ANSI INCITS ISO IEC 9541-3-1994 Information technology - Font information interchange - Part 3 Glyph shape representation (Adopted by INCITS).pdf

1、INTERNATIONAL STANDARD ISO/IEC 9541-3 First edition 1994-05-01 Information technology - Font information interchange - Part 3: Glyph shape representation Technologies de /information - cchange dinformations sur /es fontes - Partie 3: Repr - hold at least 24 objects in the operand list. 1.3 Normative

2、 references The following standards contain provisions which, through reference in this text, constitute provisions of this part of ISO/IEC 9541. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO/

3、IEC 9541 are encouraged to investigate the possibility of ap- plying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. ISO/IEC 9541-3:1994(E) Q ISO/IEC ISO/lEC 8824: 1990, Information technology - Open Sys

4、tems Interconnection - Specification of Abstract Syntax Notation One (ASN. 7). ISO/IEC 8825:1990, information technology - Open Systems Interconnection - Specification of Basic Encoding Rules for Abstract Syntax Notation One IASN. 1). IS0 8879: 1986, Information processing - Text and office systems

5、- Standard Generalized Markup Language (SGML). ISO/IEC 9070:1991, information technology - SGML support facilities - Registration procedures for public text owner identifiers. ISO/IEC 9541-1 :1991, Information technology - Font information interchange - Part I: Architecture. ISO/IEC 9541-2:1991, Inf

6、ormation technology - Font information interchange - Part 2: Interchange Format. ISO/I EC 10036:1993, Information technology - Font information interchange - Procedure for registration of glyph and glyph collection identifiers. 1.4 Notation The formal structure of glyph shape properties is specified

7、 using the BNF notation described in clause 4 of ISO/IEC 9541. 1.5 Overview of glyph shape representation Each glyph shape representation technique makes use of different properties in specifying glyph shapes and therefore has its own architecture and interchange format. In this par-t of ISO/IEC 954

8、1 each glyph shape repre- sentation technique is defined in a separate section. The glyph shape representation currently defined is - IS0 Standard Type 1 Glyph Shape Representation (specified in section 2) NOTE 1 This part of ISOAEC 9541 may be extended in the future by the addition of further secti

9、ons specifying additional glyph shape representation techniques. Glyph shape representations are divided into two broad categories: outline and bitmap representations of glyph shapes. An outline representation describes a glyph using a mathematical description of the edges of glyph shapes. This has

10、the advantage of allowing transformations such as scaling, rotation, and skewing, and permits many variations of style without additional storage requirements. An outline format also facilitates incorporation of added scaling information, called hints, which aid in the preservation of proportions fo

11、r all sizes of raster grids (however, their usefulness is not confined to raster devices). Hints can also aid in achieving nonlinear scaling as an optical cor- rection for different absolute sizes of presented glyphs. For raster devices, outline fonts are converted, after adjustments for scaling req

12、uirements, to bitmap represent- ations for final imaging and presentation. However, the presentation of outline glyph shape descriptions is not limited to raster devices; it may also include vector devices such as plotters, signage cutters, engraving machines, or variable spot size raster and gravur

13、e devices. Different shape representation techniques may vary in their ap- propriateness for different presentation devices. Bitmap representations describe the pattern of pels which are required for printing on raster devices. Bitmap glyph representations are less capable of being scaled or transfo

14、rmed in arbitrary ways while retaining a high standard of typographic quality. Bitmaps of glyph shapes can be represented either as ordered columns or rows of dots, or by a variety of schemes designed to provide more compact representations, particularly for larger sizes. 2 0 ISO/IEC ISO/IEC 9541-3:

15、1994(E) 1.6 Specification of glyph shapes (GSHAPES) Any font resource conforming to ISO/IEC 9541 and containing glyph shape information shall contain a GSHAPES property. GSHAPES is a property-list of shape-property-lists defining the sets of shape information associated with this font resource. shap

16、es-property-list := shapes-name, shapes-value-property-list shapes-name := STRUCTURED-NAME - ISO/IEC 9541-3/GSHAPES shapes-value-property-list := (tl-shape-property-list 1 property-list)* This architecture allows any glyph shape representation to be defined. The architecture for ISO/IEC 9541 Standar

17、d Shape Representation Type 1 is defined in section 2. 1.7 Extensions to the font interchange format ISO/IEC 9541 font information shall be interchanged using either the ASN.l or SGML forms defined in ISO/IEC 9541-2. These interchange formats include “markers” to include a definition for interchange

18、 formats for glyph shape information. These formats are defined in this clause with further definitions of the detailed format for each glyph shape representation included in equivalent clauses in each of the following sections. 1.7.1 ASN.l IS09541-GSHAPES 1 0 9541 3 0 ) DEFINITIONS := BEGIN IMPORTS

19、 Tl-Shape-Property-List FROM IS09541-GSTl ( 1 0 9541 3 0 0 ) Glyph-Shapes := SET tl-shape-property-list 0 EXTERNAL Tl-Shape-Property-List OPTIONAL, - see Section 2 of this part non-iso-properties 99 IMPLICIT Property-List OPTIONAL ) 1.72 SGML - ISO/IEC 9541-3:1994(E) 8 ISO/IEC Section 2: Type 1 glyp

20、h shape representation 2.1 Scope This section specifies the architecture and interchange format of one standard Glyph Shape Representation: ISO/IEC 9541 Standard TYPE 1. This representation technique is appropriate for, but not limited to, presentation on raster devices of low, moderate, and high re

21、solution. 2.2 Definitions The following definitions are specific to this section. 2.2.1 ciphertext: Information which has been encrypted. 2.2.2 current point: The last point referenced by a path-construction operator in the glyph description language; this point may be either the end point of the mo

22、st recently drawn line or curve or the point most recently pos- itioned by an rmoveto or setcurrentpoint operator. 2.2.3 encryption key: Integer number required for encrypting or decrypting a glyph procedure. 2.2.4 font program: A computer program incorporating a structured set of glyph procedures a

23、nd descriptive data. 2.2.5 ghost stem: An imaginary horizontal stem, applied only at the Max-Y and Min-Y extents of a glyph, for which an hstem hint operator must be specified if correct vertical alignment is required. 2.2.6 glyph procedure: A computer program written using the standard glyph shape

24、description operators de- fined in this section and represented in the interchange format defined herein. 2.2.7 glyph procedure interpreter: A computer process capable of interpreting a glyph procedure for the pur- pose of constructing an outline representation of the glyph and the associated data s

25、tructure required for scan conversion. 2.2.8 hint: A procedural or declarative specification of information additional to the geometric shape of a glyph, which aids in the preservation of proportions and features of that glyph during rasterizing for presentation on a raster device. 2.2.9 overshoot:

26、The part of a rounded or pointed glyph extremity which extends slightly beyond the position of flat-shaped extremities; used to achieve optically correct vertical alignment of glyphs for the horizontal writing mode. 2.2.10 path: A possibly disjoint set of subpaths and regions, constructed by one or

27、more path construction op- erators; the set of all subpaths in a glyph is a single path. 2.2.11 plaintext: Information which is not encrypted. 2.2.12 rasterization: A two-step process which involves determining the areas of a glyph which must be filled, and then creating a bitmap to represent those

28、areas. 2.2.13 region: A geometric area. 2.2.14 segment: The curve or straight line generated by a single graphics drawing command; the curve or straight line between consecutive points on the path defining a glyph shape. 2.2.15 snap: A mechanism for forcing a collection of glyph stems of varying nom

29、inal widths (in their device in- dependent outline representation) to convert to the same width when converted to a bitmap representation. 4 Q ISO/IEC ISO/IEC 9541-3:1994(E) 2.2.16 subpath: A sequence of connected straight or curved line segments constructed by one or more path construction operator

30、s. 2.2.17 typographic color: The relative boldness of the presented font; based on the relative width of the dom- inant type of stems in the font; also a comparative measure of the surface area of the presented glyph shapes relative to the area of the presentation surface. 2.3 Overview of Type 1 gly

31、ph shape representation architecture Type 1 glyph shape representation is an outline font representation which uses graphical drawing operators to describe the shape of a glyph. This approach has the advantage that the glyph can be scaled, rotated, and trans- formed in various ways, and can be raste

32、rized to create a bitmap for presentation. Properties defining glyph shapes may be either procedural constructs or additional declarative data defined at the font or glyph level. The glyph procedures may contain optional declarative hints. Hints consist of information in the font program which assis

33、ts the glyph procedure interpreter in preserving the proportions and features of a glyph as it is scaled and optimized for the pel grid of a raster device, but their usefulness is not limited to this application. Font-level hints may be defined for the entire font and help to control the alignment a

34、nd stem widths. Glyph-level hints apply only to the glyph in which they are defined, and primarily help to control the rasterization of vertical and horizontal stems. Glyph shapes are defined by procedural constructs and additional declarative data called properties. These addi- tional data help to

35、accomplish a variety of goals: General Properties help to identify the font program and the type of glyph shape representation used (see 2.6.1). Typographic color properties help to control the apparent weight of scaled and presented glyphs as well as to achieve uniform stroke widths (see 2.6.2). Gl

36、yph procedure properties primarily provide parameters and subroutines for use by glyph procedures (see 2.6.3). NOTE 2 Glyph shape representations which conform to this part of IS0 9541 constitute computer programs or procedures and as such may be subject to protection under laws covering intellectua

37、l property rights. This section defines the properties of glyph shapes in the following clauses: 2.4 explains Type 1 glyph shape concepts 2.5 explains the glyph procedure interpreter model 2.6 defines Type 1 glyph shape properties 2.7 defines glyph-level procedure semantics 2.8 defines the use of su

38、broutine procedures 2.9 defines the interchange format 2.4 Type 1 glyph shape concepts The following clauses explain concepts related to the Type 1 glyph shape technology. 2.4.1 Glyph coordinate system The Type 1 glyph shape technology uses a continuous glyph coordinate system as described in subcla

39、use 8.2 of ISO/IEC 9541-1:1991. NOTE 3 Throughout this section, any example value specified as a constant number of units is based on an assumption of a RELUNITS value of 1 000. 5 ISO/IEC 9541-3:1994(E) Q ISO/IEC 2.4.2 Glyph procedure language The glyph procedure language is used to specify glyph sh

40、apes and hinting parameters. This language allows the specification of one path, which may consist of multiple disjoint subpaths. After constructing the entire path, the glyph procedure interpreter causes the glyph to be filled or stroked as one entity, depending on the value of the PAINTTYPE proper

41、ty. 2.4.3 Glyph procedure interpreter The glyph procedure interpreter is a virtual machine (see 27.1) which interprets glyph procedures written in the glyph procedure language. 2.4.4 Alignment position An alignment position is a single position offset which refers to a y-coordinate at which glyph ex

42、tremities may align in the y direction. Alignment positions are only used in pairs to define alignment zones (see 2.4.8) for font re- sources with WRMODENAME values of LEFT-TO-RIGHT or RIGHT-TO-LEFT. A font resource with an ALIGNNAME value of BASE-ALIGN has its baseline on the x-axis. Alignment posi

43、tions are specified by the BLUEVALUES and OTHERBLUES font-level properties and are specified in pairs consisting of a flat and an overshoot position (see 2.4.5 and 2.4.6). Font resources with a WRMODENAME value of TOP-TO-BOTTOM, or an ALIGNNAME value of CENTRE-ALIGN, such as those containing East As

44、ian ideographic glyphs, generally have glyphs centered on a single alignment position (which need not be specified in the font), and do not have separate alignment positions for extremities of the glyph shapes. 2.4.5 Flat position A flat position is the alignment position to which primarily flat sha

45、ped glyph extremities align. The judgment as to what a flat shape is depends on an artistic decision by the typeface designer. Extremities which are judged to be almost flat may also be considered to be appropriate to align to a flat position. The concept of a flat position is not applicable to font

46、s with an ALIGNNAME value of CENTRE-ALIGN, or a WRMODENAME value of TOP-TO-BOTTOM. 2.4.6 Overshoot position The overshoot position is an alignment position associated with, and occurring just beyond, a flat position (see figure 11, to which non-flat glyph extremities may align. The purpose is to all

47、ow glyphs of various shapes to appear to align precisely, allowing for optical illusions, in the vertical direction. The overshoot position is not applicable to fonts with an ALIGNNAME value of CENTRE-ALIGN, or a WRMODENAME value of TOP-TO-BOTTOM. NOTE 4 Which glyphs require overshoots, and how much

48、 a glyph extremity extends past the flat position in the ideal outline representation, is a decision made by the typeface designer or developer. The Outline Modification and Intelligent Fill (rasterization) process (not part of this part of ISO/IEC 9541: see figure 7) may control these extensions so

49、 that the resulting bitmap representation exhibits correct vertical alignment for the required size of glyph and characteristics of the presentation device. 2.4.7 Overshoot suppression Overshoot suppression refers to a mechanism for not allowing overshoots to be rasterized at small sizes even though the scaling process might otherwise cause the overshoot features to round to one pel beyond the flat position. 2.4.8 Alignment zone An alignment zone is the area lying between two alignment positions-beginning at a flat position and extending to the maximum overshoot position of