Motion picture compression technique used in digital television sets

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[...] Using Motion Picture compression technique like MPEG, the difference picture is produced by subtracting every pixel in one picture from the same pixel in the next picture. MPEG-1 and MPEG-2 standards are similar in basic concepts. They both are based on motion compensated block based transform coding techniques, while MPEG-4 deviates from these more traditional approaches in its usage of software image construct descriptors, for target bit-rate in the very low range REFERENCES http://www.nab.org/ http://www.dvb.org/ Digital Television News http://www.qt3.com/newstrek/index Figure- Set-Top-Box with Conditional Access System Introduction The development of digital Television and interactive services is already underway in various locations around the globe. [...]

[...] MPEG-2 It was finalized in 1994, and addressed issues directly related to digital television broadcasting such as the efficient coding of field- interlaced video and scalability. Also the target Bit rate was raised between 4 and 9 Mb/sec, resulting in potentially very high quality video. MPEG-2 consists of profiles and level. The profile defines the bit stream scalability and the colour space resolution, while the level defines the image resolution and maximum bit-rate per profile. Probably the most common descriptor in use currently is Main Profile, Main Level (MP@ML)which refers to 720 x 480 resolution video at 30 frames/sec, at bit-rate up to 15Mb/sec for NTSC video. [...]

[...] MPEG compression dramatically decreases the amount storage space required to record motion picture sequences by eliminating redundant and non essential image information from the stored data. Less total bits means that motion pictures can be transferred more rapidly, so rapidly in fact, that slow, but inexpensive, communication line and storage devices have entirely new moving picture applications. The human eye is forgiving of approximation and outright elimination of the finest details in images. This is fortunate because there is proportionally a lot more fine detail than coarse detail in images. [...]

[...] If digital technique is to be used for Television system the composite video signal must be digitized i.e. a binary sequence of 0's and 1's must be used. Digital television uses the same language as computers- a long stream of binary digits, each of which is either 0 or 1. With digital television the signal is compressed and only the updated data transmitted. As a result, it is possible to squeeze 6 or 8 channels into frequency range that was previously occupied by only one analog Television channel. [...]

[...] Compression schemes designed for still images, such as JPEG (Joint Photographic Experts Group) have to work in this way. For moving pictures, exploiting redundancy between pictures, known as inter-coding, gives a higher compression factor. Following Figure shows a simple inter-coder. Starting with an intra-coded picture, the subsequent pictures are described only by the way in which they differ from the one before. The decoder adds the differences to the previous picture to produce the new one. The difference picture is produced by subtracting every pixel in one picture from the same pixel in the next picture. [...]