CA1157565A - Multilevel processing of image signals - Google Patents

Abstract

Abstract of the Disclosure A graphic arts image comprising a plurality of regions, each region having a characteristic multilevel intensity, hue, texture or the like, is sampled and coded using samples along two consecutive scan lines. Individual code words are generated for the beginning, or head, of each run defining the start of A vein or boundary of a region of contiguous like-valued samples along each line and other code words are used for connecting information relating to samples on adjacent lines defining continuations of the boundary for the same region. Other code words identify the characteristic intensity or the like of the region, and a final type of code word identifies the end of the vein. Because the present method and apparatus advantageously codes each internal boundary between adjacent regions only once, an increase of efficiency by a factor approaching two is realized over techniques previously used.

Description

5~5~5 - 1 - FRANK, A. J. S
MULTILEVEL PROCESSING ~F I~A~ SIGN~LS
Background of the Invent.ion 1. Field of the Invention The present invention relates to apparatus and s methods for the coding and storing of graphical information. More particularly, the present invention relates to apparatus and methods for generating and storing coded representations of high fidelity multilevel graphic art images suitable .Eor the photocomposition of printed 10 materials. Because of the ease of generating ef~icient codes using the present invention, applications including real time facsimile and teleconferencing transmission, long term storage of x-ray or like data, and machine cutting operations are possible.

2. Description of the Prior Art __ Recent years have witnessed greatly increased usage of automatic means for composing and printing page copy for use in directories, catalogs, maga~ines and other printed works. An important aspect of such 20 photocomposition schemes is the coding and storage of machine-compatible signals representative of graphical source information. In particular, when pictorial information and/or high-resolution type fonts are to be used, it has been found necessary to identify by scanning ~5 with great particularity the individual graphical entities associated with the source material. To permit the further processing of these data it has usually been necessary to store them in memories having substantial capacity. Often these data are stored for long times, as when they are to be used in successive issues of a book, magazine or the like. Because typical published materials, especially photographic or other picture materials are so diverse, and because the information content of such materials is so great, the volume of data re~uired to be stored is potentially very large. It is especially important therefore that these data be stored in as efficient a manner ~s possible.
A number of particular coding and storage schemes 7~5 - 2 - F ~ K, A. J. 5 have been developed for efficiently storing and transmitting information. For example, the variable length codes described in Elias, "Predictive Coding", IRE
Transactions Information Theory, ~arch 1955, have proved to be useful in many variations. The well-known HuffMan codes described, for example, in Huffman, "A Method ~or the Construction of Minimum Redundancy Codes," Proceedings I.R.E., September 1952, pp. 1098-1101, and Fano, Transmission of Information, The MIT Press, 1961, . _ _ 10 pp. 75-81, offer optimum efficiency under particular circumstances. The application of these techniques to graphical information has generally been limited to one-dimensional coding, i.e., coding of signals associated with a single scan line in the source copy.
~.S~ pa-tent 3,461,231 issued August 12~ 1969 to R. V. Quinlan describes a system for performing limited two-dimensional encoding. However, his techniques are limited to transmittin~ only an indication of the differences between data corresponding to two successive 20 scan lines. ~ related technique is presented in Tyler, "Two Hardcopy Terminals for PCM Communications of Meterorological Products," Con~erence Record, 1969 International Conference on Communications, June 9-11, .
1969, pp. 11-21 through 11-28. Tyler encodes his data (meteorological information) in terms of differential lengths for run lengths on two successive scan lines.
Huang, "Run-Length Coding and its Extensions," in Huang and Tretiak (Eds.), Picture Bandwidth Compression, Gordan and .. _ . .. ._ Breach, New York 1972, pp. 231-264, discusses some 30 extensions to the work of Tyler.
Other two-dimensional coding of picture information is described in D. N. Graham, 'IImage Transmission by Two-Dimensional Contour Coding, 1l Proceedings of the IEEE, Vol. 55, No. 3, March 1967, 35 pp. 336-345.
The above-cited Quinlan and Tyler references indicate a need to determine not only what is encoded, i.e., which parameters are encoded, but also how, exactly, ~ 1~7~$5 these parameters are to be encoded. The latter aspect of the problem is also treated in U.S. patent 3,643,019, issued February 15, 1972 to J.P. Beltz. Particular reference is made by Beltz of the applicability of his techniques in commercial photocomposition systems such as the RCA VIDEOCOMP (trade mark) Series 70~800. Although Beltz applies a variable-length coding to segments defining a "zone", each such zone is the area defined by a single scan line, i.e., he does not attempt to extend his results to two-dimensional coding. Likewise, though Graham and Huang speak of Huffman codes, their application is to very specific geometric entities.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention there is provided apparatus for coding a two-dimensional information field having a plurality of regions, each region having one of a plurality of different graphical values, comprising scanning means for determining, on a path by path scan across said field, the graphic value of successive pels along each of said paths, storage means for simultaneously storing the graphic values so determined for two successive path scans across said field, and means for comparing the stored graphic values of pels from one of said scanned paths with those from the other of said paths, and including means, utilizing the stored values and the results of said comparison, for generating for each scanned region (a) a first binary electric code representative of the length of a constant-value run along a scanning path; (b) a second binary electric code representative of the graphical value of said region, and (c) a third binary electric code representative of the end of the last scanning path scanning said region; and for any scanning path, a fourth binary electric code eepresent-ative of the conne~tivity of a constant-value run along said path to a constant-value run along a previous scanning path.

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- 3a -In accordance with another aspect of the invention there is provided a method for coding a two-dimensional information field having a plurality of regions, each region having one of a plurality of different graphical values, comprising determining, on a path by path scan across said field, the graphic value of successive pels along each of said paths, simultaneously storing the graphic values so determined for two successive path scans across said field, comparing the stored graphic values of pels from one of said scanned paths with those from the other of said paths, and, utilizing the stored values and the results of said comparison, generating for each scanned region (a) a first binary electric code represent-ative of the length of a constant-value run along a scanning path; (b) a second binary electric code represent-ative of the graphical value of said regionr and (c) a third binary electric code representative of the end of the last scanning path scanning said region, and for any scanning path, a fourth binary electric code represent-ative of the connectivity of a constant-value run along said path to a constant-value run along a previous scanning path.
In accordance with one embodiment of the present invention, a visible image, e.g., a photograph9 typed copy, line drawing or any combination of these or like images, is scanned, sampled and converted into multilevel quantized signals. The image or field typically comprises a plurality o~ regions or blobs, where the level (hue, brightness, texture, or the like) is constant or of a defined content wi~hin any given region; different regions, however, will, in general have one of a plurality of levels. In coding region boundaries and contents (and subsequently decoding them) apparatus and methods in accordance with a typical embodiment of the present invention operate on a field sequentially from top to bottom only once, accessing at most samples from two .,~ .

1 ~7~

lines at a time. An encoder capitalizes on correlation in two dimensions, and codes a large portion of the boundary segments only once. The resulting simplicity of logic, fast operation, small buffer requirement, and coding efficiency are particularly well-suited for implementation via special purpose hardware, or a combination of micro-processor and special purpose hardware.
BRIEF DESCP~IPTION OF THE DRAWINGS
FIGS. lA through lJ indicate various possible occurrences of veins demarking adjacent regions in an image;
FXG. 2A shows numerical pattern corresponding to values for samples of a typical image, including boundaries defining the respective regions;
FIG. 2B shows a pattern of coded words used to encode the samples of FIG. 2A in accordance with one embodiment of the present invention;
; FIG. 3 is a block diagram of processor apparatus for realizing one embodiment of the present invention;
FIG. 4A is a block diagram in detail of a portion of the apparatus shown in FIG. 3;
FIG. 4B is a flow chart illustrating the operation of the circuit of FIG. 3; and FIG~ 5 (appearing on the same sheet of drawings as FIG. 4A) is a block diagram of an alternative embodiment of the present invention.
DETAILED DESCRIPTION
1. BACE~GROUND AND DEFINITIONS
Before proceeding with the detailed description, it proves convenient to define certain terms and describe some conventions used with some regularity in the sequel.
It is well known that much information-bearing copy has only two levels of image intensity~ e.g., black and white. In other cases one or more intermediate bright-ness levels, i.e., gray levels, are used. In still othercases, multiple colors and brightness levels are used.

~ ~7~5 For present purposes, image copy will be assumed to possess any discrete number of levels. A special case will be that where only two brightness levels tconveniently black and white) occur. When actual image intensity does not equal one of the allowed discrete values, a standard quantizing operation will be used ~o "round-off" signals representing such image regions.
Although high quality reproduction of images often requires substantial continuity of all connected parts of an image/ i.e., no gaps in the reproduced image, it proves convenient in intermediate processing to use digital techniques, i.e., to treat such images as collections of discrete elements. Thus in processing a typical image there is conceptually superimposed on the image a grid of horizontal and vertical lines defining individual picture elements (pels). In practice these pels are arbitrarily, but sequentially, assigned to particular image subject matter by causing the image to be scanned by an optical or other scanning means, thereby to generate a signal indicative of the brightness level (or color, texture, or the like) occurring along a narrow scan line. A typical optical image scanning system is disclosed in U.~. Paten~ 3,445,588 issued to J.F. Nicholson on May 20, 1969. Functionally equivalent scanning apparatus i5 disclosed in the above-cited Beltz patent in connection with the RCA VIDEOCOMP (trade mark) Series 70/800 photo-composition system. Many particular scanning devices may be used ~o generate signals representative of the image intensity along a scan line.
The actual definition of individual pels is accomplished in standard practice by sampling the output of the scanner. Thus, in general, the output of a scanner is a continuous signal not unlike that associated with standard television broadcast signals. These signals are then sampled in response to periodic clock signals generated , x~ .

8 ~7~

by a source of standard design. Typical apparatus for performing such scanning and sampling operations is disclosed in my U.S. Patents 4,103,287 and 4,107,648 which issued on July 2S, 1978 and August 15, 1978, respectively.
As commonly used in television and other picture processing arts, a "run" is an occurrence of like-brightness level or like-color pels in consecutive pel positions along a scan line. Thus 1 along a typical scan line a black run begins at the fourth pel and continues through the fifteenth pel, a run of 12 black pels results.
The concept oE a run is generalized for preventive purposes to cover a sequence of samples along a scan line having the same characteristic, whether it be brightness, color, texture or any other definable characteristic. While horizontal scanning is assumed in the present disclosure, it is clear that similar runs can be defined for vertical scan lines. In further connection with the actua~
scanning, it will be assumed that each scan line proceeds from a left end to a right end. Particular pels along each scan line are identified by an abscissa coordinate integer beginning at the left with 1 and ending with N for an N-pel scan line.
2. CODE STRUCTURE O~tERVIEW
Unlike my earlier coding techniques and apparatus described in the above-identified U.S. Patents Nos.
4,103,287 and 4,107,648, the invention described presently deals with the coding oE boundaries for distinct regions in an image. These regions are alike in some fundamental way, each as having the same brightness level, color, texture, or other widely diverse state of being such as freedom from tree disease in the case of a forest image.
Above unifying theme is ~hat of a vein, like that occurring in a natural leaf. As is well known, such veins typically have beginning points, end points, branch points and the like. The present section of the disclosure will Eormalize such geometrical characteristics and in drawing 1 ~7~
- 6a -so will disclose some important structural aspects of the present coding techniques and apparatus.
FIGS. 1 A-J shows a number of possible views or windows of portions of a typical graphic arts images for illustrating the various occurrences in a leaf image. In each case one or more veins traverse the window orming distinct regions~ It is assumed that the new process operates on a horizontally scanned, digitized form of each window, and that the width of the window is known to the coding process. In overview, four types of codes are used, referred to here as I, H, C, and E codes. The various I codes identify the contents of a region, such as various gray levels or texture patterns. The va~ious H
codes give the length of the top most run of elements, ca}led the "head", of a region. The various C codes indicate how a vein at one image line connects to a vein in the previous line. In digital form, this coding procedure encodes the displacement in number of elements of a boundary from one image line to the next. The single E code indicates the bottom or end of a region. This code structure is now ~ ~5~
- 7 - FRANK, A J. S
explained in detail, tracing the various configurations that may occur by means of the images in FIGS. 1 A-J.
composite example of the code structure is then given~ and the partitioning and encoding and decoding processes and 5 apparatus are discussed.
VEINS STAR?ING AT THE ~OP
Consider first the case as shown in FIG. lA, where only one vein traverses the window, for~ing a ~oundary between two regions, 1 and 2. Starting with the lOfirst image line, code first an H code for ~he length of the head of region 1, followed by an I code identifying the region contents as "1". Next, there is an H code for the length of the head of region 2, and an I code to identify the region contents as "2". For each succeeding image line 15the runs in the line are compared with those in the previous line only. In the example in FIG. lA each image line starts with a run of l's, but the runs end at varying places, as indicated by the vein separating region 1 from region 2. Accordingly, for each image line a C code is 200utput to indicate how the vein there connects to the same vein in the previous line, and a C code is output for the vein coincident with the right side of the image. One can think of each vein as defining the right edge of a region, or equivalently as defining the length o~ the successive 25runs comprising the region.
Note that since the image width is known, it logically requires no explicit coding of region 2's right edge, which is coincident with the right side of the image.
This means that one does not strictly require an ~ code for 30a head ending at the right side of the image, or a C code for a run that is not a head but ends at the right side of the image. ~owever, these codes are indeed included ~or two reasons.
Firstly, in order to exclude such codes we would have -to introduce considerable logic complexity in apparatus for hoth the encoding and decoding processes.
This increased implementation complexity is not generally warranted by the associated small increase in coding ~ 1~7tSB5 - 8 - F ~ K, A. J. 5 efficiency. At best the savings in bits per pel is KA/A2 or K/A, where K is the average bits for the H or C code for the run at the end of the line, and A is the number of lines.
Secondly, a reason for the inclusion of the H code explicitly has to do with the sequence of codewords and the total codebook structure. Namely, if an I code always follows an H code, and if an I code never follows any code other than an H, then the codes may be separated lOinto two sets, one containing the I codes, and the other containing all other codes. Two codewords, one from each set, need not be distinct. In other words, separate codebooks may be used for the two sets. This results in higher coding efficiency than if all the codewords had to be distinct. Alternatively, if greater efficiency results, the order of the H and I codes can be reversed, and thus the H codes rather than the I codes isolated into one codebook. In any case, for a head extending to the right side of an image, a special H code, Ho~ is established 20signifying no particular head length, but rather whatever length is required to extend the head to the end of the image line.
Multiple veins as shown in FIG. lB merely cause the addition for each such vein of an H code and an I code, 25 and a set of C codes delineating the course of the vein progressing downwards. These various codes advantageously appear in the output code stream in the order in which their respective conditions arise in the left-to-right, line-by-line comparison process. Thus, for FIG. lB, we 30output an H code and an I code for region 1, an ~1 code and an I code for region 2, and Ho code and an I code for region 3, and then for each successive image line three C codes for the right edges of regions 1, 2, and 3 respectively.
BIFURCATING VEINS
A vein that bifurcates forms a new region, such as region 3 in FIG. lC. In this case, the left leg of the

3 ~75~P

- 9 - ~R~NK, A. J. S
bifurcation is taken as a continuation of the parent vein, and the right leg is treated as a new vein. Thus, for the first image line in which region 3 occurs, output first a C code to indicate a connection to the parent vein in the 5previous image line. It can be seen that this vein continues to demarcate the right edge of region 1.
Following this an H code and an I code for region 3 are output. This establishes the new vein deEining the right edge of region 3. This is followed by a C code for the lOright edge of region 2~ For each successive line three C codes are output for the right edge of regions 1, 3, and 2 respectively.

A new vein may also start at the left or right 15side of the image, as shown in FIG. lD. Consider first region 3 cutting in from the left. For the image line immediately previous to the one containing the head of region 3, two C codes are output for the right edges of regions 1 and 2 respectively. Output next are an H code 20and an I code for region 3, and two C codes for the right edges of regions 1 and 2, respectively. Eor each image line thereafter until region 4 is reached, three C codes are output Eor the right edges of regions 3, 1, and 2 respectively. The vein marking the left of region 4 is 25 taken as a continuation of the right edge of region 2, i.e., as a continuation of the vein coincident with the right side of the image line containing region 4. First, three C codes for the right edges of regions 3, 1, and 2, respectively are output. Output next are the Ho and 30 I codes for region 4. For each remaininy image line we output four C codes for the right edges of regions 3, 1, 2, and 4 respectively.

A pair of veins may also start in the interior of 3s an image, forming a new region, such as region 3 in FIG. lE. At the point that region 3 starts, region 1 divides into two legs, one to the left and one to the right ~ ~75~5 - 10 - P ~ K, ~. J. 5 of region 3. Accordingly, from this point onwards three veins are nee~ed for regions 1 and 3, one each for the right sides of the two legs of region 1 and one for the right side of region 3. This need is handled by forming a 5 new region, 4, for the right leg of region 1, as shown in FIG. lF. For the first image line in which region 3 occurs a connection is coded for the vein which progresses from the right side of the upper part of reg~on 1, along the top of region 4, and along the right ~ide of the left leg of 10 region 1. This vein is marked by arrows in FIG. lF.
Output next are the H and I codes for region 3, and then the H and I codes for the region 4, and finally the C code for the right edge of region 2. The I codes for regions 1 and 4 are, of course, identical. Eor each subsequent image 15 line, four C codes are output for the right edges of regions 1, 3, 4 and 2 respectively.
VEINS MERGING IN THE INTERIOR
An analogous situation to that just described occurs where a pair of veins coalesce in the interior of an 20 image, thus ending a region such as region 2 in FIG. lG.
In this case region 1 initially has two legs, which join at the point that region 2 ends. Up to this juncture three veins are needed for regions 1 and 2, one each for the right sides oE the two legs of region 1, and one Eor the 25 right edge of region 2. ~s in the previous case a separate region, 5, is formed for the right leg as shown in FIG. lH.
For the first image line H and I codes are output for each of the regions 1, 2, 5, and 3, respectively. As before, the I codes for component regions, 1 and 5, are identical.
30 For subsequent image lines up to and includiny the last line containing region 5 we output C codes for the right edges of regions 1, 2, 5, and 3, respectively. For the image line following the last one in which region 5 occurs, output first is a C code for the vein which progresses from 35 the right edge of the upper left leg of region 1, then along the bottom of regions 2 and 5~ and along the right edge of the lower part of region 1~ This vein is marked with arrows in FIG. lH. Output next are two E end codes ~ ~7~S5 - 11 ~ FRANK, A. J. 5 for regions 2 and 5, and finally a C code for the right edge of region 3.
Eor each image line thereafter until region 4 is reached, t~o C codes are output for the right edges of Sre~ions 1 and 3, respectively. For the image line containing the first run of region 4, C codes are output for the right edges of regions 1, and 3 and the Ho and I codes for region 4. For each succeeding line up to and including the one containing the last run of region 3, lOthree C codes are output for the right edges of regions 1, 3, and 4, respectively. At this point a case may be seen in which two veins meet and continue along as single path.
E~or the image line following the last line in which region 3 occurs, a C code is output for the right edge of 15region 1, an E code for region 3, and a C code for the right edge of region ~. For each remaining line two C codes are output for the right edges of regions 1 and 4, respectively.
VEINS ENDING AT THE SIDE
Veins merging into the side of an image mark the end of a region, as shown in FIG. lI. Consider first region 1 ending on the left side. For the last image line in which region 1 occurs t C codes are output for the riyht 25edges of regions 1, 2, 3 and 4, respectively. For the next image line, output an E code for region 1, followed by the C codes for the right edges of regions 2, 3, and 4 respectively. For each succeeding image line up to and ; including the last line in which region 4 occurs, output 3QC codes for the right edges of regions 2, 3 and 4 respectively. ~imilarly, for the next line, output C codes for the right edges of regions 2 and 3 respectively. As region 3 in this image line extends to the right side of the line, it simultaneously means that region 4 ends.
35 Hence in this case no E code is needed for region 4O The same condition applies if the run extending to the right side of the image is the head of a new region. Also, more than one region may be ended in this manner. Thus, - 12 - ~ ~ K~ A. J. 5 proceecling downward in FIG. lI past the start of region 5 and continuing past the image line containing the last runs of regions 5 and 3, it may be seen that these regions are automatically ended without E codes merely by the 5 specification o~ the head of region 6.
VEINS ~ND RUNS SPAN~ING FUL~ LINES
FIG. lJ shows a ~inal configuration where the vein and some of the runs span a full image line. For the first image line the Ho and I codes are output for 10 region l. For each subsequent line in region l a C code is output for the region's ri~ht edge, which is coincident with the right side of the image. For the first line of region 2, ~O and I codes are output for region 2. As indicated before, no F code is required for re~ion l in 15 this case. For each succeeding line in region 2 up to the line just before the start of re~ion 3 a C code is output ~or the right edge of region 2. The vein marking the left of region 3 is taken as a continuation of the right edge of region 2, which is coincident with the right side of the 20 ima~e. This is similar to the configuration shown in ~IG. lD. Accordingly, for the next image line, outputs are a C code for the right edge of region 2 and the Ho and I
codes for region 3. For each remaining line the output is two C codes for the right edges of regions l and 3, 25 respectively.
A CO~IPOS ITE EXAMPLE
FIGS. 2A and 2B give a composite example of the partitioning and coding of a two-dimensional field.
FIG. 2A shows the two-dimensional field and the explicitly 30 coded veins, and FIG. 2B shows the associated codes. The codes appear in a two-dimensional layout for easy reference to the original field. In practice they may form a linear serial stream.
For each ~ code in FIG. 2B the associated vein in 35 FIG. 2A is shown as a line along the top and right side of the associated run~ For each C code the vein is shown continued down the right side of the run. The start of a vein is marked by a ball, and the end by an arrowhead. To 7~
- 13 - ~RANK, A. J. 5 show clearly the path of individual veins, those vein segments which are coincident in FIG. 2A are shown slightly offset from each otner. These segments, which require double encoding, occur in a horizontal direction only.
The subscripts on the codes in FIG. 2B identify the reyion associated with the code. For example, E15 is the H code demarking the beginning of region 5, the region having inten~ity or color 5. A C code traces ~he vein along the right boundary of a region and bears the 10 subscript of that region. In this example, the simplest condition is used for connection of veins at the right edge of runs in two successive lines. That is, the two runs under comparison have the same region identification codes.
~ith this condition, an image J pels wide may have 2 J-l 15 possible C codes. In this case the two runs may be geometrically separated from each other, such as the two runs of region 1 in the third and fourth image lines. If desired, regions like this may be avoided, or the partitioning otherwise altered by placing additional 20 restrictions on the runs under comparison. For example, one may require that the right ends of the runs be within K
elements of each other, or that the runs overlap by at least L elements, or that the number of elements in the second run be no more than M times larger and no less than 25 N times smaller than the number of elements in the first run. ~estrictions such as these generally increase the number of regions defined. They may also decrease the number of different values for -the C codewords.
Inspecting FIG. 2A, note that the encoding itself 30 need not explicitly mark the veins along the bottom of particular regions, such as regions 5 and 8, and those at the bottom of the image. If desired, as for example in a machine cutting operation, these lines can be easily added in the decoding process. Thus, upon reaching the end of a 35 vein, signaled by an E code, the vein can be extended to the left until the abutting region or the left side of the image is reached. In all cases, of course, the line defining the left side of the image must be added. Of ~ 1575~

- 1~ - F ~ K, A. J. 5 possible importance also to a cutting operation, note that the resulting veins do not crisscross. This is always true and results ~rom progressing only from left to right in comparing the runs on two successive image lines. This is sdiscussed in further detail below.
3. PARTITIONING ~ND ENCODING PROC~SS (OVERVIEW) The coding structure for the various geometric configurations of a digitized two-dimensional Eield has been described. Described now is a concomitant process lowhich partitions and encodes a field in accordance with this code structure.
For the firs-t image line, one need simply output the appropriate H and I codes for each distinct run of like elements in the line. One then places this line in a 15buffer A and reads the next line into a buffer B. For each buffer a pointer is maintained, which at any given time in the process addresses one of the runs in the associated buf~er. At the start of the comparison between the contents of the two buffers, the pointers are se-t at the 20lef~ end of their respective buffers. One then compares the two runs thus addressed, and outputs none or some codewords depending upon the comparison. Following this one or both pointers are progressed to the next run in the line. The comparison is now made on the two runs currently 25addressed, and codewords output-ted as called for, and one or both pointers progressed to the next run in the line.
Pointer movement is always from left to right. These actions continue until both pointers reach the right end o~
their respective buffers. When this occurs, buffer B is 30changed into buffer A, the next image line i9 read into buffer B, and the comparison process repeated. This cycle continues until all image lines are processed.
The comparisons made between two runs addressed by the buffer pointers are as follows. If the runs ha~e 35matching region identifications, then output the appropriate C code and progress the pointer for each buffer to the next run to the right in the buffer, or to the ~nd of the buffer if the run just processed is the last one in ~ ~7~
- 15 - ~RANK, ~. J. 5 the buffer. Assuming a run ls left in each buffer, restart the comparison process. For runs with matching region identifications, one ma~ also place further restrictions on the connectivity as dictated by a particular application, Sas discussed previouslyA
Continuing with the comparison process, if the two runs addressed by the buffer pointers do not have matching region identifications, then search to the right or the buffer A run to determine i~ buffer A contains a run within a "specified" distance and which has the same region identification as the buffer B run. This search does not move the buffer A pointer, but is executed with an auxiliary mechanism. The "specified" distance referred to is in general some function of the positions of the 15buffer A and buffer B runs addressed, again as dictated by a particular application. For example, the search may include only one run to the right of the buffer A run, and/or the search may include all buffer A runs whose left ends are to the left of or at the right end of -the buffer B
20run. The search ends, of course, if the end of buffer A is reached. In any case, if this search produces a buffer A
run with the same region identification as the buffer B run and which satisfies any other desired connectivity conditions, one then outputs an E code for each run in 25bufer A starting with the buffer A run addressed by the buffer A pointer up to and including the run im~lediately to the left of the matching run produced hy the searchO Then progress the buffer A pointer to the matching run, and O~ltpUt a C code. Each buffer pointer is then progressed to 30the next run in the buffer, or to the end of the buffer if the run just processed is the last one in the buffer. If a run is left in each buffer, restart the comparison process.
On the other hand, if the search indicated above does not yield a connecting run, then the run addressed in 3sbuffer B is the head of a new region. Accordingly, one outputs the appropriate ~ and I codes, using the Ho and I
codes if the run ends at the right end of the line. After outputting these codes, progress only the bufEer B pointer 1 ~5~5~

- 16 - ~RANK) A. J. 5 to the next run to the right in the buffer, o~ to the end of the buffer as applicable. If a run is left in each buffer, restart the comparison process.
If the runs in buffer B exhaust before or at the 5same time as the runs in buffer A, bypass any remaining runs in buffer A, change buf~er B to buffer A, read the next line into buffer B, reset the buffer pointers to the left end of the buffers, and start the run comparisons anew. If the runs in buffer A exhaus-t before the runs in buffer B, then all the remaining runs in buffer B are heads of regions. Here, the appropriate H and I codes for each remaining run are outputted, using the Ho and I cocles for the last run. Buffer B is then changed into bu~fer A, the next image line read into buffer B, the pointers reset, and 15the run comparisons continued.

4. DECODING PROCESS (OVERVIEW) A process for decoding a bit stream generated by the previous encoding process is now described. Buffers A
and B, and associated pointers, are used as before.
20Initially, a parsing process is used which accesses the code bit s~ream for the next codeword and identifies it as a particular H, C, E, or I code. To insure efficient parsing and codeword identification, the technique for decoding variable length codes described in my U~ S.
2Spatent 3,8~3,847, granted May 13, 1975, may be used. The initial codewords in a bit stream specify the head lengths and region identification for the runs in the first line, which are entered into buffer B. ~ach time the buffer is filled, "end of line" processing takes place, i.e., the 30buffer contents are used/ buffer B is changed into buffer A, and the pointers are reset. Using buffer B may mean, for example, displaying it on a screen, generating hard copy, or storing it for subsequent processing. After thus handling the first line, codewords are retrieved from 3sthe bit stream, runs entered into buffer B, and the buffer pointers progressed as dictated by the codewords and the contents of buffer A. Again, upon filling buffer B/ "end of line" processing is executed, and the process of filling ~a~
.~, - 17 _ buffer ~ is restarted. This cycle continues until the bit stream is exhausted.
The action invoked b~ the various codes may be summarized as ~ollows. For an H code, the next codeword sfrom the bit stream is retrieved. This is always an I code. Next entered into buffer B is a run of length and type indicated by the H and I codes, starting at the position addressed by the buf~er B pointer. If this run ends before the end o~ the line, the buffer B pointer is rogressed one position to the right of the newly entere~
run, and the next codeword is retrieved. If the run ends at the end of the line, "end of the line" processing is executed.
For a C code, the buffer A pointer is progressed 15to the right end of the run currently being addressed, and the C code is applied to this position to fix the right end of the run which is to be entered into buffer B. Using the same region identification as the run addressed in bu~fer A, the run is then entered into buffer B, starting 20at the position addressed by the buffer B pointer. If this run ends before the end of the line, the buffer B pointer is progressed to one position to the right of this run. In this case, if the buffer A pointer is not at the end of the line, it is also progressed one position to the right of 2sits current position. If the run just entered ends at the end of the line, "end of line" processing is executed.
For an E code, the buffer A pointer is merely progressed to one position beyond the end of the current run addressed by the pointer, and the next codeword is 30retrieved.
IMPLEMENTATION
.
Turning now to the actual processing methods and apparatus of this invention, it will be seen that FIG. 3 depicts a general block diagram of an embodiment of 35apparatus for encoding picture information in accordance with the present invention. FIG. 4 is a diagram, showing the operational flow within the apparatus disclosed by FIG. 3, i.e., the various states that the apparatus assumes ~ ~5~

- 18 - FR~NK, A. l. S
and the operations performed within each state. FIG. ~ may also be viewed as a flow chart from which a computer program may be constructed and implemented on a yeneral purpose computer to substitute for much of -the hardware of

5 FIG. 3.
At the logical beginning, or "front end", of the encoder on FIG. 3 is scanner 7100 which operates on an image to be encoded and scans the image sequentially, line by line. Scanner 7100 may be an optical scanner or a 10 nonoptical scanner. A typical optical scanner is disclosed in U. S. patent 3,445,588 issued to J. F. Nicholson on May 20, 1969. Functionally equivalent scanning apparatus is disclosed in the above cited Beltz patent in connection with the RCA VIDEOCOMP, series 7U/800, photocomposition 15 system. Many other devices may be used to generate signals representative of diverse states of an image along a scan line.
Thus, as other scanners, scanner 7100 provides a sequence of tone indications for individual picture 20 elements. The actual definition of individual picture elements (pels) is accomplished, as in standard practice, by sampling the output of the scanner. Thus, the scanner internally develops a continuous signal not unlike that associated with standard television broadcast signals. The 25 associated circuits within the scanner sample the signal with a periodic clock signal, and ~uantize the sampled signal to represent image pels. It will be assumed that the scanner produced sequential level signals having one of n=2k values. In a typical case n=16 so k=4 binary signals 30 are used for each sample. Again, "level" can be interpreted to be color, texture, or the like.
Operation of the encoder of FIG. 3 alternates between two phases, input and processing, under control of control element 7300. In the input phase, the contents of 35 a shift-right/shift-left register BB are transferred to shift-right/shift-left register AA through switch 7220, line 7201, and switch 7230, and scanner 7100 applies its output signal to register BB through a switch 7210. The " ~ ~$75~

- 19 ~ ~RANK, A. J. S
scanner and switches 7210, 7220, and 7230 are controlled by line 73~1. In the processing stage, switches 7210, 7220, and 7230 are switched so that register AA cycles upon itself, in either direction, through switch 7230, and sregister BB cycles UpOIl itself, in either direction, through switches 7210 and 7220.
Processing of the scanned signals to develop the desired output codes is achieved by connecting output signals from register AA and an output signal ~rom lOregister BB to a processor 7200, and by controlling registers AA and BB and processor 7200 with a control element 7300. Specifically, register BB is controlled with shift-right/shift-left clock signals 7302 and 7303 and register AA is controlled with shift-right/shift-left clock 15signals 7304 and 7305, and processor 7200 interacts with control element 7300 via a two-way bus line 7306.
Processor 7200, which is the main processing unit of the encoderl processes the information of each current scan (located in register BB) by comparing it to the 20information of the preceding scan (located in register AA).
FIG. 4A diagrams the main elements of processor 7200. Register RAP contains the rightmost signals of shift register AA. These K signals specify the level of the rightmost pel indicated in AA. Thus in the typical case 25cited previously, it contains four binary signals to indicate one of sixteen levels. Register RA contains the next rightmost K signals, specifying the next pel in AA.
Similarly, registers RBP and RB contain the binary signals for the rightmost and next to rightmost pels in shift 30register BB, respectively. Counter KA keeps track of the register AA pel ~eing processed and provides an indication whenever the line in register AA has been processed completely. Counter KB serves the same purpose for the pels in register BB. Register RKB is used to store the 35position of the start of a run of like numbered pels less 1, and is used in conjunction with counter KB to give the length in number of pels of a head run.
When data are shifted into register BB for the " ~ ~5~S8~
- 20 - FRANK, ~. J. 5 first image line, the processor of FIG. 3 is placed in STATE 0, corresponding to block ~500 in FI~ . In this case, all of the runs in the image line are to be coded as head runs. At block 7500 the counter KA is set to L+l.
5~rhis will force subsequent tests at block 7515 to route to block 7520. Block 7500 also indicates that counter K~ is to be set to the i~itial value of 0. Then STATE O
terminates and entry is made to STATE 3, corresponding to block 7510.
Subsequently, when data are shifted into registers AA and BB from register BB and scanner 71~0, respectively, the processor of FIG. 3 is placed in ST~TE 1.
This state corresponds to block 7501 in FIG. 4B, where counters KA and KB are initialized to 0. Then STATE 1 15terminates and STATE 2 corresponding to block 7505 is entered. Block 7505 indicates that register AA is to be shifted right until a transition T frosn one level to the next occurs. This is accomplished by repetitively shifting register AA right K bits at a time and comparing the 20contents of registers RAP and RA. When such contents are unequal, the shifting is stopped. Block 7505 also indicates that for each right shift of K bits the counter KA is to be incremented by 1. It is to be noted that durin~ the processing states register AA cycles upon 25 itself. Bits shifted out of the right end o~ the register enter the left end of the register through switch 7230.
Register AA has capacity for L+2 pels, where L is the length of an image line in pels. To provide for proper detection of the final run in a line when shifting right, 30 an extra set of K bits is inserted into register AA
following the end pel of a line. These K bits are made to have a different configuration from the K bits of the last pel in the line. Similarly to provide for proper detection of the first run in a line when shifting left, another set 35 of K bits is inserted into register AA prior to the beginning pel of a line. This set of K bits is made to have a different configuration from the K bi~s of the first pel in the line. ~he insertion of the extra bits is done "
- 21 - ~RANK, A~ J. 5 prior to entering the processing states. The data in register BB are constructed in a similar manner.
Upon completing the shifting and comparing operations of block 7505, register RAP generally contains 5 the last pel of the run in register AA currently being processed, and register RA contains the first pel of the next run, and counter KA contains the position number o~
the pel in register RAP. When the functions in block 7505 have been executed, STATE 2 terminates and STATE 3 lO corresponding to blocks 7510 and 7515 is entered.
Block 7510 first indicates that counter KB is to be saved in register RKB. Then register 13B is shifted right until a transition T from one level to the next occurs. This is accomplished as with register AA, by 15 repetitively shifting register BB right K bits at a time and comparing the contents of registers RBP and RB. When such contents are unequal, the shifting is stopped.
Block 7510 also indicates that for each right shift of K
bits the counter KB is to be incremented by 1. IJpon 20 completion of shi~ting, register RBP generally contains the last pel of the run in register BB currently being processed, and register RB contains the first pel of the next run, and counter KB contains the position number of the pel in register RBP. In the event that the register B13 25 run currently being processed is a head run, then the difference KB-RKB is the length of the head run. At block 7515 the contents of counter KA, the position of the register AA run currently being processed are compared to L, the number of pels in the image line~ If KA exceeds L
30 it means that all runs in register AA have already been processed, and that each remaining unprocessed run in register BB are to be treated as head runs. In this case STATE 3 is terminated, and STATE 4 is entered. If KA
equals L, then the register BB run currently being 35 processed is the last run in the image line. Elere STATE 3 is again terminated, but STATE 5 is entered. If KA is less than L, then STATE 3 is also terminated and ST~TE 6 is entered.

~ 187~Bs - 2~ -STATE 4 corresponds to blocks 7520 and 7525. Block 7520 indicates tha~ the processor develops and generates a head code and an I~ code~ The head code depends upon the length in number o~ pels o the register BB run currently being processed. The processor evaluates KB-RKB to be the length of the head run, and uses this, or a Eunction of this, as an address to access a ROM or other table memory device, which contains the specific codewords for the various head lengths. These codewords may be any conveniently chosen set of code values. In particular it is efficient to assign variable-length Huffman minimum-redundancy codes.
These codes, as well as means for addressing a table memory containing these or other codewords are discussed in my U.S~
patent, "Uniform Decoding of Minimum-Redundancy Codes,"
Serial No. 3,883,847 issued May 13, 1975. In one possible form the ROM contains a separate codeword for each distinct head length. In many situations this results in an undesirably large codebook. My above identified U.S. Patent No. 4,103,287, describes how smaller codebooks may be achieved by using a single prefix code for a range of head length values. A particular head length is then coded with a prefix code, and with an appended fixed length code which specifies a particular member within the range of values implied by the prefix code. The appended code is a simple arithmetic function of the head length and does not appear in the ROM unit. The ROM contains distinct and separate entries for only a small set of head lengths, and one or - more prefix codes, each of which applies to a range of head lengths.
Block 7520 also indicates that the processor develops and generates an ID code. This corresponds to the level of the register BB run currently being processed, and is contained in register RBP. Here also the processor uses ~he conten~s of register RBP as an address to access a ROM
or other table memory device, which contains the specific codewords for the various levels. As before it is efficient to assign Huffman codes for this purpose. As ~...... ~ .

~ ~7~5 - 23 - FR~IK, ~. J 5 mentioned previously, we may form t~o separate codebooks, one for the ID codes, and the other for the head, connect, and end codes. Also, if higher efficiency resultsl we may reverse the order o~ the H and I codes, and isolate the shead instead of the ID codes in a separate codebook. In any case, all codewords may occupy the same ROM.
At block 7525, the contents of counter KB, the position of the register BB run just processed, are compared to L, the number of pels in the image line. If Ke 10is less than L, then there are some register BB runs which have not yet been processed. In this case S~ATE 4 is terminated and STATE 3 corresponding to block 7510 is entered to shift the register BB to the next run. If KB is equal to L, then the register BB run just processed is the 5final register BB run. In this case, all of the register AA runs have also been processed, and so STATE 4 is terminated, and entry is made to STATE 18 corresponding to block 7599, where the Control 7300 of FIG. 3 is signaled to alternate switches 7210, 7220, and 7230, and to transfer 20the contents of register BB to register AA and fill register BB with a new line of image data.
STATE 5 corresponds to block 7530, where the contents of registers RAP and ~BP are compared. These registers contain the levels of the runs currently being 25processed in registers AA and BB respectively. If these levels are equal, then it is concluded in this implementation that the corresponding runs belong to the same region. In this case, exit is made from STATE 5, and entry is made to STATE 7 at block 7540 where a connect code 30is outputO As mentioned previously, particular applications may require that additional conditions be met before runs are concluded to connect. Thus, for example, it may be required that the runs overlap by at least one pel. Concomitant processing is required to handle any such 35 additional conditions. In the case that the levels of the two runs are not equal at block 7530, then the register BB
run does not connect to the register AA run. As this register AA run is the final run, there are no other 5~85 - 24 - P ~ K, A. J. 5 possible register AA runs for the register BB run to connect to, and it is concluded that the register ~B run is a head run. In this case STATE 5 is terminated and STATE 4 corresponding to block 75~0 is entered.
STATE 6 corresponds to block 7535, where the contents of registers R~P and RBP are compared. As before, these registers contain the levels of the runs currently being processed in registers AA and BB respectively. If these levels are equal, then it is concluded in this implementation that the corresponding runs belong to the same region. In this case STATE 6 is terminated and entry is made to STATE 7 corresponding to block 7540, where a connect code is output. As indicated above, additional connectivity conditions may be specified. In the case that the levels of the two runs are not equal at block 7535, then STATE 6 is terminated and STATE 8 at block 7545 is entered to perform a limited search in register AA for a run connecting to the register BB run.
STATE 7 corresponds to block 7540, which 20indicates that the processor developes and generates a connect code. This code depends upon the relative positions oE the ends of the runs currently being processed in registers AA and BB. In this particular implementation where no restriction is placed on the distance between the 25ends of the runs, there are 2L-l possibilities for the relative positions of the ends of the runs. Accordingly, in this case the processor evaluates KB-KA~L, and uses this as an address to access a ROM or other table memory. This device contains the ~L-l codewords corresponding to as many - 30possibilities for the ends of the indicated runs. As before, it is efficient to assign Huffman codes for this purpose. After the connect code is outputted, STATE 7 terminates and entry is made to STATE 14 corresponding to block 75~5, where it is de-termined if any additional 35processing of the runs in registers AA and BB is required.
STATE 8 corresponds to blocks 7545, where a search is started of subsequent runs in register AA to determine if any such run connects to the register BB run 1~5~ 5 - 25 - ~ ~ K, A. J. 5 currently being processed. In this particular implementation we include no more than two additional register AA runs in this search operation. In the material below we refer to these two runs as the first and second ssubsequent register AA runs. Other implementations may call for searching with other conditions imposed, as discussed earlier. At block 7545, the contents of registers RA and RBP are compared. Register RBP contains the level of the register BB run currently being processed.
10Register RA contains the level of the first subsequent register AA run l.e.l the next after the one tested at block 7535. If these levels are equal, then it is concluded in this implementation that the corresponding runs belong to the same region. In this case STATE 8 is 15terminated, and entry is made to STAT~ 9 corresponding to block 7550, where an end code is output for the bypassed register AA run, and a connect code is output for the two connecting runs.
STATE 9 corresponds to block 7550. Here the 20processor first develops and generates an end code. As there is only one end codeword, the processor simply accesses the appropriate location in the ROM for the code and outputs it. Then the register AA is shifted right until a transition T from one level to the next occurs, as 2sat block 7505. Block 7550 also indicates that for each right shift of K bits the counter KA is to be incremented by 1. Then the processor developes and generates a connect code, as at block 7540. STATE 9 then terminates, and entry is made to STATE 15 corresponding to block 7585.
STATE 10 corresponds to blocks 7555, and 7556.
Arrival at this state indicates that the first subsequent register AA run did not connect to the register BB run currently being processed. It is now desired to test the second subsequent register AA run, if any, for connection 35 to the register BB run. To do this, block 7555 first indicates that register AA is to be shifted right until a transistion T from one level to the next occurs, as at block 7505. Block 7555 also indicates that for each right ~ 1~756~
- 26 - ~RANK, A. J. 5 shift of K bits the counter KA is to be incremented by 1.
In the event that the first subsequent register AA run was the final run in register AA, then there is no second subsequent register AA run and the register BB run does not 5 connect to any register AA run. In this case counter KA at this point contains the value L, the number of pels in an image line. At block 7556, the contents of counter KA are compared to L. Accordingly, if KA equals L, then STATE 10 is terminated and entry is made to STATE 13 corresponding 10tO block 7570 in order to output the head and ID codes for the register BB run. If, however, KA is less than L, then STATE 10 is terminated and entry is made to STATE 11, corresponding to block 7560 in order to determine i~ the second subsequent AA run connects to the register BB run.
STATE 11 corresponds to block 7560, where the contents of registers RA and RBP are compared.
Register RBP contains the level of the register BB run currently being processed. Register RA contains the level of the second subsequent register AA run. If these levels 20are equal, then it is concluded in this implementation that the corresponding runs belong to the same region. In this case STATE 11 is terminated, and entry is made to STATE 12 corresponding to block 7565 to output the end codes for the two bypassed register AA runs, and to output the connect 25code for the connecting runs. However, if the levels are not equal then the register BB run is a head run, and STATE 11 iS terminated, and entry is made to STATE 13 at block 7570 in order to output the required head and ID
codes.
STATE 12 corresponds to block 7565. Here the processor develops and generates an end code as at block 7550. This end code is for one of the two bypassed register AA runs. Then STATE 12 iS terminated~ and entry is made to STATE 9 corresponding to block 7550 to output an 35end code for the second bypassed re~ister AA run and to output the required connect code~
STATE 13 corresponds to blocks 7570 and 7575. At block 7570, the processor develops and generates a head ~ 15~
- 27 - IlRANK, A. J. 5 code and an ID code for the register BB run, as at block 7520~ At block 7570, the con~ents of co~nter KB, the position of the register B~ run just processed, are compared to L, the numbers of pels in the image line. If 5 KB is equal to L, then the register BB run just processed is the final register B~ run. In this case STATE 13 is terminated, and entry is made to STATE 18 corresponding to block 7599, where Control 7300 is signalled to retrieve a new line of image data. If KB is less than L, then 10 STATE 13 is terminated/ and entry is made to STATE 14 corresponding to block 7580.
STATE 14 corresponds to block 7580, where register AA is shifted left until a transition T from one level to the next occurs. This is done to reverse the 15 shifting done at block 7555, and to retrieve the register AA run which was shi~ted out but not processed at that time. In accordance wi~h the left shift, counter KA
is now decremented by 1. Exit is then made from STATE 14, and entry is made to STATE 3 corresponding to block 7510, 20 in order to advance to the next register BB run.
STATE 15 corresponds to block 7585. Entry is made here after outputting a connect code. If the register BB runs just processed is the final register BB
run, then processing of the runs in registers AA and BB is 25complete, and it is desired to call in the next line of data. At block 7585, the contents of counter KB, the position of the register BB run just processed, are compared to L, the number of pels in the image line. If KB
equals L, then STATE 15 is terminated, and entry is made to 30 STATE 18 to retrieve the next line of image data. If KB is less than L, then there is at least one register BB run which has not yet been processed. In this case STATE 15 is terminated, and entry is made to STATE 16 corresponding to block 7590.
STATE 16 corresponds to block 7590. ~ere we determine if there is at least one register AA run which has not yet been processed. This is done at block 7590, where the contents of counter KA, the position of the ~ ~7~

- 28 - FI~NK, A. J. 5 register AA run just processed, are compared ta L, the number of pels in the image line. If KA is less than L, then there is at least one more register AA run to be processed. Then STATE 16 is terminated, and STATE 2 5 corresponding to block 7505 is initiated in order to advance to the next register AA run. However, if KA is equal to L, then all of the register AA runs have been processed. In this case, STATE 16 is terminated, and STATE 17 corresponding to block 7595 is activated.
STATE 17 corresponds to block 7595, which simply increases counter KA by 1, thereby causing it to be greater than L. This will force subsequent tests at block 7515 to route to block ~520. Exit is then made from 5TATE 17, and then STATE 3 corresponding to block 7510 is initiated.
15 Subsequently, the processor cycles repetitively through blocks 7510, 7515, 7520, and 7525 in order to output a head and an ID code for each remaining unprocessed register BB
run.
STATE 18 corresponds to block 7599, where the 20 control 7300 of FIG. 3 is signalled to alternate switches 7210, 7220, and 7230, and to transfer the contents of register BB to register AA and fill register BB with a new line of image data.
FIG. 5 shows one typical overall processing and 25 communications system including the coding function to be supplied in accordance with the present invention. As an illustration this system is related to two applications.
One of these concerns the automated production of the printing of advertisements in the Yellow Pages of telephone 30 directories. The other is a system for mass screening for breast cancer ~y ultrasound imaging and the associated facility for remote medical teleconsultation.
In the printing application, art copy as it typically appears in advertisements, is scanned by 35 scanner 501. Equipment such as the Scanner/Digitizer System, Model No. DSD120/240 of the Destdata Corporation, Sunnyvale, California, may be employed for this purpose.
The sampled, digitized image signals are either encoded or 1 1~7~S~

- 2~ ANK, A. J. 5 se~t directly via transmission channel 501 to graphics processor 502. These signals may represent bilevel or multilevel gray tones, colors, or texture patterns. More generally, the signals may represent any set of region 5 contents where a uni~ue number is assigned to each member of the set, and where the contents are defined parametrically, algorithmically, or by simple dictionary look-up. The signals may be generated by other processors, such as pattern recognizers, as well as by conventional 10 optical scanners. Graphics processor 502 stores these digitized images in image store 503.
Upon demand from an artist at a graphics terminal 506, processor 502 retrieves items from the image store, converts the code, if necessary, to the transmission 15 channel and/or terminal format and transmits them via transmission channel 505 to graphics terminal 5060 ~ere the advertisement layout proceeds interactively, and includes the addition of text, cropping, and size and position change of the images. A graphics terminal of this 20 nature is described by P. B. Denes and I. K. Gerschkoff in "An Interactive System for Page Layout Design", Proceedings of the ACM Annual Conference, November 1974, pp. 212-221.
Commercially available e~uipment is the AUTOLOGIC APS 22 terminal. Upon completion of an advertisement layout~
25 specification for the contents of the advertisement are transmitted back to processor 502, which stores them in an auxiliary store along with references to the coded image data in image store 503. It is possible also that new images may be generated interactively at graphics terminal 506. These would also be transmitted to ! processor 502 and coded and stored in the image store.
Upon demand from a salesman at the facsimile transceiver 508, for example, the processor retrieves an advertisement from the image store, converts the code, if 35 necessary, to the transmission channel and/or facsimile transceiver format, and transmits the advertisement via transmission channel 507 to facsimile transceiver 508. The transceiver may be located in a regional sales-office, or 1 ~75~5 - 30 - P~, A. J. 5 it may be a portable unit and carried by the salesman to the customer's site. The dex 1~ facsimile transceiver of Graphic Sciences, Inc., Danbury, Connecticut, and the digital facsimile transmitter Model DDX of the Stewart-sWarner Corporation, Chicago, Illinois are among the equipments that may be used for these purposes. The facsimile copy is presented for customer approval. Changes may be marked on the facsimile copy, and transmitted back to graphics processor 502, for routing to a graphics lOterminal for immediate or subsequent action by the interactive artist.
When a directory is to be published, processor 502 retrieves the image data from image store 503, converts the code, if necessary, to that 15required by the printing composition equipment. It then marries tbe image data Eor each a~vertisement with the text and other data carried in an au~iliary store, and transmits the entirety of data to the local utilization device 504, in this case a printing composer. Such composition 20 equipment may be, for example the Mergenthaler Linotron(t~c~ k) photocomposer with film output. Laser plate-making devices are also potential local utilization devices.
In the above system, the present invention finds important application to reduce storage requirements, to 25 reduce transmission bandwidth, and to decrease transmission time. With respect to storage, the large volume of images appearing in the advertisements of a telephone Yellow Pa~es~
directory, as well as the high resolutions, on the order sf 500 to 1000 lines per inch required for printing purposes, 30 results in an extremely large data base. A system of this type is viable only if the data is coded efficiently to minimize storage requirements. It is well known, of course, that images innately require greater transmission bandwidth than voice or other types of data, and that data 35 reduction for this purpose is desirable. However, in thi~
application transmission time is of even higher priority in order to mee~ real-time, on-site customer demand, and also efficiently to utilize manpower at the graphics terminal.

1 ~7~6~

- 31 - ~RAN~, ~. J. s For these reasons the present invention may be incorporated both at the central graphics processor sitel an~ also at any interface with a transmission channel, most importantly in this application at the facsimile transceiver and at the 5graphics terminal, and possibly also at the scanner.
ficient storage and transmission of images are also of key importance in the second application of mass screening for breast cancer by ultrasound imaging. The coding efficiencies obtainable with the present invention 10are re!ported in "Coding Vltrasound Images," by A. J. Frank and J. M. Schilling, Proceedings IE~E 1977 Workshop on Picture Data Description and Management, April 1977, pp. 172-181. In this case, the proposed system operates as follows. Scanner 500 is an ultrasound transducer fitted into a local traveling field unit. The signals generated are sampled, digitized, coded according to the present invention, and transmitted to graphics processor 502, located at a central hospital. Processor 502 stores the images in image store 503. Upon demand, these coded images 20may be called out of the image store 503, decoded, and transmitted to local utilization device 504 for high quality hardcopy output on film or photographic paper. The Photomation P1700/of Optro~nics ~nternational, Inc., Chelmsford, Massachusetts, or similar equipment may serve 25 as the output device. In addition, images in the image store may be retrieved, decoded, and submi-tted to an automatic pattern recognition system. Finally, the images may be transmitted as part of a teleconsultation operation via transmission channel 504 to graphics terminal 506, or 3D via transmission channel 507 to facsimile transceiver 508.
Such teleconsultation operations are expected to provide important specialist services to small hospitals or paramedics in outlying areas. In this case, graphics processor 502 would be located in the outlying area, and 35 the graphics terminal and facsimile equipment in the larger central city medical facility. Experiments with teleconsultation operations are reported in "An Evaluation of the Teleconsultation System Elements," by S. Krainin, - 32 - FRANK, A. 1. 5 et. al., Massachusetts General Hospital, Report P~-242 584 prepared for the Veterans Administration, June 1975. With mass screening efforts, the potential si~e of the image store is enormous. Furthermore, it is expected that a smammogram requires long term storage of about five years.
In addition, a woman suspected of having a cancer will be advised to have multiple subsequent scans, all of which are to be stored, and compared with each other by automatic or visual means. Accordingly, efficient coding is a 1~necessity, particularly for storage purposes and for transmission from local field scanners 500 to graphics processor 502. While the expected volume of consultation traffic is unknown at present, it is probable that the viewers at the graphics terminal and facsimile receivers 15Will be highly trained medical staf~ working under pressure, and thereby also requiring speedy transmission.
As before, the present invention finds important application at the graphics processor site, and also at scanner 500 for encoding, and at the graphics terminal 506 20and facsimile device 508 for decoding.
It is to be noted that the two-line at a time operation of the present invention is particularly well suited for the line-by-line mode of operation usually ound in facsimile devices, graphics terminals, and scanners.
25 The present invention is ~lso compatible wi-th digital networks concepts. Furthermore, the relative simplicity of logic of the present invention permits the implementation by use of hardwired logic components, LSI circuits, or microprocessors. The latter is particularly attractive for 30 the central graphics processor, where versatility as well as speed is desirable. An application of a commercially available microprocessor ~or communications purposes is described in "Microprocessor Implementation of High-Speed Data Modems," by P. J. Van Gerwen~ N. A. M. Verhoeckx, 35 H. A. Van Essen, and F. A. M. Snijders, IEEE Transactions on Communications, Vol. COM-25, No. 2, February 1977, pp. 238-250.
In accordance with the aspects discussed above, ~ 1575~5 - 33 - F~Kt A. J. S
Listings 1, 2, and 3, attached as appendices hereto, represent an implementation of the coding logic of the present invention in a program suitable for microprocessor operation. The coding in all listings is in the FORTRAN
programming language, as described, for example in the Honeywell Series 60 ~Level 66)/6000 FORTRAN manual, Honeywell Information Systems, Inc., Waltham, Massachusetts, 1976. This particular language may be replaced by any other language depending upon availability, l0desired operating speed, economics, or other pertinent processing considerations.
Listing 1 contains the main multilevel processing program. The techniques used are those enumerated in FIG~ 4B, where block numbers correspond to program statement numbers in Listing 1 with minor differences as indicated below. Shift registers AA and BB in FIG. 4B
correspond to the arrays LINEA and LINEB in Listing 1. In addition to the processing of the image lines contained in LINEA and LINEB, this program also supplies the function of 20transferring LINEB to LINEA and reading in the next image line into LINEB. In the encoding process, this program assigns various codes to the image parameters. These codes vary in size but are assumed in this implementation individually not to exceed the processor word sizeO For 25each co~e, this program calls the subroutine OUTPUT, comprising ~isting 2. The arguments passed to the subroutine OUTPUT are the code itself at the right end of one computer word, and the length of the code in bits in another computer word. The subroutine OUTPUT then appends 3~the indicated code bits to an internal buffer. When this buffer is full, OUTPUT writes the buffer contents into an auxiliary store, and continues to fill the bufer starting again at the beginning. At the end of processing an image, the main program calls OUTPUT a final time to cause it to 35 flush any partially filled buffer. The subroutine CUTPUT
in turn calls upon two bit manipulation routines, called JGETB and JPUTB, contained in Listing 3.
For ease of presentation, the program in 1 ~7~

- 34 - ~K, A. J. S
Listiny l is constrained to handle image lines of length lO, only 5 connect codes, lO head codes, and 8 region identification codes. The restriction on 5 connect codes is obtained by limiting connecting veins to be within S 2 pels o~ each other. Tests to invoke this restriction are added at blocks ?545 and 7560. In order to test for this properly, the progression to the next AA run indicated at block 7550 in FIG. 4~ is done instead at 7545. This then requires that AA be retrogressed 2 runs at block 7580.
The codewords and codeword lengths in bits are contained in the codebooks specified in the DATA statements at the beginning of the program. The arrays KODEC and KBITC contain the codewords, and the codeword lengths in bits, respectively, for the 5 connect codes. The arrays 15 KODEH and KBITH contain this information for the head codes. The arrays KODEI and KBITI contain this information for the region ID codes. The variables KODEE and KBITE
contain this information for the single end code. The codewords are in octal form, and the codeword lengths are 20 in decimal form. For example, the code for a head of length l pel is contained in the first member of the array KODE~1. This has the value of octal~000~0~0074. The corresponding first member of KBITH is 6, which tells us that the codeword is 6 bits long. The codeword then is 25 octal 74, or binary llllOO. For a connect where the LINEB
run is two to the left of the LINEA run, the index into the codebook is computed to be KB-KA ~ MAXDIF + l, where MAXDIF
is the maximum allowable distance in pels between the two runs. In this case, then the index is l. Entering the 30 array KODEC with index l yields the value of octal00~0000~0000. The corresponding first member of KBITC
is l, indicating that the codeword is l bit long. The codeword then is simply G.
~he set of codewords in Listing l are ~uffman 35 minimum-redundancy codewords. Any o-ther set of variable or fixed length codewords apply equally well. In addition, although the number of codewords and the image line length are restricted in the sample programr the present invention ~ ~5'~S5 - 35 - ~RANK, A. J 5 bears no such limitation. It is apparent to any one skilled in the art that the image line length and the codebooks may be increased to any amount within the storage capacity of the processor by changing the array dimensions 5 in the DIMENSION statement, and the declared line length L, and the codebook definition in the DATA sta-tements.
Decoding of the encoded data and reyeneration of the levels corresponding to the original digitized form of the image proceeds as a reverse process to the encoding ess described above. In particular where variable length codes are used, the passing and decoding of a bit stream consisting of such codes may be accomplished by the decoding system disclosed in my aforementioned U. S. Patent No. 3,883,847.

~ 1~7565 - 3G - FRANK, A. J. 5 APPE,~JDICES
Ll ~;TI ~G
c MULTILl:V~t. ~)~?OC~SSING PRO~I?AI~l C ' . ..
DIMENSIOI`l LINEA~12) ,LI;`1E~ ) ,I(ODF:C~5) ,KODE~!llV), .
~ODEI (8) ,K13ITC ~51 ,KBIT~I (lQ) ,K~ITI (8;
` .

c CODE~OOKS:
C . ' " ' DAT~ KoD~c/o~ 000a~J0000~ ,O~1~00~ 00B14 ,O0'./~
o~ 0~ 34,0s~0~0~a~3s 2 KI~ITC/l ~4 /4 ,5,5/
DAT~ KoDEHJo~tl0c1~0~J00074~o000~l9~10q~0l7;~o~3~ 3~3~lJ~
' ' oa~0~ 0~l74 ,0~0~ 0l75 ,0~
i . 2 O~J00~10~1774,00~0~ 0775,0~3~0c~7/~, 3 OÇ~0~0~10~777/, 4 K8.IT~6,7,7,7,7,7,9,9,~,9/
DATA KO,~EI/O~0~ 0,0~0q~ J~ U~,O~?'~' l O000g0a000~24,0000000a00i~.5,0000'~u~?~b 2 000~00~0~076,0~00~0~77/, 3 K~ITI/l,2,3,5,5,5,6,6/
DATA KODE~/OM00'3~0000002/, KBITE/2/
~TA 1/10/,LINE/0/

c INITI.~LIZ~:.

Ll-L~i .. . .. . ~

~ 1~7~65 L'~=L+~ .FXANX, A. J. 5 M~XDIF=~
C : .
c R~AD NEXT I~A,E LINE; INSERT TRANSITION P~L.S ~r STA~T
c AND E~ OFF LINE; IF FI~STT LINE, CODE .~LL ~U~S A~ H~AU~: ..

1~ READ ~9,END=9~99)(LINE~(I),I=Z,I.l) ~ !
LXNE~(l)=LINE~(2)+1 . '.
LI~EB(L2)=LINE~LI)+l IF(LINE-GT.O) GO T~ 755 LIME=l c PROCESS FI~ST IMAGE LINE:
C
c RA=L+l KB=O

c PROCESS LI,~ES A ~N~ B
C
75~1 KA=O ' K~=O
75~5 K~=KA+l IF(LI~EA~KA~.E~.LI~EA~ A+l)GO TO 75 751~ KBR=K~
7511 KB=KB+l IF(LINE~tKB`).F,Q.LINE~K~l) GO TO 7511 7515 IF(KA.EQ.L) G~-TO 7S3~

. ... _ . _ . . . ., . . . . _ . _ . . . . .. _ _ . _ . _ .. _ _, . . _ _ _ . _ . -- _ w _ .

~ ~756~
(. ( _ 3~ _ PR~NKj ~. J. 5 IF(KA.t,~'.L) GO T~ 753S
?52~ LEN=K~-~BR
C~LL OUTPUT(R~ITtl(LE~,KODE~l~LEN)) L~V=LINE~(~B)~l ..
CALL OUTPUT(K~ITI(LF.V),KODEI(LEV~) 7525 IF~K~.LT.L) GO TO 7Sl~ .
~0 ~0 75~9 . .
753~ IF(LI~E~(RA.~E.LIN~B(KR)) GO TO 752 GO TO 754~
7535 IF~LINEA~KA.NE.LINE~(KB)) GO TO 7545 7540 NDEX=K~ +MAXIF+l CALL OUTp~T(KBITc~NnE~)~KoDEx~NDEx)) , 7545 KA=KA~l IF(LINEA(K~).EO.LINE~(KA~l)) GO TO 7545 IFtLI~1E~(KA).~..LINEB(KB)) GO TO 7555 IF~IABS(K~,KB).GT.2) GO TO 7555 ~ .
755~ CALL OUTPUT~KBITF"KOD~E) NDEX~-KB-KA+~AXDIF+l C~L~ OUl'PUT~K~ITC(NDEX),KODr:C~NDEX)) - 7555 RA=KA~l IF(LINEA(KA).EQ.LINEA(KA~ ) GO TO 7555 7556 IF~A.GT.L) GO TO 757 7560 IF~LINEA(KA).NF..~INE~(KB)) GO TO 757 IFIIA~S(KA,KB3.GT.2~ GO TO 7570 7565 CALL OUTPUT(K~ITE,KODFE) GO TO 755~J -. ~

57~
757g LE~ K[~-KBR - 3? - FR~NK, A. J. 5 CJ~LI, OUl'PUT(KBITH ~LE:NJ ,KODE~l (LEtJ) ) LEV=LII~ B) tl CA1L OUTPUT~KBITI ~LEV) ,~ODEI (LEV) ~ . ..
7575 IF~KB.EQ.1.) GO TO 7S99 ` .
758~ DO 7S82 I~=l, 2 , ` .
758l ~ CA-l 7582 IF(l.I~IEA(KA~EQ.LI~`JEA~K~l)) GO TO 758l GO TO 751~ .
7585 IF(KE!.EC?.L) GO TO 7599 . .
759~ IF(~CA.I.T.L) GO TO 7505 `
7595 X~=KA~l ', C .' ' , ~ : `' .
c ~;TART OF r~w LINE, MOVE LINE E3 TO LINE A: .
C - . .
7599 DO 76~) N=l,L2 . .
760~ LINEA tN) =LINEE~ (N) (;0 TO 10 'c c FINAL CALL TO SUBROUTINE OUTPUT TO Fl,USH BUFFE~:
C
., , .l 9 9 9 3 CALL OUTPUT ~ 3 7, O) . I -STOP
EI~D

'` ( I ~575~ ( - O - ~RANK, A. J, 5 I,ISTI ~IG 2 . C OUTPUT SUBROUTI~lE
SIIB ROUTI NE OUTPUT ( N, JWORD) C
C T}IIS 5UBROUTINE MOVES THE N RIG~ IOST BITS OF THE WORD JW::~RD TO ~HE
C BUFFER IB~F. EACH TIr~l~ IBUF IS FILLED IT IS OUTPUTTEI:). N>36 CAUSE
C ~HE UNFILLED PORTION OF IBUF ~O BE FII,LE~D WITH ZERO~S P.NI) OUI~PU~EL
DI:~IE~;ISION X BUP ( 1001 . .. .
D~TA Iy' l~,IBUFSZ~l 00~, IZERO~0~,N~ITS~36~ .
DATh NBUFJ'0~ .
C NBITS lS MACHINE r~ORD SIZE
C
C TEST FOB FINAL CALL:
C ~ . I
IF (N,. GE. 37) GO TO 20 -N2=N
C
C TEST IF INPUT BIT~ EXCEED BUFFER ..
C
ITBIYS=NBITS*IBUFSZ~1 .
~LEFT=ITBITS-I .
JWORD2=JWORD
IF~N.LE.NLEFT) GO TO 10 C . . .
C INPUT BITS EXCEED BUFFER. BRE~K B~TS INTC T~O PART5.
C EXTR~CT INITIAL NUMBER O~ BITS AND PUT AT END OF CURRENT BUFFE~ LG~
C, N2=NLEFT .
K=NBlTS~ l-tl - .
J~ORD2=JGETBtJWORD,K,NL~FT) 10 CALL JPUTB.(IBVF,I,N2,JWOnD2) ~ 2 -IF~I.LT.ITBITS) RETURN
C
C WRITE OUT FULL ~UFFER ~ . j C . I
WRITE (09) IBllF
NBUF=NBUF~
I=l .
IF ~N. EQ . ~12) RETURN
C
C PUT FINAL NUMBER OF BITS AT START OF NEX~ BUFFER LOAD.
C
N2=~1- NLEFT
CALL JPUTB ( IBUF, I, N2 ~ JWORD) I=I t N2 RETURN
C ' . ~-C THIS IS FINAL CALL; F~USH BUFFER, IF NECESSARY.
20 IF(I~EQo 1) GO TO 50 ~ ~ ~575~ ~
C - '11 - FRANK, A. J. 5 C FILL CUI~RENT hlOE~D WIT~I %EE~OES .
C
L= ~ NBI T5 ~1 1~5=I,~Bl:TS-It 1 CAI.L JPUTB (IBUF~I ~M~IZERO) IF ~L. EQ. IE~UFSZ) GO TO 40 C

C FILL REST OF E~UE`E'EEl WITH ZEROES ..
C

L= L~ 1 DO 30 J=Lo I BUFSZ
30 IBUF ~J)l~O .
C , . . ..
C ~RITE OUT BUFFE;R AND END OF FILE MARK
c . !
40 ~1RITE (09) IEIUF
NBUF-NBUF~ I

RETUE~ N
E

..
. ' -i ~

75~$
- ~ - 42 - FRAhK, l\. ~1. 5 LIsTI NG _ 3 This is a listing of the FORTnAN routines ~GE.TB ar~d JPUTB which use only ~he functions klOVEL (shift left), MOVER (shift right logi-~al~, and OEl.

C JG~B RETRIE~'ES SPECIFIED BITS
FUNCTIO~I JG~TB(STRIN~,I,N) C ROUTINE VSES ~IOVE~ AND MOVEL FUNCTIONS WHICH SHIFT T~lE. 1.
C BITS~IN A WO~D RIGHT A~D LEFT.
C ST~ING IS BIT STRING.
C I IS ST~RTI~G BIT OF DESIRED STRING~ !
C N IS LENGTH OF DESIRED BIT STRING. .
C ,, INTEGER STRING~1),Q,R,N,~10RK,OR - -C HONEYWELL 6000 HAS 36 BITS~10RD
DATA ~36~ . ¦
Q = ~I-1)fW
R = MOD(~
IWORD = Q~1 IF ~R~N.GT.W) GO TO 10 C ALL BITS IN SAME WORD
~70RK = MOVEL~STRING~IWORD),R) ~ ¦
JGET~ = MOVER(WORK,W-N) RETURN
C BITS SPAN A WORD BOUNDARY
i 10 ~1 = W-R
112 - N~
WO~K = MO~L(STRING(IWORD),R) JGETB = MOVER(WORK,r~-N~
IWORD = I~ORD~
5~0RK - MO~E~(STRING~IWORD),~-N2 JGETB =,OR~JGETB,WORK) RLTV~N
END

.
C JPUTB REPLACES BITS ~N STRING
SUBROUTIN~ JpurB (STRING~ I,N,PUT) C ROUTINE USES MOVE~ AND t~lOVEL FUNCTIONS WHIC~ SHIFT T~E
C BITS IN A ~ORD RIGHT ~ND LEFT.
C STRI~G IS BIT STRINGo C I IS STARTING BIT OF STRING TO REPLACE.
C N IS LENiGT~ OF STRING TO REPLACEo C ~IGHTMOST N BITS OF P~T ARE USED AS REPL~CEMENT.
INTEiSE~ STRING(1)~PUT,Q,R,PUT2,WORKfORii,TAIL,W
C HO~EYWELL 6000 HAS 36 BIT~WOXD
~TA W~36~
Q = ~ W
Il = MOD S (I~
IWORD = Q~ 1 .
.

~ 15~S
- 4 3 - FI~NKJ ~\. J. S
IF ~N4~.GT.w) GO TO 10 C ~LL BITS IN SAME WORD
C CLEA R UPP EE~ El I TS OF PUT
PUT2 ~ MOVEL ( PUT, W-NI
PUT~ = MOVi~R ~PUT2,W-N) , C GET TE~AILING ~3ITS IN ~ORD, ShVE
TAIL = ~lOVEL(STRING~IWORD) ,R+N) ..
TAIL = ~lOV~R ~TAII., R~N) WOR X = t~:OVE R ( ST R I NG 1 X WOR D ), h-- R) WORK = ~OVEL(WORK~N) WORK = OR lWORK, PUT2~
WORK = MOVEL IWORK,W-N-R) ST~ ING ( IWCRD) = OR (WORK, TA IL) P~ETURN

10 N1 = W-R .
N2 = N-~t C ~ORK WITH FIRST WORD
PUT2 = MOVE:L 5PUT~,W-W) .
PUT2 = MOVER(PUT2rW~N1) WORK = MOVER(STRIWG(IWORD),N1) ~ORK = MO~JF.L ~WORK, N1 ) STRING (IWCRD~ = OR (WORK, PUT2) C NOW NEXT WORD
IWORD = IWORD~ 1 `
PUT2 = MOVEL~PUT,~N2) . .
WORK = MOVEL ~ STR ING ( IWORD), ~2) WOB.K = MOt7ER ~WORK, N2 STRING (IWCIRD) = OR (WORK" eUT2) RETUE~N
END

.

, ' .

~ . t

Claims (4)

Claims:

1. Apparatus for coding a two-dimensional inform-ation field having a plurality of regions, each region having one of a plurality of different graphical values, comprising scanning means for determining, on a path by path scan across said field, the graphic value of successive pels along each of said paths, storage means for simultaneously storing the graphic values so determined for two successive path scans across said field, and means for comparing the stored graphic values of pels from one of said scanned paths with those from the other of said paths, and including means, utilizing the stored values and the results of said comparison, for generating:
for each scanned region:
(a) a first binary electric code representative of the length of a constant-value run along a scanning path;
(b) a second binary electric code representative of the graphical value of said region, and (c) a third binary electric code representative of the end of the last scanning path scanning said region; and for any scanning path, a fourth binary electric code representative of the connectivity of a constant-value run along said path to a constant-value run along a previous scanning path.

2. Apparatus according to claim 1 wherein said means for comparing includes shift register means for comparing the binary bit positions of said binary electric code representations of like-valued runs on two successive scan paths.

3. Apparatus according to claim 2 further comprising means for defining new regions which are fragments of other regions, and means for encoding said new regions in the same manner as other regions.

4. A method for coding a two-dimensional information field having a plurality of regions, each region having one of a plurality of different graphical values, comprising determining, on a path by path scan across said field, the graphic value of successive pels along each of said paths, simultaneously storing the graphic values so determined for two successive path scans across said field, comparing the stored graphic values of pels from one of said scanned paths with those from the other of said paths, and, utilizing the stored values and the results of said comparison, generating:
for each scanned region:
(a) a first binary electric code represent- ative of the length of a constant-value run along a scanning path;
(b) a second binary electric code representative of the graphical value of said region, and (c) a third binary electric code representative of the end of the last scanning path scanning said region, and for any scanning path, a fourth binary electric code representative of the connectivity of a constant-value run along said path to a constant-value run along a previous scanning path.