HDTV Basics
HD TV, where the HD is for high definition tv (or high def tvs). This is possibly the most significant revolution in broadcasting since Television changed to colour from black & white. HDTV uses widescreen digital flat panel tvs such as a Plasma televisions and LCD tv’s where the screen resolution is at least 1280×720 pixels or HD Ready. There are two types of high def broadcasting, 720p/50 and 1080i/25.
HD Ready – What is it?
For a tv to be HD ready and show a high def. signal it must have a minimum screen resolution of 1280 x pixels 720 pixels, where 720 is the number 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 HD signal is by either DVI or HDMI and Component inputs.
Any TV that has a screen resolution of 1366 X pixels 768 pixels and is HD Ready will use 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 done by complex software to fill the screen.
When a Full HD signal (1920 x 1080 pixels) is received by a HD Ready TV one to one pixel mapping is not achievable due to insufficient pixels so the picture has to be interpolated to the screen resolution.
‘HD Ready 1080p’ – What is it ?
Any Television that carries the ‘HD ready 1080p’ is naturally capable of displaying a ‘full’ 1080P signal with adequate pixels to offer true pixel-for-pixel mapping without interpolation. A HD ready 1080p flat screen tv has a screen 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 tvs hence the ‘full’ term. These sets will display 1080p and 1080i video without distortion i.e. with 1:1 pixel mapping. They also have HDMI or DVI HD input at 1080p HD and display signals that are at either 24 or 50 frames per second.
If a flat screen 1080P Television receives a 720P picture the signal is ‘oversampled’ to fit the resolution of the 1080P widescreen Television. This is completed using extremely complex algorithm sequences.
Full HD television – What is it ?
Early high definition tv’s didn’t possess the ‘HD Ready 1080p’ logo and may not be compatible with this specification and may not show selected signal inputs.
Interlaced or Progressive
Interlaced picture have two fields that are alternated to produce a frame where every other line is shown 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 displayed one after the other for each frame at two times the frame rate this is known as Interlacing.
One of the benefits of Interlacing is that when footage is shot of a moving image each of the fields of a frame are taken at separate times making motion that appears more fluid. Picture Interlacing is a technique that was first used to improve the image quality of a signal on CRT tvs without using extra signal bandwidth.
In the UK PAL televisions operates at 25 frames a second with 50 fields a second. A broadcasted signal that is Interlaced requires half the signal bandwidth of a Progressive signal. A progressive signal has a scan rate of 50 full frames per second compared with an interlaced signal which has half the frame speed.
Interlaced pictures on recordings made for television or with a video camera aren’t able to be displayed on standard definition LCD televisions and Plasma tvs. This is for the reason that the picture isn’t created with an electron scan like tube televisions so LCD TVs and Plasma TVs don’t benefit from the interlaced picture signal. Flat screen widescreen tv’s have internal processing to produce a progressive scanned picture from a interlaced picture – i.e. Deinterlacing.
Progressive Scanning
This is also known as non-interlaced scanning. It is a method of storing, displaying or transmitting a moving picture where all of the lines of every frame are shown sequentially instead of odd lines in one field and then even lines in the subsequent 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 therefore less eye strain. Also better results are possible for scaling to higher resolutions than the equivalent interlaced sources. For the best scaling results full frames work the best whereas interlaced video sources must be deinterlaced prior to being scaled and this can produce very noticeable combing artifacts.
What is the difference between the 720p/50 and 1080i/25 formats?
On motionless images a 1080i/25 (1920 x 1080 pixels) produces a a little higher horizontal picture resolution than a 720p/50 (1280 x 720 pixels) picture. Moving pictures on an interlaced picture have a lower subjective line resolution because of line twitter or artifacts caused by the fields being somewhat dissimilar that make up a frame. Broadcasters have a tendency to opt for 1080i/25 over 720p/50 as it requires a reduced amount of bandwidth, but both systems are used for HD TV broadcasts.
Smoother movement is created with 720p progressive scanned pictures, above all on slow-motion, compared to 1080i interlaced pictures. Better still pictures are produced with interlaced 1080i signals. With 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 images being predominantly displayed, either static or moving, and your preferences.
When a HD Ready TV 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 obtainable on films with a 1080p signal at 24 frames per second, when viewed via a Blu Ray player on a flat screen high def television. 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 added middle frames so that the frame rate is increased to 48 or 72 producing smoother on screen movement.
Sources of HDTV
HDTV broadcasts are currently at 720p/50 or 1080i/25 and are obtainable on SKY Digital HD, Freesat, BT Vision, and Virgin media Cable. All of these necessitate a HD Ready TV. At this time Full HD 1080P signals are only available on Blu-Ray Disc, Playstation 3 and by download films on the web. The Xbox 360 games machine operates at 720p.
In conclusion
HD enhances the viewing experience and makes TV 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. On the other hand if you need to future proof yourself against the possibility of future full HD 1080p broadcasts then the full HD 1080p models are the ones to buy. Clearly, if you already possess, 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 tv is the sensible choice.
Related posts:
Leave a Reply
You must be logged in to post a comment.