Analyzing system and method

Abstract: A symbol analyzing system processes spectral power data of an input test symbol for deriving line width and line count information about the symbol, and for generating a reliability confidence factor for each line count. An exclusion controller progressively reduces the spectral power by progressively excluding a larger portion of the upper frequency end of the power spectrum. The excluded power levels are compared to a set of predetermined reference power levels from an ideal reference symbol. Each excluded power level that compares with a reference level is matched with reference coefficients Kw and Kc for that reference level. Each matched excluded power level has a remaining non-excluded power level Pbw in the non-excluded bandwidth BW at the lower end of the frequency spectrum. These included power levels and bandwidths are matched with the reference coefficients. The line width LW and line count LC of the input test symbol are calculated based on the included power levels Pbw, the included bandwidth BW, and the coefficients Kw and Kc.

Description: TECHNICAL FIELD This invention relates to symbol analyzing systems used in character recognition, and more particularly to symbol analyzing systems which produce character confidence factors generated by a multiple analyzing sequences based on progressively excluded data. BACKGROUND Heretofore symbol recognition systems processed all of the data presented without data exclusion, and the character was either recognized or not recognized. The recognition sequence was a single processing step in which the input symbol data was compared with a reference library of possible symbols. The result of the comparison was either pass or fail without any provision for reliability weighting with confidence factors. US 4,817,176 issued March 28, 1989 to Marshall et al, discloses such a prior art pattern recognition technique. An article by Anothai. Rattarangsi and Roland T. Chin published in the Proceedings 10th International Conference on Pattern Recognition, Atlantic City, USA, June 16 - 21, 1990 and entitled "Scale-Based Detection of Corners of Planar Curves" discloses another pattern recognition system. It is therefore a concern of this invention to provide an improved symbol analyzing system for deriving feature information about the input symbols. It is another concern of this invention to provide such a symbol analyzing system which provides a confidence factor indicating the reliability of the feature information. In accordance with a first aspect of the present invention there is provided a symbol analysis system as set out in claim 1. From a second aspect the present invention provides a method of analysing symbols as set out in claim 37. 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 block diagram of a symbol analyzing system showing the data exclusion feature; FIGURE 2 is a block diagram of the data exclusion and feature calculation portion of a symbol analyzing system; FIGURE 3A is a block diagram of the data exclusion controller of Figure 2; FIGURE 3B is a graph of power "Pf" at each frequency of the power spectrum verses frequency "Fr" of a typical input test symbol; and FIGURE 3C is a graph of normalized partial power "nPpart" of the excluded upper portion of the power spectrum verses the "BW" of the included portion of the power spectrum of Figure 3B. The elements of the invention are designated by two digit reference numerals. The first digit indicates the Figure in which that element is first disclosed or is primarily described. The second digit indicates like features and structures throughout the Figures. Some reference numerals are followed by a letter which indicates a sub-portion or feature of that element. GENERAL EMBODIMENT - BLOCK DIAGRAM (Figure 1) Optically visible symbols printed or otherwise embodied on a tangible medium such as document 10D are digitized by a suitable reading device such as optical scanner 10S, and stored in memory 10M as a document bit map. Preferably the document to be digitized is uniformly illuminated by a scanning light source for providing reflected light which is intensity modulated by the presence and absence of the lines forming each symbol. In this disclosure, the term "lines" shall mean the linear and/or curved strokes or graphic elements forming the symbol including elements that extend horizontally, vertically and at various angles. The modulated reflected light is detected by a suitable photo-sensitive device such as an array of photodiodes which provide a stream of diode pulses to the document bit map. For maximum line position resolution, there is a pixel stored in the bit map for each diode pulse. Retrieval controller 10R identifies bit maps for individual test symbols (character cells 10c) within the document bit map using segmentation techniques based on the continuous blank background region between successive lines of text and separating adjacent symbols. The bits within the "test" cell selected for analysis are retrieved by data passes along cell rows "R" and/or cell columns "C" by the retrieval controller. The each row generally corresponds to horizonal pass across the symbol, and each column generally corresponds to a vertical pass across the symbol. The retrieval controller systematically addresses the cell memory, forming a binary bit stream of "1"s and "0"s. Each edge boundary between symbol area and background region within the test symbol bit map causes a corresponding edge transition in the bit stream. The leading edge of each symbol area in each retrieval pass changes the binary state of the bit stream from the background region state to the symbol area state. The trailing edges change the binary state back to the background state. In a conventional white document with black print, the white background region from the margin of the cell to the edge of the symbol is one binary state ("0" for example). The black symbol area between the leading edge and the trailing edge of each symbol area is the other binary state ("1" for example). Spectral transform device 12 transforms the bit stream of each cell retrieval pass across the test symbol into a spectrum response of amplitude verses frequency containing symbol feature information such as line width "LW" and line count "LC". The transform employed by spectral transform device may be any suitable mathematical transform such as a Fourier transform, a Hadamard transform, a Karhunen-Loeve, a sine transform, a cosine transform, and Haar transform, and others. Further information concerning suitable mathematical transforms may be found in the text "Application of Digital Processing", section 4.3, written by Alen V. Oppenheim (of MIT), and published by Prentice-Hall, Inc; or in the text "Digital Picture Processing", 2nd edition Volume 1, section 5.3, written by Azriel Rosenfeld (of University or Md) and Avinash C. Kak (of Purdue), and published by Academic Press, Inc. The spectral response of the retrieval pass currently being retrieved is processed by data exclusion controller and calculator 14. The resulting feature information is entered into the first location of feature entry table 16F as D-1. The spectral response is then reduced by a predetermined data increment producing modified feature information which is entered into the second location of the feature entry table as D-2. The response is reduced by another increment and entered into the third location. Each cycle of the data exclusion sequence generates a feature information entry by progressively reducing the bandwidth "BW" of the spectral response with corresponding exclusion of a progressively larger portion of the upper frequency end of the spectral response. The data exclusion sequence is terminated at the nth data level (the nth cycle) and the last retrieval pass is entered into the nth location. At the end of the data exclusion sequence, feature entry table 16F contains a set of N entries for a the current row or column retrieval pass of cell 10C. Entry Processor 16P statistically treats the N data exclusion entries generated by the N exclusion cycles, using mathematical techniques to merge them into a single composite entry for the current retrieval pass from character cell 10C. The processor then generates an accompanying confidence factor for the current composite entry. The next retrieval pass from cell 10C is transformed by spectral transform device 12 into a spectral response, which produces the next N entries and the next composite entry. The composite entry and confidence factor of each pass of the R rows and C columns are entered into composite table 18C for further processing by suitable matching device 18M against a library of reference symbols contained in library memory 18L. The library contains predetermined feature information such as LWs and LCs for reference symbols in an ideal reference font derived from data retrieval passes across the rows and columns of a pre-existing bit map of each reference symbol. The matching device may be a suitable LW and LC comparing system such as a set of matched filters or a neural algorithm matching network. The reference LW and LC feature information for each reference symbol is pre-entered into the matched filters, and the test LW and LC feature information for each test symbol is advanced through the filters. US 4,817,176 issued March 28, 1989 to Marshall et al, shows a Fourier spectrum approach in which the input data is compared with standard known characters to obtain a "best match". The Marshall patent is hereby incorporated by reference in its entirety into this disclosure. POWER EXCLUSION EMBODIMENT - (Figure 2) Cell memory 20C containing a bit map of the test symbol selected for analysis provides a bit stream into Fourier transform device 22F for each retrieval pass of the rows and columns in memory 20C. The bit stream includes greyscale data GS for preserving the intensity characteristics of the original document such as black/white contrast and tonal shades. The output of the Fourier transform device is a series of complex numbers (a+bj); one number for each frequency. Each number has a real component "a" containing the line width (LW) and line count (LC) information, and an imaginary component "bj" containing the line position information. The series of "a" and "b" values are store in Fourier memory 22M along with the retrieval pass number "N" of the row or column. The format of the Fourier transformation provides a Fourier frequency and memory location for each bit in the row or column of the current retrieval pass. The number of locations "F" generated by the Fourier transformation is a power of two (F = 2 n ), and may exceed the number of bits retrieved. The second half of the Fourier spectrum is a redundant mirror image of the first half. The number of usable or non-redundant frequencies in the Fourier spectral response is therefore F/2, extending from F1 up to Fmax. Power conversion device 23P converts the series of "F" complex numbers in the Fourier response of the current retrieval pass into a corresponding series of real numbers "Pf" of a power spectral response extending from F1 up to Fmax (see Figure 3B) in accordance with the relationship: Power = Fourier 2 Pf = a 2 + bj 2 in which Pf is the power contained in the power spectral response at a particular frequency. The resulting F/2 real Pf numbers are stored in power memory 23M. Power exclusion controller 24 reduces the power spectral response of the current retrieval pass to an optimum initial level by eliminating frequencies of the power spectrum starting with the highest frequency Fmax. The initial power reduction eliminates the high frequency portion from Fmax down to Fi (see Figure 3B) which contains low amplitude, high frequency noise caused by non-symbol system artifacts such as tiny ink spots, dust and sensor apparitions. The LW and LC feature information is contained in the low frequency portion of the spectral response and is not affected by this initial power exclusion. Line width calculator 25W calculates the test symbol line width LW along the current retrieval pass at the initial power level (and subsequent levels) in accordance with the relationship: LW = BW x Kw in which LW is the calculated line width of the test symbol along the current pass (the average width of all symbol areas traversed during the current retrieval pass across the character cell), and BW is the bandwidth of the power spectrum Fi down to F1 remaining after each cycle of the exclusion sequence eliminating the upper frequencies Fmax down to Fi (see Figure 3B), and Kw is a constant for each power level obtained from the power exclusion controller (see Figure 3A). The line width of the symbol is the largest feature within the cell bit map and is therefore confined to the lower frequency portion of the spectral response. The calculated LW is entered into the first location of line feature entry table 26F. Line count calculator 25C calculates the test symbol line count LC along the current retrieval pass for the initial power level in accordance with the relationship: LC = Pbw x Kc / LW in which LC is the calculated line count of the test symbol along the current pass (an estimate of the number of symbol areas traversed during the current retrieval pass across the character cell), and Pbw is the power remaining within the bandwidth BW of the power spectrum Fi down to F1 after each cycle of the exclusion sequence eliminating the upper frequencies Fmax down to Fi (see Figure 3B), and Kc is a constant for each power exclusion level obtained from the power exclusion controller (see Figure 3A). LCs are typically five or less and also confined to the lower frequency portion of the spectral response. The calculated LC is entered into the first location of table 26F along with the calculated LW. The level of the power spectrum is further reduced by a predetermined power increment. An LW and LC are calculated for the reduced level and entered into the second location of the line feature entry table. The power is reduced by another increment and entered into the third location. The data exclusion entries are generated by progressively excluding a small power increment with progressive loss of high frequencies in the power spectral data. The power exclusion sequence is terminated at an optimum final power level and the last entry is entered into the last location. Line width merger 26W merges all of the LWs in table 26F into a single:line width for the current retrieval pass by determining the mean line width (LWm). The mean value of the line width is a decimal number forming a composite of all of the LWs generated by the power exclusion sequence for the current retrieval pass. Similarly, line count merger 26C merges all of the LCs in table 26F to determine the mean line count (LCm). The mean value of the line count is rounded off to the nearest whole integer by round-off device 26R to provide "LCr". Confidence factor generator 26CF receives "LCm" for the current retrieval pass from LC merger 26C and the LC exclusion entries from table 26F, and generates the standard deviation (SD) and the confidence factor (CF) of the exclusion entries. The standard deviation for the current retrieval pass is the square root of the sum of the squares of the individual deviations from the LCm value defined by the relationship: Standard Deviation = 1stDev 2 + 2ndDev 2 . . + NthDev 2 The confidence factor "Cf" for the current retrieval pass is defined by the relationship: Cf = (LCm - SD) / LCm, and indicates the reliability of the line feature information. The LWm and LCr and CF resulting from the retrieval passes of each of the R rows and C columns of the test symbol, are entered into a composite table for further processing through a match device and character library. POWER EXCLUSION CONTROLLER 24 - (Figure 3 ABC) Power exclusion controller 24 receives frequency Fr and power Pf data from power memory table 23M, and provides a bandwidth BW, and a bandwidth power Pbw, and Kw and Kc coefficients from bandwidth table 34BW for each retrieval pass. The bandwidth data and coefficients are used in LW calculator 25W and LC calculator 25C. Power integrator 34P within controller 24 provides the total integral "Ptot" of Pf with respect to frequency over the entire power frequency spectrum (Fmax down to F1): in which Pf is the power at a given frequency, Fmax is the highest frequency in the entire power spectrum, and F1 is the lowest frequency in the entire power spectrum. Total power Ptot is the total area under the power spectrum response curve (see Figure 3B - bold curve) across the entire spectrum Fmax to F1. The integrator also provides a series of partial of indefinite integrals "Ppart" of Pf with respect to frequency over the range of excluded upper frequencies (Fmax down to Fi): in which Pf is the power at a given frequency, Fmax is the highest frequency in the partial power spectrum, and Fi is the lowest frequency in the partial power spectrum which defines the portion of the upper frequencies to be excluded. Partial power Ppart is the partial area under the power spectrum response curve (see Figure 3B) across the upper portion of the spectrum Fmax to Fi. Pbw calculator 34B within controller 24 calculates the power Pbw remaining in the non-excluded bandwidth portion of the spectral response after each exclusion cycle in accordance with the relationship: Pbw = Ptot - Ppart. Each Pbw is stored in a test power memory table 34T along with the associated bandwidth BW (frequency Fi down to F1). Normalizer 34N within controller 24 divides each of the Ppart integrals by the total Ptot integral to provide normalized excluded power integral "nPpart" in accordance with the relationship: nPpart = Ppart / Ptot. The normalized power nPpart is a unitless number between 0 and 1, stored in test power table 34T along with the associated Pbw and BW. The nPpart numbers in memory 34T are test power ratios for each frequency of the current retrieval pass of the test symbol. Reference power ratio table 34R within controller 24 contains a set of predetermined power ratios "nPref" and associated Kw and Kc coefficients for a suitable ideal reference such as the power spectrum of a single line reference symbol - the function Sin(x)/x (see Figure 3B - light curve). The reference power ratios correspond to predetermined power exclusion levels of the reference symbol. Comparator 34C within controller 24 receives the lowest nPref ratio from table 34R for comparison to the lowest nPpart ratios from test table 34T starting with Fmax. When a compare occurs, comparator 34C pairs the bandwidth BW and bandwidth power Pbw of the nPpart with the coefficients Kw and Kc of the nPref for storage in bandwidth table 34BW for use in line width calculator 25W and line count calculator 25C. SPECIFIC EMBODIMENT The following particulars of symbol analyzing are given as an illustrative example of data exclusion sequence. In this example: The digitizer has 400 photodiodes per inch formed in a printed circuit. The number of rows R in the character cell is 50 and the number or columns C is 100. The number of frequencies F in the Fourier transform is 64 for row passes (32 non-redundant frequencies) and 128 for column passes (64 non-redundant frequencies). Greyscale data GS is 256 bits. The initial optimum power level Pbw at the start of the exclusion sequence is about a 90% of the total power Ptot. The initial excluded power Ppart is about 10% of Ptot. The initial Fi is about 10. The exclusion sequence includes eight incremental cycles each of which excludes about 5% of Ptot from the Pbw. The final optimum power of Pbw is about 50% of the Ptot. The final Fi is about 5. The values given above are not intended as defining the limitations of the invention. Numerous other applications and configurations are possible. CONCLUSION It will be apparent to those skilled in the art that the objects of this invention have been achieved as described hereinbefore by providing an improved symbol analyzing system for deriving line width and line count feature information about the input symbols. Clearly various changes may be made in the structure and embodiments shown herein without departing from the concept of the invention. Further, features of the embodiments shown in the various Figures may be employed with the embodiments of the other Figures. Therefore, the scope of the invention is to be determined by the terminology of the following claims and the legal equivalents thereof. It will thus be immediately apparent from the foregoing that some aspects of the invention are as follows. In a first aspect, the invention consists in the realisation that the width of a line present in an image is manifested by the bandwidth (or, viewed in a different way, the upper frequency end of the bandwidth) of spatial frequencies present; a narrow line will produce a broader band of spatial frequencies than a broad line (the power of which is concentrated in lower spatial frequencies). Further, the number of lines present in a given spatial area of the image is, for a given bandwidth (and hence line width) in direct relation to the power within that bandwidth. Thus, the larger the number of lines, the more power within the bandwidth (and hence vice versa). It is of considerable value in character or other pattern recognition to be able to derive the width of lines and the number of lines in the character, and the invention provides a method of doing so. Viewed in a second aspect, the invention consists in the method of performing a spatial transformation on an image signal, so as to derive spectral magnitude versus frequency information, and then deriving the spectral bandwidth at a number of spaced spectral magnitude levels; the variability in data derived from the spectral bandwidth provides a good measure of the reliability of the data for recognition. However, it would be realised that the above aspects are not exhaustive and there are other equally valid explanations of the effect of the invention in symbol, character or other recognition. Although in the above the Fourier transform is given as an example, it will be recognised that as stated above any other type of spectral spatial transform would be applicable; the transformer could be two-dimensional rather than performed line by line as described above. Equally, the power spectrum could be found by methods such as auto correlation or even time domain filtering, although this is not preferred. Many other novel and inventive aspects of the foregoing description will be apparent to the skilled reader, and each is considered independently and separately inventive.

Claims: A symbol analysis system which receives and processes symbol data for deriving feature information concerning the symbols represented by the symbol data; document memory means (10M) for receiving and storing an input bit stream as a document bit map; retrieval means (10R) for identifying symbol bit maps within the document bit map and systematically addressing selected symbol bit maps to provide bit streams of symbol data; spectral transform means (12,22F) for transforming the bit streams of symbol data from a symbol bit map into a spectral response, and characterised in that it further comprises: data exclusion means (14,24) for receiving the spectral response and progressively reducing the bandwidth of the spectral response by excluding a progressively larger portion of the upper frequency end of the spectral response; and processor means (16P,26F) for matching power values indicative of the reductions in power of the bandwidth limited spectrum with reference values to generate a set of symbol feature in entries for the symbol bit map and forming a single composite entry for the symbol feature, and generating a confidence factor indicating the reliability of said composite entry. A system according to claim 1, wherein the spectral transform means provides a Fourier spectral response. A system according to claim 2, wherein the Fourier spectral response extends from a maximum frequency Fmax at the upper end of the spectral response to a fundamental frequency F1 at the lower end of the spectral response. A system according to any one of the preceding claims further comprising digitizer means (10S) which provides greyscale data within the symbol data which is included in the spectral response from the spectral transform means. A system according to any one of the preceding claims, wherein the symbol feature information derived by the system is line width and/or line count information. A system according to any one of the preceding claims and further comprising a symbol bit map memory means for receiving the symbol data for the selected symbols from the document memory means. A system according to claim 6, wherein the symbol data in the symbol bit map memory means is arranged by rows of bits and columns of bits. A system according to claim 7, wherein the retrieval passes along the symbol bit maps are along the rows and/or columns of the symbol bit map. A system according to claim 8, wherein the retrieval passes along the rows of bits in the symbol bit map generally correspond to horizontal passes across the symbol, and the retrieval passes along the columns of bits in the symbol bit map generally correspond to vertical passes across the symbol. A system according to any one of the preceding claims, further comprising a power conversion means (23P) for converting the Fourier spectral response into a power spectral response. A system according to claim 10, wherein said set of symbol feature information is line feature information. A system according to claim 11, further comprising line width calculator means (25W) responsive to the set of line feature information for calculating a corresponding set of line width LW entries. A system according to claim 12, further comprising line width merge means (26W) for merging the set of LW entries into a single merged line width LWm. A system according to any one of claims 11 to 13, further comprising line count calculator means (25C) responsive to the set of line feature information and to the set of LW entries for calculating a corresponding set of line count LC entries. A system according to claim 14, further comprising line count merge means (26C) for merging the set of LC entries into a single merged line count LCm. A system according to any one of claims 12 to 15, wherein the merged line width LWm is the mean value of the set of line width LW entries. A system according to any one of claims 14 to 16, wherein the merged line count LCm is the mean value of the set of line count LC entries. A system according to claim 17, further comprising line count round off means (26R) for rounding off the LCm to the nearest whole integer to provide a rounded off line count LCr. A system according to claim 17 or claim 18, and including confidence factor generator means responsive to the set of LC entries from the LC calculator means and to the LCm from the LC merge means for generating a confiderce factor CF, in accordance with the relationship: CF = (LCm - SD) / LCm in which SD is the standard deviation between the LCs in the set of line count entries LC and the means line count LCm. A system according to claim 19, and including a feature entry table (26F) which receives and stores the set of LW and LC entries. A system according to any one of claims 9 to 20, wherein the power spectral data of the input symbols includes greyscale data. A system according to any one of claims 9 to 21, wherein the power spectral data is a power level Pf at each frequency Fr within the spectrum of power frequencies. A system according to any one of claims 9 to 22, wherein the exclusion means further comprises an integrator means for providing the integral of power with respect to frequency. A system according to claim 23, wherein the integrator means provides the integral total of power Ptot over the entire spectrum of power frequencies in accordance with the relationship: in which Pf is the power at a given frequency, Fmax is the highest frequency in the entire power spectrum, and F1 is the lowest frequency in the entire power spectrum. A system according to claim 24, wherein the integrator means also provides the integral of partial power Ppart over the upper part of the frequency spectrum to be excluded in accordance with the relationship: in which Pf is the power at a given frequency, Fmax is the highest frequency in the partial power spectrum, and Fi is the lowest frequency in the partial power spectrum which defines the portion of the upper frequencies to be excluded. A system according to claim 25, wherein the exclusion means further comprises a bandwidth power calculator means for providing the bandwidth power Pbw of the lower portion of the power spectral data to be included in the series of line information in accordance with the relationship: Pbw = Ptot - Ppart. A system according to claim 26, wherein the exclusion means further comprises a normalizer means for providing a normalized power ratio nPpart in accordance with the relationship: nPpart = Ppart / Ptot. A system according to claim 27, further comprising a test table means for receiving and storing the series of Pbws from the bandwidth power calculator means and the series of nPparts from the normalizer means. A system according to any one of claims 9 to 28, further comprising a reference table means for storing a set of predetermined reference normalized power ratios nPref from a predetermined reference symbol. A system according to claim 29, wherein the predetermined reference symbol is an ideal symbol having a predetermined line width and line count. A system according to claim 29, wherein the predetermined reference symbol is an ideal symbol having a predetermined line width and a line count of one and is represented by the relationship ¦Sin(X) / X¦. A system according to any one of claims 29 to 31, wherein the reference table means further stores a set of line width coefficients Kw and a set of line count coefficients Kc, one for each nPref ratio. A system according to claim 32, further comprising a comparing means for comparing the nPpart ratios from the test table means starting with the lowest with the nPref ratios from the reference table means starting with lowest to match Kw and Kc coefficients with BWs and Pbws. A system according to claim 33, wherein the line width calculator means provides a calculated line width in accordance with the relationship LW = BW x Kw in which BW is a bandwidth from the test table means, and Kw is a line width coefficient from the reference table means. A system according to claim 34, wherein the line count calculator means provides a calculated line count in accordance with the relationship LC = Pbw x Kc / LW in which Pbw is a bandwidth power from the test table means, and Kc is a line count coefficient from the reference table means. A system according to any one of claims 33 to 35, further comprising a bandwidth table means for storing a set of coefficients from the reference table means and the matched BWs and Pbws from the test table means. A method of analysing symbols comprising storing an input bit stream representing a plurality of symbols as a document bit map, identifying and retrieving symbol bit maps from the document bit map and systematically addressing selected symbol bit maps to provide bit streams of symbol data, transforming a bit stream of symbol data from a symbol bit map into a spectral response, and characterised in that the method further comprises receiving the spectral response and progressively reducing the bandwidth of the spectral response by excluding a progressively larger portion of the upper frequency end of the spectral response, matching power values indicative of the reduction in power of the bandwidth limited spectrum with reference values to generate a set of symbol feature information entries for the symbol bit map and processing the set of symbol feature information entries to form a single composite entry for the symbol feature and generate a confidence factor for the composite entry. A method according to claim 37, wherein a bit stream of symbol data is generated by retrieval passes through the symbol bit map, and further providing the power spectrum for each retrieval pass across the symbol bit map; integrating the power with respect to frequency to provide of the total power Ptot over the entire power spectrum of power frequencies in accordance with the relationship: in which Pf is the power at a given frequency, Fmax is the highest frequency in the power spectrum, and F1 is the lowest frequency in the entire power spectrum; progressively reducing the power spectrum by excluding a progressively larger portion of the upper frequencies thereof; integrating the progressively larger excluded portion of the power spectrum with respect to frequency to provide a series of partial power integrals Ppart over the upper part of the frequency spectrum in accordance with the relationship: in which Pf is the power at a given frequency, Fmax is the highest frequency in the power spectrum, and Fi is the lowest frequency in the partial power spectrum which defines the portion of the upper frequencies to be excluded; subtracting each of the excluded Ppart from the Ptot to provide a series of bandwidth powers Pbw for a series of bandwidths of the lower portion of the power spectrum to be included in deriving the line information; providing a set of predetermined reference powers and reference coefficients from a predetermined reference symbol; and comparing the excluded Ppart powers starting with the lowest with the reference powers starting with lowest to match the set of reference coefficients with a corresponding set of included Pbws and bandwidths for each retrieval pass. A method according to claim 38, further comprising the step of dividing each of the excluded Ppart by the Ptot to provide a series of normalized power ratios nPpart for comparison with the set of normalized reference power ratios. A method according to claim 39, in which the step of progressively reducing the power level further comprises the initial step of establishing an optimum initial level by eliminating the highest frequencies of the high 'frequency portion of the power spectrum. A method according to either of claims 39 or 40, wherein the reference coefficients are line width coefficients and line count coefficients. A method according to claim 41, further comprising the step of calculating a line width LW and a line count LC in accordance with the relationships: LW = BW x Kw LC = Pbw x Kc / LW in which BW is a bandwidth from the test table means, and Kw is a line width coefficient from the reference table means Pbw is a bandwidth power from the test table means, and Kc is a line count coefficient from the reference table means.

Inventors: MELEN ROGER D, MELEN, ROGER D., Melen, Roger D., c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: G06K9
IPC codes: G06K9