Abstract: A post-processor for a decoded video sequence includes a digital noise reduction unit and an artifact reduction unit which significantly reduce blocking artifacts and mosquito noise in a video image. The post-processor uses both temporal and edge characteristics of the video image to enhance the displayed image. A coding parameter from a decoder is used in a coding parameter adaptive filter unit within an artifact unit to further enhance the perceived quality of the displayed image. The coding parameter for a particular macroblock is selected using a characteristic of that macroblock. The post-processor operates on a current frame of pixel data using information from the immediately preceding post-processed frame that is stored in a frame memory of the post-processor. The post-processor uses artifact reduction only on portions of the image that are not part of an edge, and are not part of a texture or fine detail area.

Abstract: A post-processor for a decoded video sequence includes a digital noise reduction unit and an artifact reduction unit which significantly reduce blocking artifacts and mosquito noise in a video image. The post-processor uses both temporal and edge characteristics of the video image to enhance the displayed image. The post-processor operates on a current frame of pixel data using information from the immediately preceding post-processed frame that is stored in a frame memory of the post-processor. The post-processor first identifies texture and fine detail areas in the image. The post-processor uses artifact reduction only on portions of the image that are not part of an edge, and are not part of a texture or fine detail area. Since artifact reduction is not utilized on these areas, the post-processed image is not softened in regions where it is easily noticed by the human eye.

Abstract: A statistical multiplexer selectively passes packets of encoded data from a plurality of encoders to a communication channel so as to maximize the quality of the encoded data. The statistical multiplexer determines what fraction of the communication channel capacity should be allocated to an application so as to optimize the quality of the decoded signals of the applications processed by the statistical multiplexer. A table is stored in a memory of the statistical multiplexer that has an entry for each unit of encoded data that can be transmitted over the communication channel in a predetermined time interval. The statistical multiplexer accesses each entry in the table to obtain a pointer, e.g., an address, to an encoder that can transmit the next unit of encoded data to the communication channel.

Abstract: A low bandwidth video teleconferencing system and method is disclosed. The video teleconferencing system employs novel data compression techniques by which continuous transmission of imagery at a rate of 9600 bits/second is possible. A sketch coder converts the grey scale image to be transmitted to a sketch or line drawing, which comprises an outline of the principal boundaries plus shading to represent depth. The bandwidth required for the data representing the sketch is then compressed by two-dimensional run length coding techniques which exploit interframe and interline redundancy as well as intraline redundancy to generate a binary transmission code. Other features are also provided.

Abstract: An apparatus and method for signal processing employing intraframe and interframe variable prediction transform coding. Images are represented by sequential frames of two-dimensional arrays of digital signals. The digital signals are transformed to form transform coefficients for each frame. Predicted transform coefficients are formed using sets of variable prediction factors. The predicted transform coefficients for each frame are compared with corresponding actual transform coefficients for the frame to form transform coefficient difference signals. The difference signals are processed to control their range of values. The processed difference signals are statistically coded such that the more frequently occurring values are represented by shorter code lengths and the less frequently occurring values are represented by longer code lengths. The coded signals are stored in a buffer memory for transmission.

Abstract: The present invention relates to methods and apparatus for processing signals to remove redundant information thereby making the signals more suitable for transfer through a limited-bandwidth medium. The present invention specifically relates to methods and apparatus useful in video compression systems. Typically, the system determines differences between the current input signals and the previous input signals using mean-square difference signals. These mean-square signals are processed and compared with one or more thresholds for determining one of several modes of operation. After processing in some mode, the processed signals are in the form of digital numbers and these digital numbers are coded, using ordered redundancy coding, and transmitted to a receiver.

Abstract: Video type information signals are compressed for transmission and reproduction by comparing corresponding blocks of time domain information signals from successive fields, converting a block of the time domain information signals to a transform domain signal represented by discrete cosine transform coefficients when the difference between the corresponding blocks exceeds a block difference threshold, and encoding the transform domain coefficients for transmission to a decoding site. Corresponding blocks of time domain information signals from successive fields are compared by storing the successive fields in memory on a pixel by pixel basis, retrieving each block on a pixel by pixel basis, forming the difference between corresponding pixels from the successive blocks, squaring the resulting difference signal, summing the squares and dividing by the number of pixels per block. Successive fields are merged by weighted summing of corresponding pixels.

Abstract: A dual mode facsimile data compression technique which possesses the advantage of symbol recognition and extended run-length coding methods. In operation, a symbol blocking operator isolates digital raster data representing valid alphanumeric characters and document symbols. The first symbol encoungered is placed in a memory or library and as each new symbol is detected, it is compared with each entry of the library. If the comparison is within a predetermined tolerance, a library identification code representing the symbol is generated and transmitted along with the symbol location coordinates. Otherwise, the new symbol is placed in the library and its digital pattern and location is transmitted. A scoring system determines which elements of the library are to be replaced by new prototypes once the library is filled. Non-isolated symbols are coded by a two-dimensional run-length coding method for transmission.

Abstract: A digital video compression and expansion system and its methods for compressing and expanding digitalized video signals in real time at rates up to NTSC color broadcast rates are disclosed. The system compressor receives digitalized video frames divided into subframes, performs in a single pass a spatial domain to transform domain transformation in two dimensions of the picture elements of each subframe, normalizes the resultant coefficients by a normalization factor having a predetermined compression ratio component and an adaptive rate buffer capacity control feedback component, to provide compression, encodes the coefficients with a minimum redundancy coding scheme and stores them in a first rate buffer memory asynchronously at a high data transfer rate from which they are put out at a slower, synchronous rate.

Abstract: An improved method and apparatus for calculating discrete cosine transform coefficients from a plurality of digitalized data is disclosed. The pipelined processor utilizes two basic types of circuits arranged in five computational stages. Shuffle and add circuits operate upon prearranged data components at the first, second and fourth stages, while shuffle, add and multiply circuits are used at the third and fifth stages.

Abstract: A digital video compression system and its methods for compressing digitalized video signals in real time at rates up to NTSC color broadcast rates are disclosed. The system compressor receives digitalized video frames divided into subframes, performs in a single pass a spatial domain to transform domain transformation in two dimensions of the picture elements of each subframe, normalizes the resultant coefficients by a normalization factor having a predetermined compression ratio component and an adaptive rate buffer capacity control feedback component, to provide compression, encodes the coefficients and stores them in a first rate buffer memory asynchronously at a high data transfer rate from which they are put out at a slower, synchronous rate.

Abstract: A high speed character matcher and method for measuring the similarity between a pair of binary patterns representing two-dimensional images. The patterns are compared on a bit by bit basis and when a discrepancy is detected, it is assigned an error penalty which is based on the two-dimensional context in which the error occurred. The types of error context which are typical in the comparison of distorted but otherwise similar characters are given a lower error than those typically encountered in the comparison of dissimilar characters.

Abstract: Disclosed herein is a data compression system for compressing binary facsimile data to reduce transmission times over standard telephone system circuits. At the transmit end of the circuit a segment of adjacent scans of, e.g., a white or light background document having, e.g., black typewritten characters or other symbols thereon is stored in a binary format in a buffer memory. A scanner scans the memory to locate the position of a beginning point of each individual character. A block definer circuit then defines a rectangular block closely enclosing the character. A block mapping circuit then scans the block following a predetermined pattern and provides a binary sequence of the black and white portions thereof. A run length encoder may then encode the binary sequence by run length or by Huffman code. A modem connected to the telephone lines sends data corresponding to the location, size and contents of each character block to a receiving modem at the receive end of the telephone circuit.