High Definition Television or HDTV is the main change to
broadcasting and television since the introduction of colour. Flat
screen lcd televisions and plasma televisions with a minimum screen
resolution of 1280 pixels x 720 pixels are known as HD Ready and are
able of displaying current HD broadcasts.
What does 'HD ready' mean ?
Any television that is HD Ready is capable of receiving and displaying
a HD picture. To meet this specification the television should have a
picture resolution of at least 1280 pixels x 720 pixels. They have to
be able to accept a signal that is 1080i/25 or 720p/50, where the 1080
or 720 is the number of vertical lines, the 'i' is for an interlaced
picture and the 'p' is for a progressive scan picture, and the 25 and
the 50 are the number of frames displayed each second. Additionally the
televisions must have either DVI or HDMI and Component signal input
connectors.
For a 1366 x 768 pixels HD ready tv, if it receives a 1080i signal then
scalers within the flat screen tv will down convert the image to fit
the 768 lines flat screen tv. This is done using complex algorithm
sequences in the scaler which systematically crops the image down to
the resolution of the screen. If the signal is at 720p then the signal
will be slightly upscaled to fill the 768 vertical lines using
complicated algorithms.
Most HD ready tvs don't have sufficient pixels to offer true
pixel-for-pixel mapping without interpolation of the higher HD
resolution (1920 x 1080 pixels).
What does 'HD ready 1080P' mean ?
If a plasma television or lcd television has a 'HD ready 1080p' badge
it has enough pixels to show the full 1080p signal with pixel for pixel
mapping with no interpolation. A 1080p flat panel lcd television or
plasma tv is 1920 X pixels 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 maximum picture
resolution in the UK for high definition and therefore 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 TVs must be able to display a 1080p/24 or 1080p/50
signal where the 24 and the 50 correspond to the number of frames per
second.
If a flat panel 1080P TV receives a 720P picture the signal is
'oversampled' to match the resolution of the 1080P widescreen
Television. This is done using extremely complex algorithm sequences.
Full HD
Older full HD flat panel tv's may possibly not fulfill all 'HD Ready 1080P' requirements.
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 contains the odd lines and the other
field includes the even lines. Interlacing is when these two fields are
shown in sequence at double the rate of the actual frame and at half
the resolution.
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.
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.
Standard definition LCD tvs and Plasma televisions 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.
Progressive Scanning
This is a method to display, transmit, and store a moving picture.
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.
The advantages of Progressive Scanning is that there is a greater
vertical resolution than on Interlaced pictures at the same frame rate
with no blurring, interlace artifacts, and reduced eye strain. It is
also viable to scale to a higher resolution than it is with comparable
interlaced sources. Because interlaced signal sources have to be
deinterlaced before scaling with observable combing artifacts,
Progressive scanned full pictures give the best results when scaling.
The differences between 720p/50 and 1080i/25 formats
When a 1080i/25 (1,920 pixels x 1080 pixels resolution) signal displays
a still image the horizontal resolution is marginally better than the
720p/50 (1,280 x 720 pixels resolution) image. When an picture moves on
an interlaced signal the subjective line resolution is reduced due to
line twitter since the two fields that make up the frames are a little
different. Depending on the bandwidth availability broadcasters are at
present using either 720p/50 or 1080i/25.
Smoother movement is produced with 720p progressive scanned images,
above all on slow-motion, compared to 1080i interlaced images. 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 ought to choose,
will depend on the type of images being predominantly displayed, either
static or moving, and your preferences.
When a HD Ready television receives a 1080p/50 signal it can alter the
image into a 1080i/25 picture much easier than a full HDTV can change a
1080i signal into 1080p.
What is 1080p/24 ?
Because the films that are shown in cinemas are produced at 24 frames
per second a signal is in its uncorrupted form at this frame rate.
Films are obtainable on Blueray disc at 24 frames per second that give
the ultimate picture quality when displayed on widescreen full high def
tv's. When a full hd tv receives a 1080p/24 signal it creates
additional middle frames, which are inserted between the original ones
to raise the frame rate to 48 or 72 frames per second giving more fluid
motion.
Sources of HDTV
A HD Ready TV can receive 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
Blueray players, Playstation 3 and by download on the internet. The
games on an Xbox 360 are at 720P.
In conclusion
The additional sharpness and vividness of a high definition TV picture
enhances the viewing experience. Unless you have, or expect to purchase
a Blueray player, Playstation 3 or you are going to down load 1080p
high definition films off the web a HD Ready television will be good
enough. The only problem with this is that if any broadcaster decides
to commence transmitting in HD in the near future your purchase won't be
able to take complete advantage of the further screen resolution. Thus
if you would like to cover every possibility then buy a full 1080p HD
television.
Before you purchase any electrical products online, make sure
you goto Armadeus Cornelius' excellent website for additional
information on
HD TV, and also
Discount Flat Screen TVs
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