Video data transmission

#The present invention relates to video data transmission and is applicable in particular, though not necessarily, to video telephony.

#There are many applications in which the high speed transmission of video data is required. Demand is expected to rise in particular for video telephony services (including video conferencing) over the next few years. With a view to anticipating this expected rise in demand, and also increased demand for other services which require the transmission of video data, the International Telecommunications Union (ITU) is presently laying down new standards in this area. In particular, the Telecommunication Standardisation Sector of ITU (known as ITU-T) has produced a number of draft recommendations, as a precursor to international standards, relating to the point-to-point transmission of video data (and for example available at internet address “ftp://standards.pictel.com”).

#ITU-T recommendation H.324 defines a terminal for low bit rate multimedia communication. H.324 terminals may carry real-time voice, data and video, or any combination thereof and may be integrated into personal computers or implemented in stand-alone devices such as video telephones. The H.324 recommendation incorporates a number of other ITU-T recommendations and is intended to maximise the interworking of terminals which will meet the standard which will result from this recommendation.

#For a better understanding of the present invention and in order to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings, in which:

#FIG. 1 shows schematically a video data transmission system in which only a luminance component of a video signal is encoded and transmitted;

#FIG. 2 shows schematically a video data transmission system in which chrominance components of a video signal are provided to an encoder where they are encoded as null signals for transmission with a luminance component; and

#A video transmission system is illustrated in FIG. 1 and comprises a transmission terminal 1, a data transmission channel 2, and a reception terminal 3. Both the transmission and reception terminals conform generally to the ITU-T recommendation H.263 whilst the transmission channel may be a wireless channel, a coaxial cable, a fibre optic cable, or any other suitable means.

#The transmission terminal 1 has a colour video camera 4 which generates a video signal comprising luminance (Y) and chrominance (U,V) components in accordance with recommendation H.263. As will be known to the skilled person, the luminance component (Y) contains the tone information of a video image, i.e. the amount of black and white in the image, whilst the chrominance components (U,V) contain the colour information. The transmission terminal 1 also comprises an encoder 5 which is capable of encoding the luminance and chrominance signals generated by the colour video camera 4 into a form suitable for transmission via the transmission channel 2. Encoding involves compressing the video signals to reduce the transmission bit-rate.

#The reception terminal 3 comprises a video decoder 6 which receives the encoded video information transmitted over the transmission channel 2 and decodes this information into separate chrominance and luminance components for transmission to a video display 7.