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High Definition Digital TV
HD TV, where the HD is for high definition television (or high def tvs). This is probably the most significant revolution in broadcasting since TV changed to colour from black & white. HDTV uses widescreen digital flat panel tvs such as a Plasma televisions and LCD tv's where the resolution is at least 1280x720 pixels or HD Ready. There are 2 types of HD broadcasting, 720p/50 and 1080i/25.
What does 'HD ready' mean ?
If a flat screen tv carries the HD Ready label it will operate with a HD signal and will be able to show a HD picture. tvs that are specified to meet the requirements of the HD Ready logo must have a minimum picture resolution of (1280 pixels x 720 pixels) i.e. 720 vertical lines in 16:9 widescreen, where the signal received is either 720p/50 or 1080i/25 picture formats and to be capable of accepting HD - the '50' or '25' is the amount of frames per second. They must also able to accept HD inputs by either DVI or HDMI and on Component Inputs.
If a HD Ready tv has a screen resolution of 1366 x 768 pixels it will make use of internal scalers that will convert the signal down to 768 vertical lines when it receives a 1080i signal. With a 720p signal the television has to upscale the picture (or oversample) to 768 vertical lines. These processes are carried out using advanced software that either crops the imageor oversamples the image 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 altered down to show the image. One to one mapping of the pixels is not feasible.
What does 'HD ready 1080P' mean ?
If a plasma television or lcd television has a 'HD ready 1080p' badge it has an adequate amount of pixels to display the full 1080p signal with pixel for pixel mapping without interpolation. A 1080p flat panel lcd tv or plasma television is 1920 x 1080 pixels where the 1080 is the vertical resolution and the 'p' is for progressive scan. A HD Ready 1080p widescreen lcd tv or plasma television is the highest picture resolution in the UK for high definition and hence the term 'full'. Any plasma television or lcd tv with this resolution can display 1080i and 1080p signals without up or down scaling, and including one to one pixel mapping. Connectivity must be by either HDMI or DVI inputs. HD Ready 1080p full hd tv's must be able to display a 1080p/24 or 1080p/50 signal where the 24 and the 50 stand for the number of frames per second.
If a 720p signal is received by a 1080p tv it is oversampled (or upscaled) to fill the resoltion of the 1080p HD television by means of advanced software.
Full HD television - What is it ?
Older full HD flat panel tv's may not fulfill all 'HD Ready 1080P' requirements.
Interlaced Picture or Progressive Picture ?
An Interlaced Image involves arranging the scan lines of one frame into two fields where one field contains the odd lines and an additional field contains all of the even lines - so each field has half the resolution. The two fields of the frame are alternately displayed in sequence at a rate that is twice as fast as the actual frame rate, this is known as Interlacing.
One of the advantages of Interlacing is that when footage is shot of a moving picture each of the fields of a frame are taken at separate times making motion that appears more fluid. Picture Interlacing is a system that was initially used to improve the picture quality of a signal on CRT televisions without using extra signal bandwidth.
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.
Standard definition LCD tvs and Plasma tvs displays aren't able to operate on an interlaced mode for footage shot with a TV or video camera. Because LCD tv displays and Plasma tv displays do not have an electron scan to create an image they cannot benefit from interlacing. So internal processing in the flat panel tv creates a progressive scan image from the interlaced signal.
The advantagess of progressive scanning
This is a method to show, transmit, and store a moving image. Every frame has all of the lines instead of even lines or odd lines as with an Interlaced signal and they are shown in sequence.
The vertical resolution when the frame rate is the same is greater for a progressive image than it is for an interlaced picture and the picture is free of interlace artifacts, blurring, and a good deal 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 required on an interlaced image preceding any scaling resulting in combing artifacts that are obvious.
What is the difference between the 720p/50 and 1080i/25 formats?
On static images a 1080i/25 (1920 X pixels 1080 pixels) produces a a little higher horizontal picture resolution than a 720p/50 (1280 x pixels 720 pixels) image. Moving images on an interlaced picture have a lower subjective line resolution because of line twitter or artifacts caused by the fields being somewhat different that make up a frame. Broadcasters tend to opt for 1080i/25 over 720p/50 since it requires a lesser amount of bandwidth, but both systems are used for high definition TV broadcasts.
A progressively scanned 720p will create smoother image movement than a 1080i interlaced signal, above all on slow motion. With good quality internal processing a 1080i appears to have a better picture than a 720 signal. The best operating mode will depend on whether the screen is being used more with still pictures than moving images, and on the quality of the internal processing.
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 ultimate picture quality with the 1080p picture decoded straight from the BlueRay disc at 24 frames per second, and then sent to the flat screen HD Television. The 24 frames per second is the same rate as the original cinema film. The TV will then produce additional frames to multiply to either 48 or 72 frames per second creating middle frames that make the image more fluid.
HDTV Sources
All HD TV broadcasts are currently at either 720p/50 or 1080i/25 and are can be viewed to their full benefit on HD Ready widescreen tv's. At this time the only broadcasters of HD TV are by satellite on Freesat and Sky digital hd, and on the web 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 Blueray. The Xbox 360 can give a 720p/50 image for games and the Playststion 3 can create a 1080p image for games.
In 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 Blueray player, or download full HD films from the internet it follows that a Full HD 1080p television is the best option. If not a HD Ready television will be suitable. Whilst 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 absolutely sure that you protect your purchase against this scenario then buy a Full 1080p HD flat screen TV.
About the Author For virtually 20 years Armadeus Cornelius has built a wealth of knowledge in the electrical industry. For additional advice and information go to his web site for HD Ready TV. Alternatively you can goto his on-line electrical store for discount on HD Televisions.
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