Standard No.:	GB/T 23704-2017
English Name:	Two-dimensional bar code symbol print quality test
Chinese Name:	二维条码符号印制质量的检验
Chinese Classification:	L71    Code, character set and character recognition
Professional Classification:	GB    National Standard
Issued by:	AQSIQ; SAC
Issued on:	2017-12-29
Implemented on:	2018-7-1
Status:	valid
Superseding:	GB/T 23704-2009 Information technology - Automatic identification and data capture techniques - Bar code print quality test specification - Two-dimensional symbols
Language:	English
File Format:	PDF
Word Count:	22500 words
Price(USD):	670.0
Delivery:	via email in 1 business day

Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative. This standard is developed in accordance with the rules given in GB/T 1.1-2009. This standard replaces GB/T 23704-2009 Information technology - Automatic identification and data capture techniques - Bar code print quality test specification - Two-dimensional symbols, and the following main changes have been made with respect to GB/T 23704-2009: ——The standard name is changed to Two-dimensional bar code symbol print quality test; ——ISO/IEC 19762, GB/T 18284, GB/T 21049, GB/T 35402, ISO/IEC 16022, ISO/IEC 16023 and ISO/IEC 24778 are added (see Clause 2); ——The term and definition of "reflectance margin" is added (see 3.12); ——The symbol grade is obtained through one scanning measurement, and does not requires five scans (see 7.4); ——The definitions of "contrast uniformity" and "reflectance margin" parameters are added, and the concepts of "module MOD", "codeword MOD", "symbol MOD", "module RM", "codeword RM" and "symbol RM" are added (see 7.8.4); ——The requirement "the interim codeword grade of each parameter for each codeword is the highest codeword grade for that parameter obtained for all scans of that codeword." is modified to "the interim codeword grade of each parameter for each codeword is the highest codeword grade for that parameter obtained on any scan for that codeword.” (see 6.2.5); ——The proprietary parameters of each symbology for symbol classification related to Data Matrix code and QR Code are not detailed, and only the symbology standards containing these parameters are given (see Annex D); ——The quality parameters of "reflectance margin", "format information" and "version information" are added (see Annex G). This standard has been redrafted and modified in relation to ISO/IEC 15415:2011 Information technology - Automatic identification and data capture techniques - Bar code symbol print quality test specification - Two-dimensional symbols. The main technical deviations with respect to ISO/IEC 15415:2011 and the reasons are as follows: ——The adjustments of technical deviations are made for the normative references in this standard so as to adapt to the technical conditions of China. The adjustments are mainly reflected in Clause 2 "Normative references", with the specific adjustments as follows:  ISO/IEC 15416 is replaced by GB/T 14258 which is modified in relation to the international standard;  ISO 7724-2:1984 is replaced by GB/T 11186.2 which is modified in relation to the international standard;  ISO/IEC 19762-1 and ISO/IEC 19762-2 are replaced by the newly revised ISO/IEC 19762;  GB/T 2828.1, GB/T 6378.1, GB/T 12905, GB/T 18284, GB/T 21049, GB/T 35402, ISO/IEC 16022, ISO/IEC 16023 and ISO/IEC 24778 are added (see Clause 2). ——The measurement process of two-dimensional matrix bar code is described by means of items (see 7.1); ——The representation of the parameter range corresponding to each grade in the grading tables is modified, for example: the parameter range corresponding to grade 3 in Table 2 is changed to 0.64≤CY<0.71, and it is inaccurately represented by ≥64% in Table 2 of ISO/IEC 15415:2011 (see Table 2, Table 3, Figure 2, Table 5, Table 6, Table 8, Table 9, Table 10, Table 11). ——The required "the interim codeword grade of each parameter (Modulation, Defects and Decodability) for each codeword is the highest codeword grade for that parameter obtained on any scan for that codeword" is modified to "the interim codeword grade of each parameter for each codeword is the highest codeword grade for that parameter obtained on any scan for that codeword" (see 6.2.5); ——The concepts of "module MOD", "codeword MOD", "symbol MOD", "module RM", "codeword RM" and "symbol RM" are added (see 7.8.4).   For the purposes of this standard, the following editorial changes and structural adjustments have also been made: ——The order of annexes in ISO/IEC 15415:2011 is adjusted herein so that Annex A hereof corresponds to Annex D of ISO/IEC 15415:2011, Annex B hereof corresponds to Annex F of ISO/IEC 15415:2011, Annex C hereof corresponds to Annex B of ISO/IEC 15415:2011, Annex D hereof corresponds to Annex A of ISO/IEC 15415:2011, Annex E hereof corresponds to Annex C of ISO/IEC 15415:2011, and Annex F hereof corresponds to Annex E of ISO/IEC 15415:2011. ——Annex G (Informative) "Examples of two-dimensional bar code symbol test report" is added. This standard was proposed by and is under the jurisdiction of SAC/TC267 National Technical Committee on Logistics Information Management of Standardization Administration of China.   Introduction The technology of bar coding is based on the recognition of patterns encoded, in bars and spaces or in a matrix of modules of defined dimensions, according to rules defining the translation of characters into such patterns, known as the symbology specification. Bar codes may be categorised into linear bar codes, on the one hand, and two-dimensional bar codes on the other; the latter may in turn be sub-divided into "two-dimensional multi-row bar codes", sometimes referred to as "two-dimensional stacked bar codes", and "two-dimensional matrix bar codes". In addition, there is a hybrid group of symbologies known as "composite symbologies"; these symbols consist of two components carrying a single message or related data, one of which is usually a linear symbol and the other a two-dimensional symbol positioned in a defined relationship with the linear symbol. Two-dimensional multi-row bar code symbols are constructed graphically as a series of rows of symbol characters, representing data and overhead components, placed in a defined vertical arrangement to form a (normally) rectangular symbol, which contains a single data message. Each symbol character has the characteristics of a linear bar code symbol character and each row has those of a linear bar code symbol; each row, therefore, may be read by linear symbol scanning techniques, but the data from all the rows in the symbol must be read before the message can be transferred to the application software. Two-dimensional matrix bar code symbols are normally rectangular arrangements of dark and light modules, the centres of which are placed at the intersections of a grid; the coordinates of each module need to be known in order to determine its significance, and the symbol must therefore be analysed two-dimensionally before it can be decoded. Dot codes are a subset of two-dimensional matrix bar codes in which the individual modules do not directly touch their neighbours but are separated from them by a clear space. Unless the context requires otherwise, the term “symbol” in this standard may refer to either type of two-dimensional bar code symbology. The bar code symbol must be produced in such a way as to be reliably decoded at the point of use, if it is to fulfill its basic objective as a machine-readable data carrier. Manufacturers of bar code equipment and the producers and users of bar code symbols therefore require publicly available standard test specifications for the objective assessment of the quality of bar code symbols, to which they can refer when developing equipment and application standards or determining the quality of the symbols. This standard forms the basis of the process control and quality assessment during bar code equipment manufacturing, bar code symbol production and use. The performance of measuring equipment for the verification of bar code symbols may be in accordance with GB/T 26228.1 and ISO/IEC 15426-2. This standard is intended to achieve comparable quality assessment results to the linear bar code symbol print quality standard GB/T 14258, the general principles of which it has followed. It shall be read in conjunction with the symbology specification applicable to the bar code symbol being tested, which provides symbology-specific detail necessary for its application. Two-dimensional multi-row bar code symbols are verified according to the GB/T 14258 methodology, with the modifications described in Clause 6; different parameters and methodologies are applicable to two-dimensional matrix bar code symbols. There are currently many methods of assessing bar code quality at different stages of symbol production. The methodologies described in this standard are not intended as a replacement for any current process control methods. They provide symbol producers and their trading partners with universally standardized means for communicating about the quality of two-dimensional bar code symbols after they have been printed. The procedures described in this standard shall necessarily be augmented by the reference decode algorithm and other measurement details within the applicable symbology specification, and they may also be altered or overridden as appropriate by governing symbology or application specifications. Alternative methods of quality assessment may be agreed between parties or as part of an application specification. Two-dimensional bar code symbol print quality test 1 Scope This standard specifies methods for testing, grading and overall quality assessment of two-dimensional multi-row and matrix bar code symbols, and gives information on possible causes of deviation from optimum grades and appropriate corrective action. This standard is applicable to the print quality test of those two-dimensional bar code symbols for which a reference decode algorithm has been defined in the two-dimensional bar code symbology specifications, but its methodologies can be applied partially or wholly to the test of two-dimensional bar code symbols of other similar symbologies. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated reference, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. GB/T 2828.1 Sampling procedures for inspection by attributes - Part 1: Sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection (GB/T 2828.1-2012, ISO 2859-1:1999, IDT) GB/T 6378.1 Sampling procedures for inspection by variables - Part 1: Specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection for a single quality characteristic and a single AQL (GB/T 6378.1-2008, ISO 3951-1:2005, IDT) GB/T 11186.2 Methods for measuring the colour of paint films - Part 2: Colour measurement (GB/T 11186.2-1989, idt ISO 7724-2:1984) GB/T 12905 Bar code terminology GB/T 14258 Information technology - Automatic identification and data capture techniques--Verification of print quality of bar code symbols (GB/T 14258-2003, ISO/IEC 15416:2000, MOD) GB/T 18284 QR Code (GB/T 18284-2000, neq ISO/IEC 18004:2000) GB/T 21049 Chinese-sensible code GB/T 35402 Direct part mark (DPM) two dimensional bar code symbol quality test (GB/T 35402-2017, ISO/IEC TR 29158:2011, MOD) ISO/IEC 16022 Information technology - Automatic identification and data capture techniques - Data Matrix bar code symbology specification ISO/IEC 16023 Information technology - Automatic identification and data capture techniques - Bar code symbology specification - MaxiCode ISO/IEC 19762 Information technology - Automatic identification and data capture (AIDC) techniques - Harmonized vocabulary ISO/IEC 24778 Information technology - Automatic identification and data capture techniques - Aztec Code bar code symbology specification 3 Terms and definitions For the purposes of this document, the terms and definitions given in GB/T 12905, GB/T 14258 and ISO/IEC 19762 and the following apply. 3.1 pixel individual light-sensitive element in an array of image capture device [e.g. CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) device] 3.2 effective resolution resolution obtained by the measuring device on the surface of the symbol under test, normally expressed in pixels per millimetre or pixels per inch, and calculated as the resolution of the image capture element multiplied by the magnification of the optical system of the measuring device 3.3 error correction capacity number of codewords in a two-dimensional bar code symbol (or error correction block) assigned for erasure and error correction, minus the number of codewords reserved for error detection 3.4 inspection area rectangular area which contains the entire symbol to be tested inclusive of its quiet zones 3.5 grade threshold boundary value separating two grade levels, the value itself being taken as the lower limit of the upper grade 3.6 module error module of which the apparent dark or light state in the binarised image is inverted from its intended state   3.7 raw image plot of the reflectance values in X and Y coordinates, representing the actual reflectance values from each pixel of the light-sensitive array 3.8 reference grey-scale image plot in X and Y coordinates, obtained by convolving the raw image with a synthesised circular aperture 3.9 binarised image binary (black/white) image created by applying the Global Threshold to the reference grey-scale image 3.10 sample area area of an image contained within a circle 0.8X in diameter, X being the average module width determined by the application of the reference decode algorithm for the symbology in question or, where the application permits a range of X dimensions, the minimum module width permitted by the application specification 3.11 scan grade result of the assessment of a single scan of a two-dimensional matrix bar code symbol, derived by taking the lowest grade achieved for any measured parameter of the reference grey-scale and binarised images 3.12 reflectance margin measurement of modulation using error correction and known module colours 4 Symbols and abbreviated terms For the purpose of this document, the following symbols and abbreviated terms apply. AN: Axial Nonuniformity DPM: Direct Part Marking Ecap: error correction capacity. e: number of erasures. FPD: Fixed Pattern Damage GN: Grid Nonuniformity GT: Global Threshold MOD: modulation. MARGIN: reflectance margin of a module. RM: Reflectance Margin Rmax: the highest reflectance in any element or quiet zone in a scan reflectance profile, or the highest reflectance of any sample area in a two-dimensional matrix bar code symbol. Rmin: the lowest reflectance in any element in a scan reflectance profile, or the lowest reflectance of any sample area in a two-dimensional matrix bar code symbol. SC: Symbol Contrast. (SC=Rmax-Rmin) t: number of errors. UEC: Unused Error Correction 5 Quality grading 5.1 General The measurement of two-dimensional bar code symbols is designed to yield a quality grade which can be used for symbol quality judgment and process control purposes, and which is broadly predictive of the read performance to be expected of the symbol in various environments. As a consequence of the use of different types of reading equipment under differing conditions in actual applications, the levels of quality required of two-dimensional bar code symbols to ensure an acceptable level of performance will differ. The required symbol grade shall be determined in the symbol grade form specified in this standard by referring to Annex A, A.4. Samples shall be taken from the tested sample batch according to the statistically valid number of samples, and the minimum acceptable symbol grade shall be determined. If no sampling plan is specified in the quality control process or the agreement between both parties, an appropriate sampling plan may be selected according to GB/T 2828.1 or GB/T 6378.1. 5.2 Expression of quality grades Each parameter may have an alphabetic or numeric grade. The numeric grades express different quality grades on a descending scale from 4 to 0. The grade 4 represents the highest quality, while the grade 0 represents failure. The alphabetic grades are expressed on an alphabetic scale from A to F, with a failing grade of F. Table 1 maps the alphabetic and numeric grades to each other. Table 1 Equivalence of numeric and alphabetic quality grades Numeric grade Alphabetic grade 4 A 3 B 2 C 1 D 0 F 5.3 Overall symbol grade values The overall symbol grade shall be calculated as defined in 6.2.6 or 7.10. Overall symbol grades shall be expressed to one decimal place on a numeric scale ranging in descending order of quality from 4.0 to 0.0. Where a specification defines overall symbol grades in alphabetic terms, the relative mapping of the alphabetic and numeric grades is as illustrated in Figure 1 below. For example, the range of 1.5 to immediately below 2.5 corresponds to grade C. Figure 1 Mapping of alphabetic and numeric overall symbol grades 5.4 Reporting of symbol grade A symbol grade is only meaningful if it is reported in conjunction with the illumination and aperture used. It shall be shown in the format: grade/aperture/measuring light wavelength/angle, where: ——"grade" is the overall symbol grade as defined in 5.3. ——"aperture" is the aperture reference number (from GB/T 14258 for linear scanning techniques, or from 7.3.3 for two-dimensional matrix bar codes). ——"measuring light wavelength" is a numeric value indicates the peak light wavelength in nanometres (for narrow band illumination); the alphabetic character W indicates that the symbol has been measured with broadband illumination ("white light") the spectral response characteristics of which must imperatively be defined or have their source specification clearly referenced. ——"angle" defines the angle of incidence of the illumination. Its absence indicates that the angle of incidence is 45°. It shall be included in the reporting of the overall symbol grade when the angle of incidence is other than 45°. Note: While illumination from four sides with an angle of incidence of 45° is the default, other angles of incidence, i.e., 30°and 90°, may be specified. In DPM test, the angle of illumination needs to use a combination of numeric and alphabetic angle indicators, see GB/T 35402. An asterisk following the value for "grade", in the case of a two-dimensional matrix bar code symbol, indicates that the surroundings of the symbol contain extremes of reflectance that may interfere with reading, see 7.7. Example 1: 3.0/05/660 would indicate that the average of the grades was 3.0 when it is obtained with the use of a 0.125mm aperture (ref. no. 05) and a 660nm light source, incident at 45°. Example 2: 3.0/10/W/30 would indicate the grade of a symbol intended to be read in broadband light, measured with light incident at 30° and using a 0.250mm aperture (ref. no. 10), but would need to be accompanied either by a reference to the application specification defining the reference spectral characteristics used for measurement or a definition of the spectral characteristics themselves. Example 3: 3.0*/10/670 would indicate the grade of a symbol measured using a 0.250mm aperture (ref. no. 10), and a 670nm light source, and indicates the presence of a potentially interfering extreme reflectance value in the surroundings of the symbol.   6 Measurement methodology for two-dimensional multi-row bar code symbols 6.1 General The evaluation of two-dimensional multi-row bar code symbols shall be based on the application of the methodology of GB/T 14258, as described in 6.2.2 or 6.3, and if appropriate for the symbology, on the application of the additional provisions described in 6.2.3, 6.2.4 and 6.2.5, to derive an overall symbol grade. Ambient light levels shall be controlled in order not to have any influence on the measurement results. The symbol shall be scanned using the light wavelength(s) and effective aperture size specified in the appropriate application standard. When performing a measurement, the scan lines shall be made perpendicular to the height of the bars in the start and stop characters and shall as far as possible pass through the centres of rows in order to minimise the effect of cross-talk from adjacent rows. In the case of area imaging techniques, a number of scan lines, perpendicular to the height of the bars and sufficient to cover all rows of the symbol, shall be synthesised by convolving the raw image with the appropriate synthetic aperture. 6.2 Symbologies with cross-row scanning ability 6.2.1 Basis of grading The distinguishing feature of these symbologies is their ability to be read with scan lines that cross row boundaries. Symbologies of this type also share the feature that the start and stop patterns (or equivalent features of the symbol, e.g. the Row Address Patterns of MicroPDF417) are constant from row to row, or the position of only one edge in these patterns varies by no more than 1X in adjacent rows of the symbol. These symbologies shall be graded in respect of: ——Analysis of the scan reflectance profile (see GB/T 14258 and 6.2.2); ——Codeword Yield (see 6.2.3); ——Unused Error Correction (see 6.2.4); ——Codeword print quality (see 6.2.5). 6.2.2 Grade based on analysis of scan reflectance profile The start and stop or equivalent (e.g. Row Address) patterns of the symbol shall be evaluated according to GB/T 14258. Regions with data content will be evaluated separately as described in 6.2.3, 6.2.4 and 6.2.5. Test scans of the start and stop patterns shall be graded using all parameters specified in GB/T 14258. The effective aperture size is specified in the appropriate application standard or is the default aperture size appropriate for the symbol X dimension given in GB/T 14258. For the analysis of the scan reflectance profiles, the number of scans shall be 10, or the quotient (integer part) obtained by dividing the height of the symbol by the measuring aperture, whichever is smaller. Scans shall be approximately evenly spaced over the height of the symbol. For example, in a twenty-row symbol the ten scans shall be performed in alternate rows. In a two-row symbol, up to five scans might be performed in each row, at different positions in the height of the bars. The symbology specification may give more specific guidance on the selection of the scans to be used. To identify bars and spaces, a Global Threshold for each scan has to be determined. Global Threshold shall be equal in reflectance to 1/2 of the sum of the highest and the lowest reflectances in the scan. All regions above the Global Threshold shall be considered spaces (or quiet zones) and all regions below shall be considered bars. Edge locations shall be determined as the points where the reflectance value is midway between the highest reflectance in the adjoining space (including quiet zones) and the lowest reflectance in the adjoining bar in the scan reflectance profile. For the evaluation of the parameters "reference decode" and "decodability", the reference decode algorithm for the symbology shall be applied. Each scan shall be graded as the lowest grade for any individual parameter in that scan. The grade based on scan reflectance profiles shall be the arithmetic mean of the grades for the individual scans. The measurement of bar width average gain or loss may be used for process control purposes. Note that this method will not be sensitive to printing variations parallel to the height of the start and stop characters. If a full analysis of the printing process is desired, symbols should be printed and tested in both orientations. 6.2.3 Grade based on Codeword Yield The Codeword Yield (CY) measures the efficiency with which linear scans can recover data from a two-dimensional multi-row symbol. The Codeword Yield is the number of validly decoded codewords expressed as a percentage of the maximum number of codewords that could have been decoded (after adjusting for tilt). A poor Codeword Yield, for a symbol whose other measurements are good, may indicate a Y-axis print quality problem (such as those shown in Annex E, Table E.1). Obtain a matrix of the correct symbol character values, such as would result from successful completion of the UEC calculations (see 6.2.4). This matrix is used as the "final decode of the symbol" used in subsequent steps to determine validly decoded codewords.   An individual scan qualifies for inclusion in the Codeword Yield calculation if it meets either of two conditions: ——The scan did not include recognised portions of either the top or the bottom row of the symbol. At least one of the Start or Stop (or Row Address) patterns shall have been successfully decoded from that scan, together with at least one additional codeword or the corresponding second Start or Stop pattern, or Row Address Pattern. ——The scan included recognised portions of either the top or the bottom row of the symbol. Both the Start and Stop patterns of the symbol shall have been successfully decoded from that scan. It is important to note that an extension to the symbology’s Reference Decode Algorithm is required, in order to detect and decode a pair of Start and Stop patterns when neither of the adjacent codewords is decodable. As examples, a linear search for a matching pair of PDF417 Start and Stop patterns, or a linear search for a matching pair of MicroPDF417 Row Indicator Patterns, would fulfill this requirement for scans where the Reference Decode Algorithm alone did not decode both patterns; thus this extension can qualify a scan where no codewords (other than the matched end patterns) were decoded. Note however, that a scan that contains only a single decoded Start or Stop pattern found by this linear search does not count as a qualified scan, if no other codewords or corresponding second Start or Stop pattern, or Codeword or Row Address Pattern, were also decoded. Decode the symbol completely and populate the symbol matrix. For each qualified scan, compare the codewords actually decoded with the codewords in the symbol matrix and count the number of codewords that match. Accumulate the total number of validly decoded codewords, and update a count of the number of times each codeword of the symbol has been decoded and a count of the number of times each row has been detected. Also record a count of the number of detected row crossings in each scan (a crossing is “detected” when a scan line yields correctly-decoded codewords from adjacent rows). After processing each scan, calculate the maximum number of codewords that could have been decoded thus far, as the number of qualified scans multiplied by the number of columns in the symbol (excluding the fixed patterns, such as the Start and Stop patterns of PDF417 or the Row Address Indicators of MicroPDF417). The entire symbol shall be scanned multiple times until three conditions are met: a) the maximum number of codewords that could have been decoded is at least ten times the number of codewords in the symbol; b) the highest and lowest decodable rows (which may not necessarily be the first and last rows) of the symbol have each been scanned at least three times; and c) at least (0.9n) of the codewords (data or error correction) have been successfully decoded two or more times, where n is the number of non-error-correction data codewords in the symbol. Example: Taking a PDF417 symbol with 6 rows and 16 columns and error correction level 4, the total number of codewords is 96, of which 64 are data and 32 error correction. To fulfill condition 1, the maximum number of codewords that could have been decoded must be at least 960. To fulfill condition 3, since n is 64, at least 58 of the codewords must have been decoded twice or more (0.9×64=57.6). If the ratio of the total number of validly decoded codewords to the total number of detected row crossings is less than 10:1, then discard the measurements just obtained, and repeat the measurement process, adjusting the tilt angle of the scan line to reduce the number of row crossings. Otherwise, to compensate for any residual tilt, subtract the number of detected row crossings from the calculated maximum number of codewords that could have been decoded. Codeword Yield shall be graded as shown in Table 2. Table 2 Grading of Codeword Yield Codeword Yield (CY) Grade CY≥0.71 4 0.64≤CY<0.71 3 0.57≤CY<0.64 2 0.50≤CY<0.57 1 CY<0.50 0 6.2.4 Grade based on unused error correction Decode the symbol completely and process scans until the number of decoded codewords stabilises. Calculate the unused error correction (UEC) using the following formula. UEC=1-(e+2t)/Ecap where, e——the number of erasures; t——the number of errors; Ecap——the error correction capacity of the symbol. If no error correction has been applied to the symbol, and if the symbol decodes, UEC=1. If (e+2t) is greater than Ecap, UEC=0. In symbols with more than one error correction block, UEC shall be calculated for each block independently and the lowest value shall be used for grading purposes. Unused Error Correction shall be graded as shown in Table 3. Table 3 Grading of Unused Error Correction Unused Error Correction (UEC) Grade UEC≥0.62 4 0.50≤UEC<0.62 3 0.37≤UEC<0.50 2 0.25≤UEC<0.37 1 UEC<0.25 0 6.2.5 Grade based on codeword print quality This subclause gives an approach for the assessment of the Decodability, Defects and Modulation parameters. This approach is based on the parameter grading of scan reflectance profile in GB/T 14258, and at the same time takes into account the effect of error correction in symbol quality parameters such as Decodability, Defects and Modulation by error correction. See Annex B for the correction method. This approach uses the following procedure for the assessment of each of the three parameters. In symbols with more than one error correction block, it shall be applied to each block independently and the lowest value shall be used for grading purposes. The entire symbol shall be scanned until 0.9n codewords (where n has the same meaning as in 6.2.3) have been decoded more than ten times or until it is certain that each codeword has been scanned at least once without inter-row interference. In each scan, the Decodability, Defects and Modulation parameters shall be measured in each symbol character in accordance with GB/T 14258. The calculation of all three parameters shall be based on the value of Symbol Contrast obtained from Rmax and Rmin in that scan reflectance profile. The interim codeword grade of each parameter for each codeword is the highest codeword grade for that parameter obtained on any scan for that codeword.

Foreword II Introduction V 1 Scope 2 Normative references 3 Terms and definitions 4 Symbols and abbreviated terms 5 Quality grading 5.1 General 5.2 Expression of quality grades 5.3 Overall symbol grade values 5.4 Reporting of symbol grade 6 Measurement methodology for two-dimensional multi-row bar code symbols 6.1 General 6.2 Symbologies with cross-row scanning ability 6.3 Symbologies requiring row-by-row scanning 7 Measurement methodology for two-dimensional matrix bar code 7.1 General 7.2 Obtaining the test images 7.3 Reference reflectivity measurements 7.4 Requirements of scans 7.5 Scan grading 7.6 Grading procedure 7.7 Additional reflectance check over extended area 7.8 Image assessment parameters and grading 7.9 Scan grading 7.10 Overall symbol grade 7.11 Print growth 8 Measurement methodologies for composite symbologies 9 Substrate characteristics Annex A (Informative) Guidance on selection of grading parameters in application specifications Annex B (Informative) Parameter grade overlay applied to two-dimensional bar code symbols Annex C (Informative) Quality grading flowchart for two-dimensional matrix bar code symbols Annex D (Normative) Symbology-specific parameters and values for symbol grading Annex E (Informative) Interpreting the scan and symbol grades Annex F (Informative) Substrate characteristics Annex G (Informative) Examples of two-dimensional bar code symbol test report Bibliography