What is HD Ready and HD TV ?

What is HDTV ?

HD TV, where the HD is for high definition television (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 televisions such as a Plasma televisions and LCD tv's where the screen resolution is at least 1280 pixels x 720 pixels or HD Ready. There are 2 types of high def broadcasting, 720p/50 and 1080i/25.

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 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 image 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.

For a 1366 pixels x 768 pixels HD ready TV, if it receives a 1080i signal then scalers within the flat panel tv will down convert the image to fit the 768 lines on a flat screen television. 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 televisions don't have enough pixels to give true pixel-for-pixel mapping without interpolation of the higher HD resolution (1920 pixels x 1080 pixels).

What does ‘HD ready 1080P’ mean ?

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 screen tv has a picture resolution of (1920 pixels x1080 pixels) i.e. 1080P, where ‘1080’ is the vertical resolution of the picture 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 video 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.

If a flat screen 1080P TV receives a 720P picture the signal is ‘oversampled’ to fit the resolution of the 1080P widescreen TV. This is completed using extremely complex algorithm sequences.

Full HD

Older full HD flat panel tv’s may not fulfill all ‘HD Ready 1080P’ requirements.

Interlaced or Progressive

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 every field has half the resolution. The two fields of the frame are alternately displayed in sequence at a rate that is double 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 movements that appears more fluid. Picture Interlacing is a procedure that was originally used to improve the image quality of a signal on CRT tvs without using extra signal bandwidth.

TVs 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 has to scan the picture 50 times per second whilst the interlaced scanning process operates at half of that speed.

Standard definition LCD televisions 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 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 rather than odd lines in one field and then even lines in the subsequent field as per Interlaced signals.

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 best 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.

What is the difference between the 720p/50 and 1080i/25 formats?

A 1080i/25 (1,920x1080 pixel resolution) interlaced signal has to some extent better horizontal resolution on still pictures than a progressive scanned 720p/50 (1,280x720 pixel resolution) image. 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.

Progressive scanning 720p gives more fluid motion, especially on slow-motion, than an interlaced 1080i signal. But interlaced 1080i signals give better static resolution. If the internal processing is good enough a 1080i signal on a 1080 display will still look better than the 720p material. The best one depends on whether you are to display more static pictures or more moving pictures and what is more critical to you.

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 is 1080p/24 ?

This is 1080p at 24 frames per second. This gives the greatest picture quality with the 1080p picture decoded directly from the BlueRay disc at 24 frames per second, and then sent to the flat screen HD TV. The 24 frames per second is the same rate as the original cinema film. The Television will then create additional frames to multiply to either 48 or 72 frames per second creating middle frames that make the picture more fluid.

Sources of HDTV

HDTV broadcasts are presently at 720p/50 or 1080i/25 and are available on SKY Digital HD, Freesat, BT Vision, and Virgin media Cable. All of these require a HD Ready TV. At this time Full HD 1080P signals are only obtainable on Blue-Ray Disc, Playstation 3 and by download films on the web. The Xbox 360 games machine operates at 720p.

Conclusion

The additional sharpness and vividness of a high definition television picture enhances the viewing experience. Unless you own, or intend to purchase a Blueray player, Playstation 3 or you are going to down load 1080p HD films off the internet a HD Ready TV will be good enough. The only drawback with this is that if any broadcaster decides to start transmitting in high definition in the near future your purchase wont be able to take full advantage of the added screen resolution. Thus if you want to cover every chance then purchase a full 1080p HD television.

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