EP0460188A1 - High speed compression of imagery data - Google Patents

High speed compression of imagery data

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Publication number
EP0460188A1
EP0460188A1 EP19910902065 EP91902065A EP0460188A1 EP 0460188 A1 EP0460188 A1 EP 0460188A1 EP 19910902065 EP19910902065 EP 19910902065 EP 91902065 A EP91902065 A EP 91902065A EP 0460188 A1 EP0460188 A1 EP 0460188A1
Authority
EP
European Patent Office
Prior art keywords
data
compression
signals
sub
data signals
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19910902065
Other languages
German (de)
French (fr)
Inventor
David William Dellert
Frank Weiner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Eastman Kodak Co
Original Assignee
Eastman Kodak Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eastman Kodak Co filed Critical Eastman Kodak Co
Publication of EP0460188A1 publication Critical patent/EP0460188A1/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/41—Bandwidth or redundancy reduction
    • H04N1/411—Bandwidth or redundancy reduction for the transmission or storage or reproduction of two-tone pictures, e.g. black and white pictures
    • H04N1/413—Systems or arrangements allowing the picture to be reproduced without loss or modification of picture-information
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/42—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation
    • H04N19/436—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation using parallelised computational arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/30—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using hierarchical techniques, e.g. scalability

Definitions

  • the present invention relates in general to imagery signal processing and is particularly directed to a system for executing high speed compression of imagery data, particularly alpha-numeric text, by parallel processing of subsampled pixel data, so as to facilitate high speed data communication of the imagery data over a digital communication link, such as that employed for facsimile communication and image reconstruction.
  • Such compression units customarily use some form of one or two-dimensional Huffman encoding mechanism that has been optimized to compress the text- representative data 'across the page 1 and typically operate at a signal processing rate of up to five megabits per second, and more commonly on the order of one to two megabits per second.
  • conventional, mass market facsimile systems regardless of the input data rate, are capable of achieving a document processing rate of only about one page per minute.
  • a high data rate e.g.
  • optical scanner may be used to convert the printed text to digital data, because of the slow processing speed of the compression chip, it is necessary to buffer the input data until it can be accessed at the slower rate of the compression mechanism, thus increasing system cost without an improvement in document processing speed.
  • the signal processing system rather than directly compress successive data samples in the order they are supplied in an 'across the page', line by line format, the signal processing system according to the present invention subdivides or subsamples the data into respective sub-arrays of pixel data, the rate of occurrence of successive ones of which is lower than the original data, particularly at a rate of occurrence which is processing speed- compatible with the compression speed of readily available compression chips. These subsample arrays of data are then coupled to respective lower speed compression units to effect a parallel compression of the subsampled data.
  • the data rate of successive data values within the subsampled arrays is only a fraction of the rate at which successive data values are supplied by the optical scanning device, it is possible to make use of the above-mentioned, low cost compression units to perform the compression operation.
  • the number of compression units required will depend upon the intended data rate and the compression rate of an individual compression chip. As pointed out previously, readily available, low cost chips can typically handle data rates on the order of one to five megabits. Consequently, for a ten to twelve megabits per second communication channel the number of compression chips required will be on the order of two to ten. However, such chips are considerably less expensive than the cost of memory units that would be necessary in the course of compressing the bit map data at the high input data rates.
  • the compressed subsampled data is then combined for transmission over a high data rate communication channel to a receiver site.
  • successive portions of the compressed signals that have been transmitted over the communication channel from the transmitter site are coupled to respective ones of a plurality of parallel data decompression units, which produce decompressed output signals.
  • the decompressed output signals produced by the decompression units are coupled to a parallel-serial shift register. By serially reading out the contents of the shift register, there is obtained a reconstructed serial data stream representative of the multi-dimensional array of imagery data sample values.
  • the direction in which the data is most high correlated is generally orthogonal to the that in which the text is optically scanned (across the page) .
  • the shapes of typed or printed text tend to have a significant component in the vertical or down-the-page direction, rather than in the horizontal direction, so that successive samples of an image of a page (multiple lines) of text will usually undergo fewer transitions (e.g. dark to light) in the vertical direction than in the horizontal direction.
  • transitions e.g. dark to light
  • signals representative of a multi-dimensional array of imagery data sample values for transmission over a communication channel at a prescribed data rate are compressed by providing a plurality of data compression units, a respective one of which is capable of compressing data supplied to it at a compression rate (e.g. one to five Mb/s) that is a fraction of the transmission data rate (e.g. 10 - 12 Mb/s) .
  • a compression rate e.g. one to five Mb/s
  • a fraction of the transmission data rate e.g. 10 - 12 Mb/s
  • bit map respective pixel locations of which are associated with the signals to be transmitted, is then subsampled or subdivided by demultiplexing the successive data (pixel) values of the successive rows of the map into a plurality of sub-arrays of data successive ones of which correspond to every kth data value of the original map.
  • the data values of the sub-arrays are then coupled to respective sets of compression units, each of which is associated with a respective sub-array and is of the type which is capable of executing two- dimensional compression of its input data.
  • FIG. 1 is a block diagram of an embodiment of an imagery data communication system which employs the improved compression mechanism in accordance with the present invention;
  • Figures 2 and 3 show respective sub-arrays of bit map data demultiplexed by the system of Figure 1;
  • FIG. 4 shows an enlarged section of text.
  • FIG. 1 a block diagram of an embodiment of an imagery data communication system which employs the improved compression mechanism in accordance with the present invention is illustrated as comprising a transmitter site 10 having an imagery data source 11 (e.g. an opto-electronic document scanner which is arranged to effect raster type scan of a document, such as successively fed pages of printed text) , data source 11 producing a series of digitally encoded signals respectively representative of successively sampled grey level values of the (text) image.
  • imagery data source 11 e.g. an opto-electronic document scanner which is arranged to effect raster type scan of a document, such as successively fed pages of printed text
  • data source 11 producing a series of digitally encoded signals respectively representative of successively sampled grey level values of the (text) image.
  • each of the encoded signal values corresponds to a respective pixel location in a bit nap 13 of the scanned image, the bit map effectively comprising a two-dimensional array of pixel data, M (e.g. 1768) columns wide by N (e.g. 2200) rows deep.
  • M e.g. 1768
  • N e.g. 2200
  • this limitation in document processing speed of conventional facsimile transmission systems is dramatically increased by effectively subsampling or subdividing bit nap 13 into a plurality of sub-arrays of data, successive ones of the data contents of the sub-arrays corresponding to every kth data value of the original nap.
  • the original imagery data bit map is coupled to a demultiplexer ' 15, K respective output ports 17-1...17- ⁇ of which are coupled to a plurality of data compression units 21-1...21-K, each of which is capable of carrying out two-dimensional compression on the sub-array of data applied to it.
  • a respective one of compression units 21-1...21-K may be a readily commercially available unit, commonly employed in mass market facsimile equipment and capable of compressing data supplied to it at a compression rate (e.g. one to five Mb/s) that is a fraction of the transmission data rate (e.g. 10 - 12 Mb/s) from imagery data source 11.
  • a compression rate e.g. one to five Mb/s
  • a fraction of the transmission data rate e.g. 10 - 12 Mb/s
  • demultiplexer 15 subdivides bit map 13 into K sub-arrays of pixel data.
  • K the sub-divided bit map may be demultiplexed into a pair of respective sub-arrays 31 and 32, as diagrammatically illustrated in Figures 2 and 3," respectively.
  • the image represented by the pixel data is a typical document transmitted by facsimile, such as a page of alpha numeric characters
  • there is a substantial inherent high correlation property among successive data samples due to the 'elongated' nature of the text, in the vertical or 'down the page' direction, as exemplified by portions of alpha numeric characters lying along line L in the enlarged section of text shown in Figure 4. Consequently, even though, for respective rows of the bit map 13, the data subsamples of sub-arrays 31 and 32 are non-consecutive (e.g. pixel values PO,0, PO,2, P0,4, P0,6....
  • each compression unit 21 suffers no loss in output signal quality.
  • the compressed output signals from compression units 21 are coupled to an output multiplexer 25 to be combined for high data rate transmission (e.g.
  • a receiver modem 42 outputs the compressed data signals that have been transmitted over communication channel 40 from transmitter site 10 to a demultiplexer 44, which, under the control of a receiver site microcontroller 43, controllably separates the incoming compressed data stream into respective output segments for application, via output ports 44-1...44-K, to a plurality of data decompression units 46-1...46-K.
  • each of decompression units 46-1...46-K may be a readily commercially available unit, commonly employed in mass market facsimile equipment and capable of effecting a two-dimensional decompression of data supplied to it at a compression rate (e.g. one to five Mb/s that is a fraction of the transmission data rate (e.g. 10 - 12 Mb/s) over channel 40.
  • a compression rate e.g. one to five Mb/s that is a fraction of the transmission data rate (e.g. 10 - 12 Mb/s) over channel 40.
  • the decompressed output signals produced by the decompression units 46 are coupled to parallel input ports 52-1...52-K of a parallel-serial shift register 55. As the contents of shift register 55 are serially read out over serial output data, there is obtained a reconstructed serial data stream representative of the original bit map of imagery data sample values.
  • shift register 55 As will be appreciated from the foregoing description, by subsampling high data rate imagery data into respective sub-arrays prior to data compression, ' it is possible to employ low cost readily available compression units whose processing speed is considerably less than the transmission data rate.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Computing Systems (AREA)
  • Theoretical Computer Science (AREA)
  • Compression Of Band Width Or Redundancy In Fax (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)

Abstract

Un système de traitement d'une topographie binaire de signaux de données d'éléments d'image représentatifs d'un réseau multidimensionnel de données d'imagerie (par exemple un texte alpha-numérique) pour la transmission par un canal de communication de facsimilé permet de comprimer des données d'imagerie à l'aide de plusieurs unités de compression de données, dont une unité respective est capable de comprimer des données qui sont envoyées à une vitesse de compression qui n'est qu'une fraction de la vitesse des données. La topographie binaire est sous-échantillonnée en la démultiplexant en sous-réseaux de données. Les données des sous-réseaux sont couplées sur des ensembles respectifs des unités de compression qui exécutent une compression parallèle et bi-dimensionnelle des données des sous-réseaux démultiplexées. Même si les sous-échantillons de données associés aux rangées successives de la topographie binaire ne sont pas consécutifs, et que par conséquent ils peuvent contribuer à une réduction de l'opération de compression dans le sens horizontal compte tenu du fait que les données sont du texte, des échantillons de données successifs à l'intérieur de chaque colonne d'un sous-réseau sont en corrélation inhérente à un degré plus élevé entre eux que les valeurs de données que l'on rencontre à l'intérieur des rangées respectives de l'acquisition des bits d'origine. En conséquence, l'opération de compression de données bidimensionnelles executée par chaque unité ne souffre d'aucune baisse de qualité du signal de sortie.A system for processing a binary topography of data signals of picture elements representative of a multidimensional network of imagery data (for example an alpha-numeric text) for transmission by a facsimile communication channel allows compress imaging data using multiple data compression units, one of which is capable of compressing data that is sent at a compression rate that is only a fraction of the data speed . Binary topography is subsampled by demultiplexing it into data subnets. The data of the sub-networks is coupled on respective sets of the compression units which perform parallel and two-dimensional compression of the data of the demultiplexed sub-networks. Even if the sub-samples of data associated with the successive rows of the binary topography are not consecutive, and that consequently they can contribute to a reduction of the compression operation in the horizontal direction taking into account that the data are text, successive samples of data within each column of a subnet are inherently correlated to a greater degree than the data values encountered within the respective rows of the acquisition of the original bits. Consequently, the two-dimensional data compression operation performed by each unit suffers from no reduction in the quality of the output signal.

Description

HIGH SPEED COMPRESSION OF IMAGERY DATA
FIELD OF THE INVENTION
The present invention relates in general to imagery signal processing and is particularly directed to a system for executing high speed compression of imagery data, particularly alpha-numeric text, by parallel processing of subsampled pixel data, so as to facilitate high speed data communication of the imagery data over a digital communication link, such as that employed for facsimile communication and image reconstruction.
BACKGROUND OF THE INVENTION Because currently manufactured facsimile systems use relatively low cost signal processing components that are available from a wide variety of chip suppliers, it has been possible to keep the price of individual transceiver units reasonably low, so that the facsimile equipment market presently enjoys mass appeal. One of the major components that governs the cost of the system is the compression unit through which signals (output from an optical scanner) , representative of the contents of a document, are compressed and formatted for transmission to a remote terminal unit. Such compression units customarily use some form of one or two-dimensional Huffman encoding mechanism that has been optimized to compress the text- representative data 'across the page1 and typically operate at a signal processing rate of up to five megabits per second, and more commonly on the order of one to two megabits per second. As a result, conventional, mass market facsimile systems, regardless of the input data rate, are capable of achieving a document processing rate of only about one page per minute. In this regard, even though a high data rate (e.g. 10 - 12 Mb/s) optical scanner may be used to convert the printed text to digital data, because of the slow processing speed of the compression chip, it is necessary to buffer the input data until it can be accessed at the slower rate of the compression mechanism, thus increasing system cost without an improvement in document processing speed.
SUMMARY OF THE INVENTION In accordance with the present invention, this limitation in document processing speed of conventional facsimile transmission systems is dramatically increased without the need for extra storage capability (intermediate buffering) or the additional cost of computationally complex compression modules, so that document processing speeds in excess of at least an order of magnitude greater than conventional units may be achieved. To this end; rather than directly compress successive data samples in the order they are supplied in an 'across the page', line by line format, the signal processing system according to the present invention subdivides or subsamples the data into respective sub-arrays of pixel data, the rate of occurrence of successive ones of which is lower than the original data, particularly at a rate of occurrence which is processing speed- compatible with the compression speed of readily available compression chips. These subsample arrays of data are then coupled to respective lower speed compression units to effect a parallel compression of the subsampled data.
Namely, because the data rate of successive data values within the subsampled arrays is only a fraction of the rate at which successive data values are supplied by the optical scanning device, it is possible to make use of the above-mentioned, low cost compression units to perform the compression operation. The number of compression units required will depend upon the intended data rate and the compression rate of an individual compression chip. As pointed out previously, readily available, low cost chips can typically handle data rates on the order of one to five megabits. Consequently, for a ten to twelve megabits per second communication channel the number of compression chips required will be on the order of two to ten. However, such chips are considerably less expensive than the cost of memory units that would be necessary in the course of compressing the bit map data at the high input data rates. The compressed subsampled data is then combined for transmission over a high data rate communication channel to a receiver site.
At the receiver site, successive portions of the compressed signals that have been transmitted over the communication channel from the transmitter site are coupled to respective ones of a plurality of parallel data decompression units, which produce decompressed output signals. The decompressed output signals produced by the decompression units are coupled to a parallel-serial shift register. By serially reading out the contents of the shift register, there is obtained a reconstructed serial data stream representative of the multi-dimensional array of imagery data sample values.
Now although subsampling the data into sub- arrays tends to reduce the correlation properties of the data (since successive samples of a sub-array occur only every kth data value or pixel of the original imagery data or bit) , and thus implies a reduction in compression performance, according to the present invention, this minor reduction in the correlation properties of data subsamples in the 'across the page' or horizontal direction of the bit map is offset by ' taking advantage of an inherent correlation property of the type of data (e.g text) most frequently transmitted by facsimile equipment and parallel-compressing the data 'down the page' .
More particularly, for normal alpha-numeric text and business, personal computer-generated graphics, the direction in which the data is most high correlated is generally orthogonal to the that in which the text is optically scanned (across the page) . The shapes of typed or printed text tend to have a significant component in the vertical or down-the-page direction, rather than in the horizontal direction, so that successive samples of an image of a page (multiple lines) of text will usually undergo fewer transitions (e.g. dark to light) in the vertical direction than in the horizontal direction. As a result, what each of the parallel compression units sees is a more highly correlated signal stream than would be encountered if the data were supplied to the compression units from a horizontal or row-direction readout of the bit map. In accordance with a preferred embodiment of the present invention, signals representative of a multi-dimensional array of imagery data sample values (e.g. alpha-numeric text) for transmission over a communication channel at a prescribed data rate are compressed by providing a plurality of data compression units, a respective one of which is capable of compressing data supplied to it at a compression rate (e.g. one to five Mb/s) that is a fraction of the transmission data rate (e.g. 10 - 12 Mb/s) . The bit map, respective pixel locations of which are associated with the signals to be transmitted, is then subsampled or subdivided by demultiplexing the successive data (pixel) values of the successive rows of the map into a plurality of sub-arrays of data successive ones of which correspond to every kth data value of the original map. The data values of the sub-arrays are then coupled to respective sets of compression units, each of which is associated with a respective sub-array and is of the type which is capable of executing two- dimensional compression of its input data. Even though the data subsamples associated with the successive rows of the bit map are non-consecutive, and therefore may contribute to a reduction in compression performance in the horizontal direction, successive data samples within each column of a sub-array are inherently more highly correlated with one another than data values that are encountered within respective rows of the original bit map. As a consequence, the two- dimensional data compression operator executed by each unit suffers no loss in output signal quality. The compressed output signals are then combined for transmission over the (facsimile) communication channel to a receiver site.
At the receiver site, successive portions of the compressed signals that have been transmitted over the communication channel from the transmitter site are coupled to respective ones of a plurality of data decompression units, which produce decompressed output signals. The decompressed output signals produced by the decompression units are coupled to a parallel- serial shift register. By serially reading out the contents of the shift register, there is obtained a reconstructed serial data stream representative of the multi-dimensional array of imagery data sample values. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of an embodiment of an imagery data communication system which employs the improved compression mechanism in accordance with the present invention; Figures 2 and 3 show respective sub-arrays of bit map data demultiplexed by the system of Figure 1; and
Figure 4 shows an enlarged section of text. DETAILED DESCRIPTION
Before describing in detail the particular improved imagery data compression system in accordance with the present invention, it should be observed that the present invention resides primarily in a novel structural combination of conventional signal processing and communication circuits and components and not in the particular detailed configurations thereof. Accordingly, the structure, control and arrangement of these conventional circuits and components have been illustrated in the drawings by readily understandable block diagrams which show only those specific details that are pertinent to the present invention, so as not to obscure the disclosure with structural details which will be readily apparent to those skilled in the art having the benefit of the description herein. Thus, the block diagram illustrations of the Figures do not necessarily represent the mechanical structural arrangement of the exemplary system, but are primarily intended to illustrate the major structural components of the system in a convenient functional grouping, whereby the present invention may be more readily understood.
Referring now to" Figure 1, a block diagram of an embodiment of an imagery data communication system which employs the improved compression mechanism in accordance with the present invention is illustrated as comprising a transmitter site 10 having an imagery data source 11 (e.g. an opto-electronic document scanner which is arranged to effect raster type scan of a document, such as successively fed pages of printed text) , data source 11 producing a series of digitally encoded signals respectively representative of successively sampled grey level values of the (text) image. As document scanner 11 typically performs a raster type scan of the document, line by line, down the page, each of the encoded signal values corresponds to a respective pixel location in a bit nap 13 of the scanned image, the bit map effectively comprising a two-dimensional array of pixel data, M (e.g. 1768) columns wide by N (e.g. 2200) rows deep. As discussed above, because the data rate of present day imagery data scanning equipment is considerably faster than the signal processing speed of the low cost compression modules customarily employed by commercial facsimile equipment, the document processing speed of that equipment has been limited to a very low volume on the order of about one page per minute. The reason for this shortcoming is the fact that the compression mechanism has operated on the data in essentially the same serial (raster) format as by the imagery data source. Even with multiline, two- dimensional image compression, the overall processing speed has been constrained by its slowest component, the compression module.
As described above, in accordance with the present invention, this limitation in document processing speed of conventional facsimile transmission systems is dramatically increased by effectively subsampling or subdividing bit nap 13 into a plurality of sub-arrays of data, successive ones of the data contents of the sub-arrays corresponding to every kth data value of the original nap. For this purpose, the original imagery data bit map is coupled to a demultiplexer'15, K respective output ports 17-1...17-κ of which are coupled to a plurality of data compression units 21-1...21-K, each of which is capable of carrying out two-dimensional compression on the sub-array of data applied to it. As mentioned previously, a respective one of compression units 21-1...21-K may be a readily commercially available unit, commonly employed in mass market facsimile equipment and capable of compressing data supplied to it at a compression rate (e.g. one to five Mb/s) that is a fraction of the transmission data rate (e.g. 10 - 12 Mb/s) from imagery data source 11.
Under the control of an associated microcontroller 23, demultiplexer 15 subdivides bit map 13 into K sub-arrays of pixel data. For purpose of simplicity of a non-limiting illustration, letting K=2, the sub-divided bit map may be demultiplexed into a pair of respective sub-arrays 31 and 32, as diagrammatically illustrated in Figures 2 and 3," respectively. As noted previously, where the image represented by the pixel data is a typical document transmitted by facsimile, such as a page of alpha numeric characters, there is a substantial inherent high correlation property among successive data samples, due to the 'elongated' nature of the text, in the vertical or 'down the page' direction, as exemplified by portions of alpha numeric characters lying along line L in the enlarged section of text shown in Figure 4. Consequently, even though, for respective rows of the bit map 13, the data subsamples of sub-arrays 31 and 32 are non-consecutive (e.g. pixel values PO,0, PO,2, P0,4, P0,6.... of row 0 of sub-array 31 shown in Figure 2) and therefore may contribute to a reduction in compression performance in the horizontal direction, successive data samples within each column of a sub-array (e.g. pixel values PO,0, Pl,0, P2,0, P3,0, ..., Pn,0 of column 0 of sub-array 31) are inherently more highly correlated with one another than data values that are encountered within respective rows of the original bit nap 13. As a consequence, the two- dimensional data compression operator executed by each compression unit 21 suffers no loss in output signal quality. The compressed output signals from compression units 21 are coupled to an output multiplexer 25 to be combined for high data rate transmission (e.g. on the order of 10-12 Mb/s) via a (digital telecommunications) transmitter modem 28, over a (facsimile) communication channel 40 (e.g. digital telephone channel) to a receiver site 20. At the receiver site 20, a receiver modem 42 outputs the compressed data signals that have been transmitted over communication channel 40 from transmitter site 10 to a demultiplexer 44, which, under the control of a receiver site microcontroller 43, controllably separates the incoming compressed data stream into respective output segments for application, via output ports 44-1...44-K, to a plurality of data decompression units 46-1...46-K. Like the compression units within the transmitter site 10, each of decompression units 46-1...46-K may be a readily commercially available unit, commonly employed in mass market facsimile equipment and capable of effecting a two-dimensional decompression of data supplied to it at a compression rate (e.g. one to five Mb/s that is a fraction of the transmission data rate (e.g. 10 - 12 Mb/s) over channel 40.
The decompressed output signals produced by the decompression units 46 are coupled to parallel input ports 52-1...52-K of a parallel-serial shift register 55. As the contents of shift register 55 are serially read out over serial output data, there is obtained a reconstructed serial data stream representative of the original bit map of imagery data sample values. As will be appreciated from the foregoing description, by subsampling high data rate imagery data into respective sub-arrays prior to data compression, ' it is possible to employ low cost readily available compression units whose processing speed is considerably less than the transmission data rate. Namely, because the data rate of successive data values within the subsampled arrays is only a fraction of the rate at which successive data values are supplied by the optical scanning device and transmitted over a facsimile communication channel, it is possible to make use of low cost compression units, without adding considerable buffer memory capacity at each end of the compression, decompression process. While we have shown and described an embodiment in accordance with the present invention, it is to be understood that the same is not limited thereto but is susceptible to numerous changes and modifications as known to a person skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are obvious to one of ordinary skill in the art.

Claims

WHAT IS CLAIMED
1. A method of processing multidimensional image representative data signals, respective ones of which are definable in the form of a two-dimensional map array of M columns by N rows of pixel data values, comprising the steps of:
(a) subsampling said array of data signals into respective sub-arrays of pixel data signals, so that the rate of occurrence of successive pixel data signals in a respective sub-array is lower than in said map array, but which is processing speed-compatible with the compression speed of a respective one of a plurality of two-dimensional data compression units,- b) coupling respective sub-arrays of pixel data signals to respective ones of said plurality -of two-dimensional data compression units, so as to effect a parallel compression of the each of said sub-arrays of subsampled data signals, each of said compression units producing compression output signals representative of a compressed sub-array of pixel data signals; and
(c) combining the compression output signals produced in step (b) to produce a composite compression signal representative of said multidimensional image representative signals.
2. A method according to claim 1, further comprising the steps of;
(d) transmitting said composite compression signal to a receiver site; (e) at said receiver site, receiving said composite compression signal and separating said composite compression signal into a plurality of compressed signals representative of said sub-arrays of pixel data signals; (f) coupling respective ones of said compressed signals to respective ones of a plurality of two-dimensional data decompression units, so as to effect a parallel decompression of the each of said compressed signals representative sub-arrays of subsampled data signals, each of said decompression units producing decompressed output signals representative of a respective sub-array of pixel data signals; and (g) combining said decompressed output signals to recover multidimensional image representative data signals.
3. A method according to claim 1, wherein step (d) comprises transmitting said composite signals to said receiver site at a data rate in excess the compression speed of a respective one of said . compression units.
4. A method according to claim 1, wherein successive ones of the data signals of a respective sub-array of data correspond to every kth data value of said data map.
5. A method according to claim 1, wherein said multidimensional image scanned by an optical scanning device to derive image representative data signals representative of alpha-numeric text the shapes of the characters, of which to be more high correlated in a direction that -is generally orthogonal to the direction in which the text is optically scanned to produce said image representative signals.
6. A method according to claim 5, wherein successive data signals within each column of a sub- array are more highly correlated with one another than data signals that are encountered within respective rows of said data map.
7. A method according to claim 2, wherein step (g) comprises coupling said decompressed output signals to parallel inputs of a parallel-to-serial shift register unit and serially reading out said decompressed output signals therefrom to recover said image representative data signals.
8. A method according to claim 1, wherein the number of said compression units is determined in accordance with the ratio of the data rate of said image representative signals to the signal processing speed of a respective one of said compression units.
9. A system for processing multidimensional image representative data signals, respective ones of which are definable in the form of a two-dimensional map array of M columns by N rows of pixel data values, comprising: a data signal subdividing device, to which said array multidimensional image representative data signals is coupled, which subsamples said array of data signals into respective sub-arrays of pixel data signals, so that the rate of occurrence of successive pixel data signals in a respective sub-array is lower than in said map array, but which is processing speed- compatible with the compression speed of a respective one of a plurality of two-dimensional data compression units; a plurality of two-dimensional data compression units, respective ones of which are coupled to receive respective ones of said sub-arrays of pixel data signals, and carrying out a parallel compression of the each of said sub-arrays of subsampled data signals, each of said compression units producing compression output signals representative of a compressed sub-array of pixel data signals; and a compression output signal combining unit - which combines said compression output signals to produce a composite compression signal representative of said multidimensional image representative signals.
10. A system according to claim 9, further comprising: a transmitter coupled to said compression signal combining unit and transmitting said composite compression signal over a communication channel to a receiver site.
11. A system according to claim 10, further comprising, at said receiver site, a receiver unit which receives said composite compression signal, a demultiplexer which separates said composite compression signal into a plurality of compressed signals representative of said sub-arrays of pixel data- signals, and a plurality of two-dimensional data decompression units, to respective ones of which respective ones of said plurality of compressed signals are coupled, so as to effect a parallel decompression of the each of said compressed signals representative sub-arrays of subsampled data, each of said decompression units producing decompressed output signals representative of a respective sub-array of pixel data signals, and a signal combining unit which combines said decompressed output signals to recover multidimensional image representative data signals.
12. A system according to claim 10, wherein said transmitter transmits said composite signals to said receiver site at a data rate in excess the compression speed of a respective one of said compression units.
13. A system according to claim 9, wherein said data signal subdividing device comprises a demultiplexer which couples every kth data signal of said map array to a respective one of said compression units.
14. A system according to claim 9, wherein said multidimensional image representative data signals are derived from an optical scanning device and are representative of alpha-numeric text the shapes of the characters of which to be more high correlated in a direction that is generally orthogonal to the direction in which the text is optically scanned by an optical scanning device to produce said image representative signals.
15. A system according to claim 14, wherein successive data signals within each column of a sub- array are more highly correlated with one another than data signals that are encountered within respective rows of said data map.
16. A system according to claim 10, wherein said compression signal output combining unit comprises a parallel-to-serial shift register to parallel inputs of which said decompressed output signals are coupled, said shift register serially reading out said decompressed output signals therefrom to recover said image representative data signals.
17. A system according to claim 9, wherein the number of said compression units is determined in accordance with the ratio of the data rate of said image representative signals to the signal processing speed of a respective one of said compression units.
18. A system according to claim 11, wherein said communication channel comprises a facsimile transmission communication channel.
19. A method of processing multidimensional image representative data signals, respective ones of which are definable in the form of a two-dimensional nap array of M columns by N rows of pixel data values, comprising the steps of:
(a) subsampling successive rows of said map array into respective sub-arrays of pixel data signals of M columns by P rows of pixel data signals, so that the rate of occurrence of successive pixel data signals in a row of a respective sub-array is lower than the rate of occurrence of pixel data signals in a row of. said map array, but which is processing speed- compatible with the compression speed of a respective one of a plurality of two-dimensional data compression units; b) coupling respective sub-arrays of pixel data signals to respective ones of said plurality of two-dimensional data compression units, so as to effect a parallel compression of the each of said sub-arrays of subsampled data signals, each of said compression units producing compression output signals representative of a compressed sub-array of pixel data signals; and
(c) combining the compression output signals produced in step (b) to produce a composite compression signal representative of said multidimensional image representative signals.
20. A method according to claim 19, wherein said multidimensional image scanned by an optical scanning device to derive image representative data signals representative of alpha-numeric text the shapes of the characters of which to be more high correlated in a direction corresponding to the direction of the columns of said bit nap array and a sub-array, which is generally orthogonal to the direction in which the text is optically scanned to produce said image representative signals.
21. A method according to claim 19, wherein the number of said compression units is determined in accordance with the ratio of the data rate of said image representative signals to the signal processing speed of a respective one of said compression units.
EP19910902065 1989-12-22 1990-12-17 High speed compression of imagery data Withdrawn EP0460188A1 (en)

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