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UK High Definition Television
The launch of HDTV or high definition tv represents the most important development in the specification of broadcasting and television ever since colour. For a flat panel widescreen tv to receive and gain 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?
For a television to be HD ready and show a high def. signal it must have a minimum screen resolution of 1280 x 720 pixels, where 720 is the amount of vertical lines. It must also be able to receive a signal of the specification of 720p/50 or 1080i/25; the amount of vertical lines is represented by the 720 and the 1080, Progressive or Interlaced signals are signified by the 'p' or 'i', and the number of frames per second is the 50 or 25. Connection for the hi def signal is by either DVI or HDMI and Component inputs.
For a 1366 x 768 pixels HD ready television, if it receives a 1080i signal then scalers inside the flat screen tv will down convert the image to fit the 768 lines flat panel television. This is done by means of complex algorithm sequences in the scaler which systematically crops the picture down to the resolution of the panel. If the signal is at 720p it follows that the signal will be slightly upscaled to fill the 768 vertical lines using complicated algorithms.
When a Full HD signal (1920 x 1080 pixels) is received by a HD Ready TV one to one pixel mapping is not possible due to insufficient pixels so the picture has to be interpolated to the screen resolution.
What is 'HD ready 1080P' ?
Any TV that carries the 'HD ready 1080p' is naturally capable of displaying a 'full' 1080P signal with sufficient pixels to offer true pixel-for-pixel mapping with no interpolation. A HD ready 1080p flat panel television has a picture resolution of (1920 x1080 pixels) i.e. 1080P, where '1080' is the vertical resolution of the image and the 'P' is for Progressive scan. HD ready 1080P is the maximum resolution available in the UK on HD televisions hence the 'full' term. These sets will display 1080p and 1080i images without distortion i.e. with 1:1 pixel mapping. They also boast HDMI or DVI HD input at 1080p HD and display signals that are at either 24 or 50 frames per second.
When a 1080p HD tv receives s 720p input it will upscale (or oversample) the signal to the resolution of the 1080p HDTV widescreen via complex internal software algorithms.
Full HD tv - What is it ?
Early high definition tv's didn't boast the 'HD Ready 1080p' logo and might not be compatible with this specification and may not show particular signal inputs.
What is an Interlaced 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 contains the even lines. Interlacing is when these two fields are shown in sequence at two times the rate of the actual frame and at half the resolution.
When a picture is interlaced, moving images on video appear to have smoother movement because each field of the frame are shot at different times. The system of picture interlacing was in the first place used to enhance the quality of the picture on tube televisions using the equivalent amount of bandwidth for the broadcast signal.
The UK broadcast standard is known as PAL which operates with 25 full frames per second or 50 fields per second. Interlacing the signal means that half the picture information is in each field so half the bandwidth is required for broadcasting in comparison to a Progressive signal at 50 full frames per second.
CRT (Cathode Ray Tube) tv or the old CRT tvs are able to show interlaced images made for TV or on a video camera because they have an electron scan. Flat panel lcd TVs and plasma TVs aren't able to show such signals without the use of progressive scanning or deinterlacing.
Progressive scan delivers benefits.
This is a method to show, transmit, and store a moving image. Each frame has all of the lines rather than even lines or odd lines as with an Interlaced signal and they are displayed in sequence.
The benefits of Progressive Scanning is that there is a greater vertical resolution than on Interlaced pictures at the same frame rate without blurring, interlace artifacts, and reduced eye strain. It is also possible to scale to a higher resolution than it is with equivalent interlaced sources. For the reason that interlaced signal sources have to be deinterlaced before scaling with observable combing artifacts, Progressive scanned full pictures give the best results when scaling.
720p/50 and 1080i/25 - What is the difference ?
A 1080i/25 (1,920x1080 pixel resolution) interlaced signal has slightly better horizontal resolution on still pictures than a progressive scanned 720p/50 (1,280x720 pixel resolution) picture. 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 motion, particularly on slow-motion, than an interlaced 1080i signal. But interlaced 1080i signals give better static resolution. If the internal processing is competent enough a 1080i signal on a 1080 display will still appear superior than the 720p material. The best one depends on whether you are to display more static images or more moving images and what is more important to you.
When a HD Ready TV receives a 1080p/50 signal it can convert the picture into a 1080i/25 image much easier than a full HDTV can convert a 1080i signal into 1080p.
What is 1080p/24 ?
The definitive picture quality is available on films with a 1080p signal at 24 frames per second, when viewed via a Blu Ray player on a flat panel high def tv. The frame rate of 24 per second is equal to the original cinema film instead of being increased to 25 frames per second. The internal circuitry in the TV produces extra middle frames so that the frame rate is increased to 48 or 72 producing smoother on screen motion.
Sources of HDTV
A HD Ready tv can accept all current broadcast formats of 720p/50 or 1080i/25. HD is obtainable on Freesat, Sky Digital HD, BT Vision, and Virgin media cable. The only sources of Full HD 1080P signals are Blu ray players, Playstation 3 and by download on the internet. The games on an Xbox 360 are at 720P.
Conclusion
High definition television delivers an enhanced subjective picture quality that makes the reason for HD compelling. If you have possession of, or expect to own, a Playstation 3, a Blu ray player, or download full HD films from the internet then a Full HD 1080p tv is the best choice. Otherwise a HD Ready television will be suitable. At the same time as these recommendations deal with today's available options they don't allow for the possibility of future broadcasts in Full 1080p HD. If you would like to be entirely sure that you protect your purchase against this scenario then buy a Full 1080p HD flat panel TV.
About the Author Before you buy any electrical products on the web, make sure you check Armadeus Cornelius' excellent website for more information on HD Ready TV, and also Discount Flat Screen TVs
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