The introduction of HDTV or high def television symbolizes the most important development in the specification of broadcasting and TV ever since colour. For a flat panel widescreen television to receive and gain from a high definition signal it must have a screen resolution of 1280 X pixels 720 pixels and be labelled HD Ready.
What does ‘HD ready’ mean ?
If a flat panel television 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 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 image formats and to be capable of accepting HD – the ’50′ or ’25′ is the quantity 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-66 pixels x 768 pixels it will use 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 image (or oversample) to 768 vertical lines. These processes are carried out using advanced software that either crops the pictureor oversamples the image to fill the screen.
Most HD ready televisions don’t have a sufficient amount pixels to give true pixel-for-pixel mapping without interpolation of the higher HD resolution (1920 x 1080 pixels).
‘HD Ready 1080p’ – What is it ?
If a plasma tv or lcd tv has a ‘HD ready 1080p’ badge it has an adequate amount of pixels to show the full 1080p signal with pixel for pixel mapping with no interpolation. A 1080p flat screen lcd television or plasma television is’20 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 tv is the highest picture resolution in the UK for high definition and thus the term ‘full’. Any plasma television or lcd television with this resolution can show 1080i and 1080p signals without up or down scaling, and by way of 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 represent the number of frames per second.
If a flat panel 1080P Television receives a 720P picture the signal is ‘oversampled’ to suit the resolution of the 1080P widescreen Television. This is completed using extremely complex algorithm sequences.
What is a Full HD TV ?
Older full HD flat panel tv’s may possibly not fulfill all ‘HD Ready 1080P’ requirements.
What is an Interlaced or Progressive picture ?
Interlaced picture have two fields that are alternated to produce a frame where every other line is displayed on each frame. So 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 consecutively for each frame at twice the frame rate this is known as Interlacing.
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 needs to scan the picture 50 times per second whilst the interlaced scanning process works at half of that speed.
CRT (Cathode Ray Tube) tv or the old glass TVs are able to display interlaced images made for television or on a video camera because they have an electron scan. Flat panel lcd tvs and plasma tvs aren’t able to display such signals without the use of progressive scanning or deinterlacing.
The benefits of progressive scanning
This is a method to display, transmit, and store a moving image. Every frame has all of the lines rather than even lines or odd lines as with an Interlaced signal and they are shown in sequence.
Progressive scan has the benefit of higher vertical resolution than interlaced images with the same frame rate and no interlace artifacts or blurring, and hence less eye strain. Also better results are possible for scaling to higher resolutions than the equivalent interlaced sources. For the finest scaling results full frames work the best but interlaced video sources have to be deinterlaced prior to being scaled and this can produce very noticeable combing artifacts.
720p/50 and 1080i/25 – What is the difference ?
A 1080i/25 (1,920×1080 pixel resolution) interlaced signal has to some extent better horizontal resolution on still pictures than a progressive scanned 720p/50 (1,280×720 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 slightly different. Both 720p/50 and 1080i/25 are used by broadcasters depending on their inclination and bandwidth availability.
Smoother movement is produced with 720p progressive scanned images, above all on slow-motion, compared to 1080i interlaced pictures. Better still pictures 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 ought to choose, will depend on the type of images being predominantly displayed, either static or moving, and your preferences.
When a HD Ready tv receives a 1080p/50 signal it can convert the picture into a 1080i/25 picture much easier than a full HDTV can change a 1080i signal into 1080p.
The benefits of a 1080p/24 signal.
Since the films that are shown in cinemas are created at 24 frames per second a signal is in its purest form at this frame rate. Films are obtainable on Blu ray disc at 24 frames per second with the purpose of givingthe ultimate picture quality when displayed on widescreen full HD tvs. When a full hd television receives a 1080p/24 signal it creates additional middle frames, which are inserted between the original ones to enhance the frame rate to 48 or 72 frames per second giving more fluid motion.
Sources of HDTV
All HD TV broadcasts are now 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 high definition television are by satellite on Freesat and Sky digital hd, and on 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 can 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 propose to use a Blu ray player, Playstation 3, or to download films off the internet then a HD ready tv will almost certainly suffice. Then again if you want to future proof yourself against the chance of future full HD 1080p broadcasts then the full HD 1080p models are the ones to buy. Clearly, if you already have, or are going to buy a Blu ray player, Playstation 3 or to you are going to down load full HD films then the full HD 1080p television is the sensible choice.
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