Ampex Corporation

Ampex Systems Corporation

Charles H Coleman

Sidney D Miller

Peter Smidth

A technique is provided for a color imaging system having a luminance component and two color difference (chrominance) components, which allots more space in the compressed data stream to the signal component of greater information content or complexity; that is, which combines the encoding of the components of the data representing a common portion of an image in response to the actual needs of the component, prior to encoding the combined data. To this end, the calculation of the quantizing factors considers the combined information content of both the luminance and chrominance components for the same image location. Thus, low chrominance complexity allows the transmission of more of the luminance information, and vice versa. The system also provides for predetermining the relative complexity of the signal components to thus pre-allot the amount of space for each signal component in the compressed data stream in proportion to its measured complexity.

Method and apparatus for image data compression using combined

Editing of information recovered from a relatively high speed communications medium such as a communications channel or magnetic tape often times allows only a portion of the information to be recovered. Storing information in complete segments from which portions of an image, called 'snatches,' may be recovered helps. An image signal is compressed in such a way that a snatch can be used during decompression to reconstruct a recognizable image from less than all the information that defines the image-thereby giving rise to the notion of a partially reconstructed image. The image information comprises several pixel data blocks with each block including sufficient pixel image data to reconstruct a portion of the image. The pixel data blocks are discrete cosine transformed ('dct') to generate a set of dct coefficient blocks. The dct coefficients for a group of dct coefficient blocks are rank ordered from highest visibility coefficient (corresponding to lowest dct frequency coefficient) to lowest visibility coefficient (corresponding to highest dct frequency coefficient), and then are quantized, entropy encoded, and formatted together with synchronization information and parity checks from the error correction encoding before being transmitted on a channel or recorded on magnetic tape. A decompression and reconstruction arrangement functions essentially as the inverse of the compression arrangement. It is during the decompression that snatches are retrieved and used to reconstruct a partial (video) image by using some but not necessarily all the dct coefficients that define the image.

Ordering and formatting coded image data and reconstructing partial

In a data compression process such as employed to compress video or other data, it is preferable not to compress the image data representative of the video image in a sequential format, or to take the data from the same area of the image. To equalize the information content of the data prior to compression, the present shuffling/deshuffling technique divides the video image into a multitude of image representing blocks, and selects a predetermined number of the image blocks from different spatial locations in the image, to form a succession of data sets representative of the video image information. That is, the selection of the image representing blocks is such that the information content (complexity) in each data set is similar to the information content in each other data set and further similar to the average information content of the entire video image. Thus, the subsequent quantizing factor used in the compression process will tend to be similar for successive data sets, thereby reducing any distortion introduced by the compression process. The image representing blocks may be formed of sequentially scanned blocks of the video image, or of transform coefficients representing similar blocks of the video image. The shuffled data is deshuffled by the inverse process.

Method and apparatus for shuffling image data into statistically

An image data compression technique is described which utilizes calculating means and a selected series of bit calculating stages having delays, to estimate one or more quantization parameters for such data. The estimation process preferably is iterated a number of times, with the values found through each estimation being used as the trial values for subsequent estimations. In addition, an initial trial value is selected by a data look ahead technique, which assures that its value is within range of the final quantization parameter used to quantize the data. The final quantization parameter insures that the compressed data fits within a predetermined number of encoded data bits to be transmitted or recorded, for example, in a recording medium.

Data compression using a feedforward quantization estimator

A method and apparatus are disclosed for eliminating or dropping digital samples from a data stream of samples to reduce the data rate for transmission of the data stream through a transmission channel, such as a data record and reproduce system or the like, and for subsequently reconstructing the original data stream by using the unaltered and recovered digital samples to generate an interpolated value for each of the samples that has been dropped. A finite impulse response multi-term digital filter is used to generate the interpolated value for the samples that have been dropped. Advantages reside in the fact that errors are not propagated during multiple generation recording or transmission, since unaltered sample values are always used to produce the interpolated value for the dropped sample that is being reconstructed. The invention has particular use in video recording and reproducing wherein it is desirable to record a digital data stream at the lowest practicable data rate.

Dropped sample data rate reduction system

A method and apparatus are disclosed for enabling the continuous monitoring of recording circuit performance and the automatic optimization of the recording process in a rotary head recorder having a plurality of recording heads. A calibration signal is recorded by each recording head onto the overlap area of a moving magnetic tape medium. A fixed monitor head subsequently detects components of the recorded signal, the magnitudes of which are squared and retained in sample and hold units. The sampled and held values are periodically used to construct an outputted value commensurate with recording circuit performance. Optimization is accomplished by varying the recording drive level of a recording head about a predetermined point during a series of successive overlap periods. A DC error voltage is derived from the respective outputs resulting from such variation, and used to shift the recording drive level of that head towards a point of optimum playback output.

Record verify and optimize system

A method and apparatus are disclosed for performing a reduction of the data rate of a data stream for transmission through a transmission channel or recording and for subsequently reconstructing the original data stream upon receipt or during reproducing. The method and apparatus utilizes a combination of two processes, one of which eliminates or drops digital samples from the data stream to reduce the data rate for transmission and which subsequently reconstructs the original data stream using the unaltered and recovered digital samples to generate an interpolated value for each of the samples that had been dropped. The second process utilizes differential pulse code modulation for reducing the number of data bits per sample before sending the data stream through the transmission channel and for subsequently restoring the data to its original multi-bit form.

Combined data rate reduction system

A system is described for determining the position of a magnetic read head relative to the center of a selected data track on a magnetic recording medium moving with respect to the read head. Tracking signals of equal frequency, but out of phase a predetermined fixed amount, are recorded on adjacent data tracks. The tracking signal frequency is selected to be a long enough wavelength such that a single read head positioned over a selected data track also detects the tracking signal recorded on adjacent data tracks. A phase comparator compares the phase of the tracking signal detected by the read head with respect to the phase of a reference signal of equal frequency, and a resultant signal is generated which is indicative of any deviation of the read head from the center of the selected track.

Apparatus and method for determining read head position

A magnetic recorder including a playback circuit for decoding a ternary waveform digital data signal is disclosed, wherein positive and negative threshold levels, used to distinguish between signal levels representative of data ones from signal levels representative of data zeros, are automatically adjusted to compensate for occasional reductions in overall signal level that can occur due to dropouts and modulation noise on the magnetic medium. Two sample and hold units are used to generate an output signal whose amplitude reflects only those signal levels that are greater than some minimum absolute value. This output signal is filtered and then used to generate the compensated positive and negative threshold levels.

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Redwood City, CA, United States of America

Charles H Coleman