Product Reviews Facts and Notes

HD TV, where the HD is for high definition tv (or high def tvs). This is almost certainly the most important 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 tvs where the resolution is at least 1280×720 pixels or HD Ready. There are 2 types of high def broadcasting, 720p/50 and 1080i/25.

HD Ready - What is it?

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. televisions 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 receive HD inputs by either DVI or HDMI and on Component Inputs.

If a HD Ready television has a screen resolution of 1366 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 TV has to upscale the image (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.

When a Full HD signal (1920 x 1080 pixels) is received by a HD Ready TV one to one pixel mapping is not possible due to insufficient pixels so the image has to be interpolated to the screen resolution.

‘HD Ready 1080p’ - What is it ?

A television that has the ‘HD ready 1080P’ mark is able to show a full 1080p signal because it has sufficient pixels for one to one pixel mapping. This can be done with out Interpolation. The resolution of a 1080p flat screen television is 1920 x 1080 pixels or 1080P. The 1080 signifies the vertical resolution and the P is progressive scan. This is the highest resolution obtainable in the United Kingdom on high definition televisions so hence the term ‘full’. Televisions with this resolution are capable of displaying 1080p and 1080i signals without any distortion and with true pixel for pixel mapping. They must also be equipped with DVI or HDMI inputs for 1080P signals at either 24 or 50 frames per second.

If a flat screen 1080P Television 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.

What is a Full HD TV ?

Early high definition tv’s didn’t possess the ‘HD Ready 1080p’ logo and might not be compatible with this specification and may not display certain signal inputs.

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. Thus 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 successively for each frame at twice the frame rate this is known as Interlacing.

Interlaced images on video have more fluid movement 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.

Interlaced pictures on recordings made for television or with a video camera aren’t able to be displayed on normal definition LCD tvs and Plasma tvs. This is for the reason that the picture isn’t created with an electron scan like CRT televisions so LCD TVs and Plama TVs don’t benefit from the interlaced picture signal. Flat panel widescreen tv’s have internal processing to make a progressive scanned image from a interlaced image - i.e. Deinterlacing.

Progressive scan delivers benefits.

Every frame has all of the lines from the picture on a progressive scanned picture instead of either the even or odd lines as with an interlaced image. Progressive scanning is a means of transmitting, storing and displaying the picture.

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 have got to be deinterlaced before 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 slightly better horizontal resolution on still pictures than a progressive scanned 720p/50 (1,280×720 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.

Smoother movement is produced with 720p progressive scanned pictures, particularly on slow-motion, compared to 1080i interlaced pictures. Better still images 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 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 alter the picture into a 1080i/25 image much easier than a full HDTV can change a 1080i signal into 1080p.

The benefits of a 1080p/24 signal.

The ultimate picture quality is available on films with a 1080p signal at 24 frames per second, when viewed via a BlueRay player on a flat screen high def television. The frame rate of 24 per second is identical to the original cinema film instead of being increased to 25 frames per second. The internal circuitry in the TV produces extra middle frames so that the frame rate is increased to 48 or 72 producing smoother on screen motion.

HDTV Sources

A HD Ready TV can accept all current broadcast formats of 720p/50 or 1080i/25. HD is available 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.

Conclusion

The additional sharpness and vividness of a high definition television 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 HD films off the internet a HD Ready television will be good enough. The only drawback with this is that if any broadcaster decides to begin transmitting in HD in the near future your purchase wont be able to take full advantage of the further screen resolution. Thus if you need to encompass every chance then purchase a full 1080p HD television.