An Introduction to 50hz tv pictures

A standard PAL television will refresh the picture at a frequency of 50Hz or 50 Frames Per Second (FPS). The Frames Per Second are the number of frames needed to create the illusion of movement. On a 50Hz Cathode Ray Television (CRT), because the picture was produced by an electron scan, there was a visible flicker that could be detected by the human eye.

Our eyes are at times are sensitive to this frequency depending on the speed of the image, the level of darkness, and the level of brightness so you will sometimes notice the picture flicker on a 50Hz TV. Also the larger the screen is the more noticeable the flicker is.

How 100 hertz used to work

Originally 100hz (100 FPS) televisions operated at double the Frames Per Second by creating a duplicate of each frame and inserting it after the original one. By doubling the frequency of the scan to 100Hz and inserting a replica frame this effect was eliminated as far the human eye perceives it. The effect of this is to significantly reduce the flicker.

How does 100hz work on LCD and Plasma Tv ?

Plasma and LCD TVs dont have flickering as they dont generate the picture with an electron scan. But LCD TVs are still able to benefit from 100Hz since cpmplex digital circuitry creates a middle image or an extra frame. The TV does this by creating an further frame by means of complex interpolation along with motion compensation calculations to work out what the addition frames and fields look like instead of inserting a copy frame. Therfore the first and second frames are different.

Nevertheless even at 100 Frames Per Second the picture still does not show an absolutely smooth picture especially with fast moving images. Several television producers attempt to reduce this further by using advanced digital picture processing. Typically there is still a little blurring on quick moving images although the benefits are sharper pictures, clearer and better defined surfaces, and smoother movement than is possible from 50 FPS LCD and Plasma TVs.

e.g. For a football that travels ten pixels from left to right between frames one, two and three, the 100 hertz TV will digitally create two further frames between one and two, and two and three, between which the ball will move five pixels. This will result in five frames where the football moves a total of ten pixels i.e. the original frames one, two and three plus the digitally created frames inserted between one and two, and in between two and three. The result of this is that the eye sees an image that moves smoother than before.

The benefits of 100 Hz

100Hz televisions have a clear benefit of eliminating the majority of ghosting effects now and then seen in LCD TVs. The ghosting effect caused by the next image being shown before the previous one has faded away. Plasma television also benefits from 100hz because the extra middle frame smoothes motion on the screen

Manufacturers such as JVC, Panasonic, Samsung, Toshiba, LG, Sony, Philips, Hitachi and Pioneer have got 100 hertz Plasma and LCD televisions.

200hz is even better

A range of 200hz TVs have been produced by Sony which digitally inserts three further frames between the original 50Hz frames. Hence speedy moving sequences are delivered with a more fluid, sharper and smoother picture than 50 hertz or even 100 hertz TVs.

Additional benefit for photosensitive epilepsy sufferers

Scientific studies have proven that for patients with photosensitive epilepsies 100Hz televisions can help prevent seizures when playing video games or watching Tv.