Data format for recording digital data and method

Abstract: A two dimensional row and column based system for storing digital data is formatted on a suitable base medium such as paper sheet 10. The data format on the sheet includes at least one digital data storage area 10A formatted along row axis 10R and a column axis 10C. A suitable deposited recording material such as ink entries 12 is carried by the sheet for recording the digital data. The data format is formed by a plurality of data units 1OU having L data entry locations 14. The data is contained in the selective presence or absence of the recording ink within the locations. Each data unit extends R locations along the row axis and C locations along the column axis. Any E entry locations of the L locations within the data unit are designated recording material present locations. The L-E remainder locations are designated recording material absent locations. The number of codes C that may be represented by these E in L type data units is determined by the relationship: C = (L!)/(L-E)!(E!). The number of entries E is the same for each data unit throughout the data storage area, and cannot be less than E.

Description: This invention relates to the writing and reading of data, and is particularly but not exclusively concerned with recording digital data on a paper medium. Digital data has been recorded as punched holes in a paper medium in the form of paper tape and IBM cards. The hole entries were necessarily large resulting in a very low density data format. Digital data has also been recorded on paper medium by the conventional printing of ink pigments. The pigment entries were typically black and somewhat smaller then the punched holes, producing a somewhat higher density format. Laser beam printing on paper offers a higher density format. Current printer have an ink dot density of 300 dot per inch (dpi) with a dot diameter of about 3 mils (0,076 mm). However peripheral dispersion of the particles of toner dust limits the closeness of adjacent entries in the data format. High density dots with toner dispersion may introduce read errors when the digital data is retrieved. In addition, the toner dots may be out of registration or irregular in shape further limiting the recording density. European Patent Specification No. EP-A-0,299,383 discloses identification code sheets and a method for reading such sheets in which sixteen or more sub-areas in a code-bearing representation area are grouped in four or more assemblies carrying representations of binary signals. United States Patent Specification No. US-A-4,114,033 discloses a machine readable bar code information card on which bar codes have been recorded in dual directions so that information can be encoded according to the "2 OUT OF 7 COMBINATION". European Patent Specification No. EP-A-0,147,090 discloses a high density code for coded optical recording of binary data in which an "empty" symbol position is added between symbols in a TOEP code. None of these prior disclosures are concerned with providing a solution to the problem of reducing read errors caused by, for example, toner dispersion, lack of registration or irregularity of shape of recording dots representing encoded information. In accordance with a first aspect of the present invention there is provided a method of recording data in coded form as set out in claim 1. In accordance with a second aspect of the present invention there is provided data handling apparatus as set out in claim 10. In accordance with a third aspect of the present invention there is provided a method of reading digital data as set out in claim 13. In order that the present invention may be more readily understood, embodiments thereof will now be described by way of example and with reference to the accompanying drawings, in which: FIGURE 1 is a diagram of a base medium containing a plurality of data units; FIGURE 2A is a fragmentary view of a 4 entries in 8 locations embodiment arranged in a single row 8 columns wide; FIGURE 2B is a fragmentary view of a 4 in 8 embodiment arranged in two rows each 4 columns wide; FIGURE 2C is a fragmentary view of a 4 in 9 embodiment arranged in 3 rows each 3 columns wide; FIGURE 3 is a diagram of a single data unit showing toner intrusion between adjacent locations; FIGURE 4A - 4F show a various codes represented by the 4 entries in 8 locations data format; FIGURE 5 is a diagram of a document containing printed text with the corresponding data codes printed in the corner; and Figure 6 shows schematically printing and reading apparatus according to the present invention The first digit of each reference numeral in the above Figures indicates the Figure in which that element is shown. The second digit indicates like structural elements, and the final letter indicates a sub-portion of an element. Referring now to Figure 1 of the drawings this shows a two dimensional row and column based system for storing digital data is formatted on a suitable base medium such as paper sheet 10. The data format on the sheet includes at least one digital data storage area 10A formatted along row axis 10R and a column axis 10C. A suitable deposited recording material such as ink entries 12 is carried by the sheet for recording the digital data. The data format is formed by a plurality of data units 10U having L data entry locations or cells 14. The data is contained in the selective presence or absence of the recording ink within the locations. Each data unit extends R locations along the row axis and C locations along the column axis. Any E entry locations of the L locations within the data unit are designated recording material present locations. The L-E remainder locations are designated recording material absent locations. The number of possible codes C that may be represented by these E in L type data units is determined by the relationship: N = (L!) / (L-E)!(E!) where N is the total number of possible codes represented by the data format, L is the number of data locations within a single data unit, and E is the number of locations within each data unit which actually contain entries. The number of entries E is the same for each data unit throughout the data storage area. CODE EMBODIMENTS (Figures 2A, 2B and 2C) The number of codes represented by a particular E in L data format depends on the number of locations available and the number of entries permitted. The embodiment of Figure 2A shows data unit 20A with E = 4 entries in L = 8 locations arranged in one row (R = 1, C = 8). The embodiment of Figure 2B shows data unit 20B with two rows each having L/2 = 4 locations (R = 2, C = 4). The above 4 entries in 8 locations embodiments having 70 possible codes calculated as follows: N = (L!) / (L-E)!(E!) = (8!) / (8-4)! (4!) = 70 The fractional term (L!)/(L-E)! yields the number of ways 4 entries of recording material may be entered into 8 locations. In the 4 of 8 embodiments the fractional term is 8x7x6x5 = 1,680. The denominator term (N!) = 4x3x2x1 = 24 eliminates the redundant codes from the fractional term. The resulting 70 codes are order insensitive entry patterns, each forming a unique arrangement of entries and empty locations usable for storing digital data. In general the number of codes contained in a data format system is maximum for the case E = L/2. The following Code Table A of the 4 in 8 embodiment (see Figures 2A and 2B) shows that the more codes are available when E = L/2 = 4. Entries E and Number of Codes for L = 8, E = 0 through 8 Number of Entries E 0 1 2 3 4 5 6 7 8 Number of Codes N 1 8 28 56 70 56 28 8 1 Remainders L-E 8 7 6 5 4 3 2 1 0 The number of Codes represent by the various E cases is symmetrical about the center peak value because of the equivalence between the entries E and the non-entry remainders L-E. As shown in the bottom line of Code Table A, each case for E is equivalent to the corresponding L-E case. That is, E = 3 in L = 8 has 56 codes, and L-3 = 5 in L = 8 also has 56 codes. This equivalence symmetry is also true for odd values of L such as data unit 20C (see Figure 2C) with 9 locations arranged in 3 rows and 3 columns, as shown in the following Code Table B. Entries E and Number of Codes for L = 9, E = 0 through 9 No of Entries E 0 1 2 3 4 5 6 7 8 9 No of Codes N 1 9 36 64 126 126 64 36 9 1 Remainders L-E 9 8 7 6 5 4 3 2 1 0 The number of codes peak for the case E = (L-1)/2 = 4 and the parity case E = (L+1)/2 = 5. The E = 4 embodiment (see Figure 2A), consumes 20% less toner and offers four fewer intrusion interfaces (see Figure 3). More codes may be obtained by increasing the number of locations L in the data format as shown in Code Table C for L = 16. Entries E and Number of Codes for L = 16, E = 0 through 16 Entries 0 2 4 6 8 10 12 14 16 Number of Codes 1 120 1820 8008 12870 8008 1820 120 1 L-E 16 14 12 10 8 6 4 2 0 Increasing the E in L data format from 4 in 8 (Code Table A) to 8 in 16 (Code Table C) doubled the base area required to carry the data, but increased the number of codes available by a factor of 12870/70 = 183.8. However the larger number of codes requires larger processing memories and a longer processing time. BASE MEDIUM 10 Base medium may 10 be any suitable sheet like structure with sufficient body to retain the recording material in position within the data format. The base medium may be a synthetic substance such as mylar (or other plastics) or the base medium may be a natural cellulose substance such as paper. Some plastic bases may be reused by washing off the recording material with a solvent. RECORDING MATERIAL 12 Recording material 12 may be any suitable powder or liquid such as toner material which may be deposited on the recording medium, and which contrasts with the base medium. Both powder and liquid toner material may be deposited with sufficient accuracy by conventional laser printers and ink jet printers. During scanning to retrieve the data, the dark toner absorbs most of the incident,scanning photons resulting in a high greyscale value. The dark or black greyscale GS b of the "near black" toner approaches a theoretical greyscale limit 100% which is never obtained due to residual reflection of the toner. The exposed paper is light and reflects most of the photons resulting in a low greyscale value. The light or white GS w of the "near white" paper approaches theoretical limit of 0% which is never obtained due to residual absorbtion of the paper. The surface roughness of the paper scatters some of the incident light adding to the value of GS w . The signal-to-noise ratio of the scanning system is defined by the relative greyscales of the near black and near white locations: S/N = (contrast signal) / (background noise) S/N = (GS b - GS w ) / Maximum [S.D(GS b ), S.D.(GS w )] where S.D.(GS b ) is the standard deviation of the values of the GS b entries throughout the system, and S.D.(Gs w ) is the standard deviation of the values of the GS w entries. In a high data density embodiment, each toner entry may be a single dot formed by many smaller toner particles. Lower density embodiments, may have entries formed by a collection of dots such as 2x2 or 3x3. The GS b of the dot collection is an average of all of the dots in the collection, and will have small greyscale deviations then the single dot embodiment. The toner may be a black carbon based material or a colored based material. A plurality of pigmented toners having colors such as red, yellow, and green may be employed in a single system. The color of each entry is as significant as the location of the entry within the data unit. The number of codes that may be represented by a color based E in L data unit is determined by the relationship: N = 2 P (L!) / (L-E)!(E!) where P is the number of pigments or colors employed. A 3 color 4 in 8 data unit has 8x70 = 560 available codes. Toner color systems formed by primary colors present many color schemes for supporting a vast number of codes. METHOD OF RETRIEVING The method of reading digital data stored in an E in L type data unit involves scanning the data unit, ordering the scanned data by greyscale, and selecting the E locations with the highest greyscale as the E designated present locations. The scanning is accomplished by a suitable photon sensing arrangement such as a wide spectrum light source with an LED detector array. The resulting stream of L data signals is modulated in response to the amount of deposited recording material in each of the L locations. The modulation of the signals are compared to determine the order of the signals from most modulation to least modulation. The E most modulated signals are selected as the E entries. These signals correspond to the E locations with the most deposited recording material. In a light/dark embodiment, the base medium is light (white paper) and generally reflective to the scanning photons, and the recording material is dark (black toner) and generally non-reflective to the scanning photons. The modulations provided during the scanning step are greyscale modulations produced by the difference in reflectivity of the locations. The E locations with the highest greyscale (toned locations) may be selected, or the L-E locations with the lowest greyscale (non-toned) may be selected. The selection process is non-parametric. The value of the greyscales are not measured or compared to a threshold reference value, but merely ordered within the group of L signals. TONER INTRUSION - (Fig 3) High data densities require small locations, and the toner from a toned location may intrude over a location interface into an adjacent location. If the adjacent location receiving the intruding toner is another toned location (black), the intrusion is harmless. However if the adjacent location is designated as a toner absent location (white), the presence of the intruding toner will darken the adjacent light location from a low greyscale value (near 100% white) to a higher greyscale value. Toner intrusion across this present/absent interface reduces the signal to noise ratio. Ideal toner entry 32I (see Figure 3) is a perfectly round dot formed of infinitely tiny toner particles, and centered in square location 34I with a well defined periphery. Toner entry 32I does not intrude on any of the adjacent locations, even though the entry fills the location touching the interface sides 36I of the location. Maximum theoretical dark greyscale GS b max is 78.5%, and occurs when the diameter of the entry dot equals the side dimension of the square location. Each of the four white corners of the location occupy about 5.6% of the area of the location. The maximum greyscale condition produces potential zones of intrusion along the middle portion of the interfaces where the circle entry in-tangent to the side of the location. Misshapen toner entry 32M in location 34M, however is not ideal but is considerably out-of-round due to timing and optical imperfections. A portion of the misshapen entry intrudes across interface 36M into adjacent white location 34W. This intrusion both lowers the greyscale value for toned location 34M from the maximum value of 78.5%, and increases the greyscale for white location 34W from a near zero value. This unfortunate adjustment in greyscale decreases the signal to noise ratio of the digital data. Displaced toner entry 32D in location 34D, is also not ideal. The displaced entry is below the center of the location due to registration imperfections. A portion of the displaced entry intrudes across interface 36D into adjacent white location 34W which further decreases the signal to noise. Fuzzy toner entry 32F in location 34F, does not have a well defined periphery due to the statistical spread of parameters values in the printing process. Dispersion of the toner ink particles produces a larger dot with progressively decreasing toner concentration from center of the entry to the periphery. Toner particles from the fuzzy entry intrudes across interface 36F into adjacent white location 34W. Intrusion from the adjacent black locations due to entry shape, placement and dispersion (and other causes such finite size toner particles) increases the light greyscale GS w of white location 34W. This degradation may result in white location 34W having a higher greyscale value then greyscale of one of the toned locations in the same data unit causing a read error. Guard band 20G (see Figure 2B) around each data unit prevents toner intrusion from black locations in the adjacent data units. The toner dots may be smaller than the square locations containing the dots in order to reduce the intrusion into the adjacent locations. Figure 2A shows a toner dot with a diameter of about 0.7 the length of the side of the square location. FIGURE OF RELIABILITY Codes with many B/W (black to white) intrusion interfaces have a lower reliability than codes with fewer B/W interfaces. On the other hand like to like interfaces B/B (black to black) and W/W (white to white) offer no possibility of intrusion and tend to improve the reliability. The Figure of Reliability (FR) for codes in general is: FR = (B/B + W/W) / (B/W) where B/B is the number of black to black interfaces in the code, W/W is the number of white to white interfaces in the code, and B/W is the number of black to white interfaces in the code. The less unreliable codes may be discarded to improve the overall reliability of the data format, or assigned to special functions. In the guard band embodiment (see Figure 2B) the 12 exterior interfaces (Ext) are protected from intrusion by toner from adjacent data units by guard band 20G. Only the 10 interior interfaces must be considered. For the guard band embodiment, the FR becomes: FR = (B/B + W/W + EXT) / (B/W) where EXT is the number of external interfaces protected by a guard band. The FRs for the 4 in 8 codes (with 2 rows and 4 columns) are shown in Figures 4A - 4F and calculated in Table D below: Figure of Reliability With Guard Band (E=4, L=8, R=2, C=4) Fig 4A FR = (0 + 0 + 12) / 10 = 6/5 = 1.20 Fig 4B FR = (1 + 1 + 12) / 8 = 7/4 = 1.75 Fig 4C FR = (2 + 2 + 12) / 6 = 8/3 = 2.66 Fig 4D FR = (2 + 2 + 12) / 6 = 8/3 = 2.66 Fig 4E FR = (3 + 3 + 12) / 4 = 9/2 = 4.50 Fig 4F FR = (4 + 4 + 12) / 2 = 10 = 10.00 The FRs vary from a low value of 1 (no B/B or W/W) to a high value of 9 (maximum B/B and W/W with minimum B/W). In the same six codes without the guard band, the 12 exterior interfaces may,be treated as one half L/L (like to like) either B/B or W/W, and one half B/Wext, based on a 50% black and 50% white distribution of entries in the adjacent data units. For the non-guard band embodiment, the FR becomes: FR = (B/B + W/W + L/L) / (B/Wint + B/Wext) where L/L is the total number of black to black plus white to white interfaces around the exterior of the data unit, B/Wint is the number of black to white interfaces inside the data unit, and B/Wext is the number of black to white interfaces around exterior of the data unit. The FRs for the guard band embodiment are calculated in Table E-below: Figure of Reliability Non Guard Band (E=4, L=8, R=2, C=4) Fig 4A FR = (0 + 0 + 6) / (10 + 6) = 3/8 = .375 Fig 4B FR = (1 + 1 + 6) / (8 + 6) = 4/7 = .572 Fig 4C FR = (2 + 2 + 6) / (6 + 6) = 5/6 = .833 Fig 4D FR = (2 + 2 + 6) / (6 + 6) = 5/6 = .833 Fig 4E FR = (3 + 3 + 6) / (4 + 6) = 6/5 = 1.200 Fig 4F FR = (4 + 4 + 6) / (2 + 6) = 7/4 = 1.750 The FRs for the non guard band embodiment are much lower than the guard band embodiment due to the intrusion of toner from adjacent data units. CODE/TEXT EMBODIMENT (Figure 5) The digital data contained in the codes may be any type of information including control software, identification matter, and alpha-numeric codes such as ASCII. Document 50 containing eye readable printed text 58T (see Figure 5) occupying a major portion of the document, may have the corresponding ASCII codes 58C printed on the same document occupying a minor portion thereof. The storage site for the code may be positioned in the margin out of the normal text area. The text/code embodiment of Figure 5 shows code sites in the lower lefthand corner and in the upper righthand corner of the document away from punch holes 50P, staples 50S, and dog eared wear 50D in the lower righthand corner. These corner positions permit the code site to be scanned for code retrieval without removing the document from the binder or book holding a set of documents together. Eight bit ASCII code has 256 possible codes which could be converted into an E in L data format having an equal (or greater) number of codes. Alternatively, the most reliable 64 codes of the 70 codes provided by the 4 in 8 data format may be employed to represent each six byte segment of the 8 bit ASCII code data stream. The 2,000 maximum character capacity of a conventional 8 1/2 by 11 inch sheet has 16,000 conventional binary bytes requiring 2,666 of the 4 in 8 data units. At a dot density of 300 dpi, only a fragment of a square inch is required to hold the 2,000 ASCII codes. The numbers and dimensions given above are not intended as defining the limitations of the invention. Numerous other applications and configurations are possible. Referring now to Figure 6 this shows schematically writing and reading apparatus according to an embodiment of the present invention. Thus in Figure 6 there is shown a stream of input data 68-I which is to be processed for printing in the E entries in L locations data format which has previously been described, then scanned, and finally returned to an output data stream 68-0. Error correction insertion at step 100 converts the input data steam into the E in L format, and introduces the data redundancy required for the desired level of error correction using Reed-Solomon codes. Injection framing at step 101 provides two dimensional alignment marks (XY) and organizes the E in L data on the page to be printed in order to accommodate the later scanning step. Line rastering presents at step 102 the E in L data to the printer 68-P in line by line sequence. Printer 68-P may be any suitable printing device such as a Canon laser printer model LBP8-III for placing the ink particles onto recording material 60 to form toner entries 62. The steps 100, 101 and 102 can be under the control of a suitable microprocessor unit 103 so as to present the data in the required format for printer 68-P. Alternatively the central processor unit of the printer 68-P could be suitably programmed. Scanner 68-S may be any suitable scanning device such as a Canon optical scanner model IXF 30 for providing toner present and toner absent signals. Post scan skew alignment and contrast adjustment at steps 104 and 105 compensate for the printer skew and contrast. Extraction framing at step 106 reorganizes the two dimensional data format for serial transmission as output data stream 68-0. Error recovery corrects any noise errors introduced by the printing and scanning; and impairment errors caused by storing and handling the recording medium. As in the printing sequence the data recovery steps 104 to 106 may be under the control of a microprocessor unit 107 or the scanner 68-S may be suitably programmed. It will be appreciated that the coding system just described provides an improved data format system for recording digital data which can have a high data density and yet can be read reliably. The data format described is non-parametric and additionally error prone codes can be discarded and eye readable text can be printed on the same document as encoded data.

Claims: A method of recording data in coded form on a recording medium comprising generating on the recording medium a two-coordinate array of machine readable data units (10U), each data unit defining a coded character and having L locations (14) each of which can contain a data cell, the locations of each unit being provided by R locations extending along a row axis and C locations extending along a column axis, and in which E locations of each data unit are designated recording material present locations so that L-E locations of each data unit represent recording material absent locations, E being an integer greater than 0 but less than L, so that the total number of codes possible is N = (L!)/(L-E)!(E!), and in which a present/absent interface is formed in any data unit when a recording material present location is adjacent to a recording material absent location, and characterised in that a plurality of codes are discarded and in that the number C of characters which can be represented by a data unit is determined by the relationship N' = (L!)/(L-E)!(E!) - (number of the discarded codes), the discarded codes having the most present/absent interfaces (B/W) between adjacent locations (14). A method according to claim 1, wherein L is an even number and E = L/2, or L is an odd number and E = (L-1)/2 or (L+1)/2. A method according to either of the preceding claims, wherein the number of locations in the column axis in a data unit C = 4, the number of locations in the row axis is R = 2, E = 4. A method according to any one of the preceding claims, further comprising providing inter-unit guard margins between adjacent data units, the inter-unit guard margins being designated as recording material absent areas (206). A method according to claim 4, wherein the inter-unit guard margins either extend along the row axis between adjacent data units or along the row axis and along the column axis between adjacent data units. A method according to any preceding claim, wherein the recording medium is paper, and the recording material is a generally non-reflective toner substance deposited as a single round dot of toner in each designated recording material present location, and wherein the locations for receiving the round toner dots are square. A method according to claim 6, wherein the paper also contains alpha-numeric text in readable form. A method according to claim 6 or claim 7, wherein the diameter of the round toner dot is shorter in length to the length of the side of the square location. A method according to claim 8, wherein said diameter is approximately 0.7 times the length of said side. Data handling apparatus comprising: means (100, 103) for receiving a data stream representing a plurality of characters; means (101, 102, 103) for converting each character of the data stream into coded format; and means (68-P) for recording the coded data onto a recording medium so that the characters are stored in a two-coordinate array of machine-readable data units, each data unit having L data locations with R locations extending along the row axis and C locations extending along the column axis of the array, each location being capable of containing a data cell in the form of recording material, such a location being defined as a recording material present location, and wherein in each data unit E locations are recording material present locations, and L-E locations are recording material absent locations with a present/absent interface being formed in a data unit when a recording material present location is adjacent a recording material absent location; and characterised in that the number N' of characters which can be represented by a data unit is determined by N' = (L!)/(L-E)!(E!) - (number of discarded codes) the discarded codes having the most present/absent interfaces between adjacent locations. Apparatus according to claim 10, wherein said recording apparatus is adapted to deposit a round dot of toner in locations designated as data present locations. Apparatus according to claim 10 or claim 11, wherein L is an even number and E = L/2 or L is an odd number and E = (L-1)/2 or (L+1)/2. A method of reading digital data stored in a two dimensional format on a base medium by the selective presence and absence of deposited recording material within a plurality of two dimensional data units having L data locations any E locations of which are designated recording material present locations and L-E locations of which are designated recording material absent locations a present/absent interface being formed in a data unit when a recording material present location is adjacent a recording material absent location, and in which each stored data unit is a character represented by the recording material present locations, and the number of characters N' = (L!)/(L-E)!(E!) (number of discarded codes), where the discarded codes have the most present/absent interfaces between adjacent locations, the method comprising the steps of: scanning the data units with photons to provide a stream of data signals which are modulated in response to the amount of deposited recording material in each location; determining the order of the signals based on the degree of modulation; selecting the E most modulated signals from each data unit which correspond to the E locations in the data unit with the most deposited recording material. A method according to claim 13, wherein base medium is generally reflective to the scanning photons and the deposited recording material is generally non-reflective to the scanning photons, and the modulations provided during the scanning step are greyscale modulations produced by the difference in reflectivity of the locations. A method according to claim 14, wherein during the selection step, the E locations with the highest greyscale are selected.

Inventors: HUGHES-HARTOGS DIRK, HUGHES-HARTOGS, DIRK, Hughes-Hartogs, Dirk, c/o Canon Research Center
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G06K15
IPC codes: G06K19, G06K7, G06K1, G09C5