1、International Standard 1831 0 4iY% 4 INTERNATIONAL ORGANIZATION FOR STANDARDIZATION*ME)YHAPOHAR OPrAHH3AUMR n0 CTAHAAPTkl3Al 0.009 in diameter) covering the nearest void or group of voids likewise having a total surface greater than one-third of that of its circle, shall be at least 1 mm (0.04 in).
2、Non-allowable void 7 Maximum COL 7 lmm lLMinimum COL Figure 9 - Voids 11 Copyright American National Standards Institute Provided by IHS under license with ANSINot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 1831-1980 (E) 5.4.4.5 Edge irregularity (see figure 1
3、0) An edge irregularity exists where the character extends outside the maximum COL and/or where a part of the character is miss- ing inside the minimum COL. An edge irregularity shall be allowed if the projecting part of the character measured along the maximum COL and/or the missing part of the cha
4、racter measured along the minimum COL does not exceed 0,3 mm (0.012 in). Furthermore, the distance between adjacent ir- regularities shall be at least 1 mm (0.04 in) measured centre to centre. 5.4.4.8 Spots (see figure 11) Spots are areas outside the maximum COL which contrast with the background. T
5、he distinction between allowable spots and non-allowable spots is based on a measurement of their size and distance. Spots may be connected or adjacent to parts of the printed image, or may be free standing within the clear area (see 6.10). When the measuring gauge is in best fit to a charac- ter, a
6、ny extraneous ink outside the maximum COL is a spot. Any extraneous ink of sufficient area, that is nearly as dark or darker than the lightest printing within the minimum COL, shall be checked. One or more spots shall be allowable if contained entirely in an inspection circle of 0,2 mm (0.008 in) di
7、ameter and if their total surface is smaller than one-third of the surface of the circle. If their total surface is greater than one-third of that of the ins- pection circle but is contained entirely within the inspection circle, then the distance between the centre of this circle and the centre of
8、the inspection circle (0,2 mm; 0.008 in diameter) covering the nearest spot or group of spots likewise having a total surface greater than one-third of that of its circle, shall be at least 1 mm (0.04 in). Dimensions in millimetres Allowable edge irregularity Maximum COL Mizum COL Minimum COL Maximu
9、m COL L Non-allowable edge irregularity Figpre 10 - Edge irregularity 12 Copyright American National Standards Institute Provided by IHS under license with ANSINot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 1831-1980 (E) owed in unlimited number Allowable spot
10、s Non-allowable spots 0.2 mm circle Maximum COL Minimum COL Figure 11 - Spots 5.4.5 Instrumented measurement 5.4.5.1 Apparatus arrangement Illumination : Incandescent lamp. Geometry of illumination : One source at 45” with respect to paper surface. Illuminated area large compared with measuring aper
11、ture. Geometry of scanner : 90 with respect to paper surface. Aperture 0,2 mm (0.009 in) diameter at sample surface. Spectral response : See 3.2. White reference : See 4.2. 5.4.5.2 Print contrast (see figure 12) Print contrast is the difference between the reflectance R, of a character and the refle
12、ctance R,., of the paper on which it is printed. PC = R, - R, where RW is the maximum reflectance found within the area of interest to which the PC of point p is referenced. (In measuring printed images, the area of interest shall be a rec- tangle of approximately twice the nominal character height
13、by twice the nominal character width and centred on the character being measured.) R, is the reflectance from a small measurement area centred on point p. The reflectances R, and R, shall be measured within an area of 0,2 mm (0.009 in) diameter, if circular, or 0,15 mm (0.005 9 in) side, if square.
14、These reflectance specifications deal only with diffuse reflec- tance, and the reflected light used for measurement shall ex- clude specularly reflected light. Reflectance measurements of R, and R, shall be referred to BaS04 as the 100 % value when determining the value of PC. The reflectance measur
15、ements shall be made using the black backing method. The PC of any point of a printed image is highly dependent on the spectral properties of the ink used to create the printed image. 5.4.5.3 Print contrast signal The print contrast signal (PCS) is defined by : PCS = Rw - R, RW It relates the print
16、contrast of any selected point to the reflec- tance of the paper on which it is printed. Although normally reflectance values are referred to BaS04 as the 100 % value, this is not necessary in the determination of PCS. The value of PCS is dependent only on the relative reflectance values of R, and R
17、,. 13 Copyright American National Standards Institute Provided by IHS under license with ANSINot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 1831-1980 (E) -_- I Base Dimensions in millimetres - -4 1 H 2w k Figure 12 - Print contrast 14 Copyright American Nation
18、al Standards Institute Provided by IHS under license with ANSINot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 1831-1980 (E) 5.4.5.4 Best fit All measurements described hereafter shall be made in the “best fit” position of the character with the COL masks. The b
19、est fit can be achieved visually on an instrument by pos- itioning the actual character image so that it fills the minimum COL as much as possible and at the same time does not extend beyond maximum COL. More specifically, the overall reflec- tance within minimum COL shall be a minimum. If this con-
20、 dition is met for several positions, then the best fit position is that yielding the maximum reflectance outside maximum COL. Light portions of the character inside minimum COL, and dark portions outside maximum COL, shall be checked as to edge irregularities, voids and spots. Maximum COL Minimum C
21、OL 5.4.5.6 PCS, pc%lax is the highest average PCS value of three consecutive basic PCS values for characters with a centreline longer than 2 mm (0.08 in) and of five such consecutive values for characters with a centreline of less than 2 mm (0.08 in). 5.4.5.7 PCS,in PCS,rn is the lowest average PCS
22、value of three consecutive basic PCS values for characters with a centreline longer than 2 mm (0.08 in) and of five such consecutive values for characters with a centreline of less than 2 mm (0.08 in). 5.4.5.8 Contrast variation ratio within a character The variation of contrast within a character i
23、s defined by the contrast variation ratio : pwnax CVR =- pcsrnin The CVR must satisfy the following conditions : CVR 0,80 in range X PCS.80 % 050 in range Y For certain OCR applications, the value given for PCS80 % in range Y might be too stringent. Deviations from this value shall be agreed upon by
24、 the parties concerned. Voids are areas inside the minimum COL which have a significantly lower density than the printed image. The distinc- tion between allowable voids and non-allowable voids is based on a measurement of their size and distance. Small voids shall be permitted providing certain con
25、ditions are satisfied; larger ones shall not. The size of a void depends on the PCS level at which it is measured. A void shall be allowable if it satisfies the following conditions : All basic PCS values lower than PCSac % shall be considered. The values d mentioned hereafter are : d = 040 in range
26、 X d = 0,35 in range Y A void is present at points for which a PCS of less than d is measured. a) Characters with a centreline of more than 2 mm (0.08 in) : - if a point has a PCS d, an allowable void is present at this point; - if two adjacent points have a PCS e, the spot shall not be allowable; -
27、 if at most one position has a PCS e, the spot shall be allowable; - if two positions have a PCS e, the aperture shall be centred on the position with the smaller PCS and the seven remaining positions defined by steps of 0,l mm (0.004 in) horizontally and vertically are also measured : - if a third
28、position is found with a PCS e, the spot shall not be allowable: - if no third position with a PCS e is found, the spot shall be allowable only if its distance to a spot of the same type and to the maximum COL is greater than 1 mm (0.04 in). If in this procedure one or more positions happen to have
29、their centre within maximum COL, these positions shall be disregarded. Spots remote from the character, i.e. outside the area of in- terest, are not subject to PCS limitations. However, if located in the clear area (see 6.10) their size shall be limited to 0,2 mm (0.008 in) in diameter. 5.4.6 Comput
30、er-aided method An implementation of this method exists and is described in annex C. 5.4.6.1 Apparatus arrangement The characteristics of the high resolution scanner to be used shall be in accordance with the following arrangement : Spatial resolution : 25 pm (0.001 in) or of higher degree. 5.4.5.12
31、 Spots Aperture : Spots are areas outside the maximum COL which contrast with the background. The distinction between allowable spots and non-allowable spots shall be based on a measurement of their size. Small spots shall be permitted providing certain conditions are satisfied; larger ones shall no
32、t. Spots may be connected or adjacent to parts of the printed image, or may be free standing. Spots shall be measured with an aperture of 0,2 mm (0.008 in) diameter, centred on the spot at the point with the highest PCS value. When this position is identified, the eight positions defined by the step
33、s of 0,l mm (0.004 in) horizontally and ver- tically shall also be measured. 25 pm (0.001 in) in diameter or equivalent to the degree of resolution. Geometry of illumination : One source at 45O with respect to the paper surface with a large illuminated area compared with the measuring aper- ture. Al
34、ternatively, an illumination with a small aperture size at 9o” with respect to the paper. 16 Copyright American National Standards Institute Provided by IHS under license with ANSINot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 1831-1980 (E) Geometry of scanner
35、 : 90” with respect to the paper surface. Aperture 0,2 mm (0.008 in) diameter at sample surface. Alternatively, one scanner with large sensitive area at 45O with respect to the paper. Spectral response : See 3.2. White reference : See 4.2. All definitions of print parameters given hereafter are base
36、d upon an integration of the scanned values up to a circular area of 0.2 mm (0.008 in) diameter. 5.4.6.2 Print contrast (see table 6) The print contrast is the difference between the reflectance (R,) of the area of the paper on which the character is printed and the reflectance (R,) of the point und
37、er inspection. R, is the maximum reflectance of the paper. R, shall be measured in a rectangle Q which is centred upon the character to be investigated. The dimensions for the rectangle Q are shown in table 6. Grey scale resolution : R, is the reflectance at the point p under consideration. 32 or mo
38、re grey levels. The results from a measuring arrangement with a large area of illumination and a small scanner area are comparable with those received by an arrangement containing a small area of illumina- tion and a large scanner area. An arrangement with a small area of illumination and a small si
39、zed scanner shall not be permitted. If the spectral response of the optical character recognition system in use is known, the parameters of the printed images may be tested in this spectral band only. Otherwise testing shall be performed in all spectral bands that are mentioned in 2.2. While measuri
40、ng these parameters, the paper shall be backed by a medium with less than 3 % reflectance. 5.4.6.3 Definition of the print contrast signal The PCS is defined by the equation PCS = Rw - 4, RW Table 6 - Print contrast Font A Size I III IV Character set All characters as defined in IS0 1073 Height X wi
41、dth of rectangle Cl mm in 3.90 X 2.50 0.164 x 0.100 4.80 X 2.70 0.190 x 0.107 5,60 X 3,40 0.221 x 0.134 B I III IV Sub-sets 1, 2 4.90 X 2.50 0.170 x 0.100 Sub-sets 3, 4 3,30 X 2.50 0.154 x 0.100 All characters as defined in 4.80 X 2,70 0.190 x 0.107 IS0 1073 5.40 x 3.50 0.213 X 0.138 17 Copyright Am
42、erican National Standards Institute Provided by IHS under license with ANSINot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 1831-1980 (E) 5.4.6.4 Best fit 5.4.6.8 Contrast variation within a character 5.4.6.4.1 General All measurements and investigations on para
43、meters that are specified in the following shall be performed after centring the COL gauge upon the printed character (best fit). Definition of best fit : The COL gauge shall be adjusted to be either perpendicular or parallel to the document reference edge. For determination of the printed character
44、, the preliminary stroke edges of the character shall be defined. For this reason the arithmetical average PCS, of all PCSs equal to or greater than 0,3 within the rectangle Q shall be established. The preliminary stroke edges are then found at PCS2 = 0,5.(PCS, + 0,3). The COL gauge shall be moved h
45、orizontally and vertically along the so defined preliminary stroke edges of the character until the position is found where the deviation from the minimum COL and maximum COL is at a minimum. If there are several such positions, the position with the highest value for PCSso 9/a shall be chosen (see
46、5.4.6.5). 5.4.6.4.2 Characters with cut-off All characters for all print tolerance ranges shall be centred in this way without considering the cut-off limit lines see figure 7 a). For those characters of print tolerance range Z which do not satisfy the conditions of the following specifica- tions, t
47、he best fit positioning shall be repeated. This second step for best fit shall be performed by using the cut-off limit lines see figure 7 b). Thereafter all parameters shall be tested under consideration of the cut-off limit lines. 5.4.6.5 PCS within a character The smallest value of the 80 % highes
48、t values measured along the centreline is called PCSac %. It shall satisfy the following conditions : PCSm 9/o 0,60 in range X PCS80 9/o 050 in range Y PCS the higher the grammage, the greater the opacity. Consequently, there is a similar relationship between opacity and paper thickness, although th
49、e use of filler and coating materials have an effect. In general, paper having an opacity exceeding 85 % should be used. Papers of lower opacity should be used only if needed for the ap- plication and after considering the scanner optical system. Papers having an opacity less than 70 % should not be used. Many inks have the property of permeating the paper to a considerable depth, Applications requiring an OCR document to be printed on both sides
