Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-04-29
2003-02-25
Britton, Howard (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C348S425100, C386S349000
Reexamination Certificate
active
06526100
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for transmitting video images between multimedia terminals in a data transmission system, in which video images are transmitted by using first video frames, in which information encoded from one video image is transmitted, as well as second video frames, in which information encoded on the basis of two or more video images is transmitted, from which a video image can be formed in the receiver multimedia terminal by using at least one first and at least one second video frame. The present invention also relates to a data transmission system, which comprises means for transmitting video images between multimedia terminals, means for forming first and second video frames from the video images, in which first video frames information encoded from one video image is arranged to be transmitted, and in the second video frames information encoded on the basis of two or more video images is arranged to be transmitted. The present invention relates furthermore to a multimedia terminal, which comprises means for receiving commands, and means for generating first and second video frames from video images, in which first video frames information encoded from one video image is arranged to be transmitted, and in the second video frames information encoded on the basis of two or more video images is arranged to be transmitted.
Multimedia applications are used for transmitting e.g. video image information, audio information and data information between a transmitting and receiving multimedia terminal. For data transmission the Internet data network or another communication system, such as a general switched telephone network (GSTN), is used. The transmitting multimedia terminal is, for example, a computer, generally also called a server, of a company providing multimedia services. The data transmission connection between the transmitting and the receiving multimedia terminal is established in the Internet data network via a router. Information transmission can also be duplex, wherein the same multimedia terminal is used both as a transmitting and as a receiving terminal. One such system representing the transmission of multimedia applications is illustrated in the appended FIG.
1
. Definitions for such a multimedia terminal are presented in the International Telecommunication Union ITU-T Recommendation H.324 “Terminal for Low Bit-Rate Multimedia Communication” (Feb. 6, 1998).
The source of information can advantageously be a video application, an audio application, a data application or a combination of these, of which a collective term “multimedia application” is used in this description. In the multimedia application, the user of the multimedia terminal selects the location of the desired source of information, wherein a data transmission connection is established in the system between the selected access location of the information and the multimedia terminal of the user. Data frames, in which the information is transmitted in a digital format, are typically used for transmitting information. A separate data frame is advantageously produced for each different source type, or, in some situations, it is possible to combine data from two or more sources of information into one data frame. In the data transmission system, the data frames are transmitted to the multimedia terminal of the user. In practical applications, these data frames are temporally interlaced, wherein the actual data transmission stream is composed of temporally separated data frames of different applications. There are also systems under development, in which a separate, logical data transmission channel is allocated for different types of applications using, for example, different frequencies or, in CDMA-based systems, different spreading codes. In practice, the data transmission capacity of such data transmission systems is restricted because, for instance, the data transmission channel is physically band restricted and there can be several simultaneous data transmission connections, wherein the entire capacity of the data transmission system cannot be given to the use of any single data transmission connection. In mere audio applications, this does not usually impose a significant drawback, because the amount of information to be transmitted is relatively small. However, in the transmission of video information this restricted bandwidth sets high demands on the data transmission system.
The use of multimedia applications has also been developed in low bit rate data transmission systems, wherein the data transmission rates are in the order of 64 kbit/s, or lower.
The video application can be a TV image, an image generated by a video recorder, a computer animation, etc. One video image consists of pixels which are arranged in horizontal and vertical lines, and the number of which in one image is typically tens of thousands. In addition, the information generated for each pixel contains, for instance, luminance information about the pixel, typically with a resolution of eight bits, and in colour applications also chrominance information, e.g. a chrominance signal. This chrominance signal further consists of two components, Cb and Cr, which are transmitted with a resolution of eight bits. On the basis of these luminance and chrominance values, it is possible at the receiving end to form information corresponding to the original pixel on the display device of the multimedia terminal. In said example, the quantity of data to be transmitted for each pixel is 24 bits uncompressed. Thus, the total amount of information for one image amounts to several megabits. In the transmission of a moving image, several images are transmitted per second, for instance in a TV image, 25 images are transmitted per second. Without compression, the quantity of information to be transmitted would amount to tens of megabits per second. However, for example in the Internet data network, the data transmission rate can be in the order of 64 kbits per second, which makes real time image transmission via this network impossible without the use of compression techniques.
For reducing the amount of information to be transmitted, different compression methods have been developed, such as presented in the ITU-T Recommendation H.263 “Video Coding for Low Bit-Rate Communication”, Geneva 1998. In the transmission of video, image compression can be performed either as interframe compression, intraframe compression, or a combination of these. In interframe compression, the aim is to eliminate redundant information in successive image frames. Typically, images contain a large amount of such non-varying information, for example a motionless background, or slowly changing information, for example when the subject moves slowly. In interframe compression, it is also possible to utilize motion compensation, wherein the aim is to detect such larger elements in the image which are moving, wherein the motion vector of this entity is transmitted instead of transmitting the pixels representing the whole entity. Thus, the direction of the motion and the speed of the subject in question is defined, to establish this motion vector. For compression, the transmitting and the receiving multimedia terminal are required to have such a high processing speed that it is possible to perform compression and decompression in real time.
In several image compression techniques, an image signal converted into digital format is subjected to a discrete cosine transform (DCT) and is subsequently quantised and coded before it is transmitted to a transmission path or stored in a storage means. In this context, the word discrete means that the DCT is calculated using sampled values of cosinusoidal functions, rather than continuous functions.
Using a DCT it is possible to calculate the frequency spectrum of a periodic signal. For example, it is possible to transform the signal from the time domain to the frequency domain. When the discrete cosine transform is applied to a single image, a two dimensional transform is required.
Kalliokulju Juha
Lehtonen Erkko
Britton Howard
Nokia Mobile Phones Limited
Perman & Green LLP
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