odd lines are on one field and the even lines are on the other field. When the two fields containing the odd and even lines are shown one after the other for each frame at two times the frame rate this is known as Interlacing.
Interlaced images 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 needs 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 standard definition LCD tvs and Plasma tvs. This is because the picture isn’t created with an electron scan like CRT tv’s so LCD televisions and Plama televisions don’t benefit from the interlaced picture signal. Flat panel widescreen televisions have internal processing to produce a progressive scanned image from a interlaced image – i.e. Deinterlacing.
Progressive scan delivers benefits.
This is also known as non-interlaced scanning. It is a method of storing, displaying or transmitting a moving image where all of the lines of every frame are shown sequentially rather than odd lines in one field and then even lines in the subsequent field as per Interlaced signals.
The vertical resolution when the frame rate is the same is greater for a progressive image than it is for an interlaced image and the picture is free of interlace artifacts, blurring, and greatly lower eye strain. With a progressive image it can be scaled to a higher resolution than an interlaced image giving a higher quality image. This is due to the deinterlacing that is necessary on an interlaced image preceding any scaling resulting in combing artifacts that are apparent.
720p/50 and 1080i/25 – What is the difference ?
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) image. However on interlaced moving pictures there are inter line twitters which reduce the subjective vertical resolution. The twitter is caused by the frames being a little different. Both 720p/50 and 1080i/25 are used by broadcasters depending on their inclination and bandwidth availability.
Progressive scanning 720p gives more fluid movement, especially on slow-motion, than an interlaced 1080i signal. But interlaced 1080i signals offer better static resolution. If the internal processing is competent enough a 1080i signal on a 1080 display will still look better than the 720p material. The best one depends on whether you are to display more static images or more moving pictures and what is more important to you.
When a HD Ready television receives a 1080p/50 signal it can change the image into a 1080i/25 image much easier than a full HDTV can change a 1080i signal into 1080p.
What are the advantages of 1080p/24?
The ultimate picture quality is available on films with a 1080p signal at 24 frames per second, when viewed via a BlueRay player on a flat screen high def television. The frame rate of 24 per second is identical to the original cinema film instead of being increased to 25 frames per second. The internal circuitry in the TV produces added middle frames so that the frame rate is increased to 48 or 72 producing smoother on screen motion.
Sources of HDTV
A HD Ready television can accept all current broadcast formats of 720p/50 or 1080i/25. HD is available on Freesat, Sky Digital HD, BT Vision, and Virgin media cable. The only sources of Full HD 1080P signals are Blueray players, Playstation 3 and by download on the internet. The games on an Xbox 360 are at 720P.
In conclusion
High definition enhances the viewing experience and makes TV more engaging. If you don’t propose to use a Blueray player, Playstation 3, or to download films from the internet then a HD ready tv will probably suffice. On the other hand if you need to future proof yourself against the possibility of future full high definition 1080p broadcasts then the full HD 1080p models are the ones to buy. Obviously, if you already possess, or are going to buy a Blueray player, Playstation 3 or to you are going to down load full high definition films then the full HD 1080p television is the logical choice.
Filed under: Television