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Xref: bloom-picayune.mit.edu comp.fonts:5966 news.answers:3313 Path: bloom-picayune.mit.edu!snorkelwacker.mit.edu!news.media.mit.edu!micro-heart-of-gold.mit.edu!wupost!spool.mu.edu!caen!nic.umass.edu!dime!dime.cs.umass.edu!walsh From: walsh@cs.umass.edu (Norman Walsh) Newsgroups: comp.fonts,news.answers Subject: comp.fonts FAQ: part 1 of 5 Summary: This posting answers frequently asked questions about fonts. It addresses both general font questions and questions that are specific to a particular platform. Message-ID: <WALSH.92Oct2140516@ibis.cs.umass.edu> Date: 2 Oct 92 18:05:16 GMT Expires: 6 Nov 92 00:00:00 GMT Sender: news@dime.cs.umass.edu Reply-To: walsh@cs.umass.edu (Norm Walsh) Followup-To: poster Organization: Dept of Comp and Info Sci, Univ of Mass (Amherst) Lines: 1005 Approved: news-answers-request@MIT.Edu Archive-name: fonts-faq/part1 Version: 1.0.0 --- [cut here] --- FAQ for comp.fonts: section 1, part 1 of 2 --- FAQ for comp.fonts: Part I: General Info Version 1.0.0, Release 02OCT92 Welcome to the comp.fonts FAQ. This article, posted monthly, describes many of the basic questions that seem to be repeated frequently on comp.fonts. Your comments are both welcome and encouraged. The FAQ is divided into sections. The first section is a general overview. The remaining sections are more-or-less platform specific. The FAQ is posted in pieces to avoid clobbering news and/or mail gateways that are incapable of handling arbitrarily large items. The sections are: Part I: General Info Part II: Macintosh-specific Info Part III: MS-DOS-specific Info Part IV: *nix-specific Info Part V: Sun-specific Info Part VI: NeXT-specifc Info Part VII: X-specific Info Part VIII: Font utilities Even if you don't use a particular architecture, you may find it helpful to read the FAQ for that platform at least once. Some ideas, like font format conversion, may be relevant to more than one platform even if they are expressed in platform-specific tools at this time. After the FAQ is more stable, monthly DIFFs will be posted as well as the complete FAQ. This section is divided into the following topics: 0. Notes about the FAQ 1. What's the difference between type 1 fonts, type 3 fonts, type 5 fonts, Macintosh fonts, Windows fonts, TrueType fonts, LaserJet fonts, etc. 2. Where can I get <> fonts. 3. Where can I get fonts for non-Roman alphabets. 4. How can I convert my <> font to <> format? 5. Are fonts copyrightable? 6. File Formats / Font Formats / Ligatures / Standard Fonts / Glossary 7. Bibliography / Other Resources 8. Rules of Thumb 9. Acknowledgements 10. A brief introduction to typography ------------------------------------------------------------------------------ 0. Notes about the FAQ. Words printed in single quotes 'like this' will someday appear in the glossary. The glossary doesn't contain very much right now. This convention isn't followed very thoroughly at present. If you notice something that should be marked or something you feel should be in the glossary, please let us know. All trademarks are the trademarks of their respective owners. Standard disclaimers apply. The FAQ is maintained by Norm Walsh <walsh@cs.umass.edu> and Bharathi Jagadeesh <bjag@nwu.edu>. 1. What's the difference between type 1 fonts, type 3 fonts, type 5 fonts, Macintosh fonts, Windows fonts, LaserJet fonts, etc. This question is not trivial to answer. It's analogous to asking what the difference is between various graphics image file formats. The short, somewhat pragmatic answer, is simply that they are different ways of representing the same "information" and some of them will work with your software/printer and others won't. At one level, there are two major sorts of fonts: bitmapped and outline (scalable). Bitmapped fonts are falling out of fashion as various outline technologies grow in popularity and support. Bitmapped fonts represent each character as a rectangular grid of pixels. The bitmap for each character indicates precisely what pixels should be on and off. Printing a bitmapped character is simply a matter of blasting the right bits out to the printer. There are a number of disadvantages to this approach. The bitmap represents a particular instance of the character at a particular size and resolution. It is very difficult to change the size, shape, or resolution of a bitmapped character without significant loss of quality in the image. On the other hand, it's easy to do things like shading and filling with bitmapped characters. Outline fonts represent each character mathematically as a series of lines, curves, and 'hints'. When a character from an outline font is to be printed, it must be 'rasterized' into a bitmap "on the fly". PostScript printers, for example, do this in the print engine. If the "engine" in the output device cannot do the rasterizing, some front end has to do it first. GhostScript, for example, rasterizes the page before it displays it on the screen. Many of the disadvantages that are inherent in the bitmapped format are not present in outline fonts at all. Because an outline font is represented mathematically, it can be drawn at any reasonable size without significant loss of quality (at least, the loss of quality is not a direct consequence of resizing it--any font printed at a small enough size shows a significant loss of quality as the size approaches the resolution of the device). Additionally, because it is rasterized "on demand," the font can be adjusted for different resolutions and 'aspect ratios'. LaserJet .SFP and .SFL files, TeX PK, PXL, and GF files, Macintosh Screen Fonts, and GEM .GFX files are all examples of bitmapped font formats. PostScript Type 1, Type 3, and Type 5 fonts, Nimbus Q fonts, TrueType fonts, and LaserJet .SFS files are all examples of outline font formats. Neither of these lists is even close to being exhaustive. To complicate the issue further, identical formats on different platforms are not necessarily the same. For example Type 1 fonts on the Macintosh are not directly usable under MS-DOS or Unix, and vice-versa. Henry Schneiker <reachable electronically?> created the following description of the differences between several scalable font technologies. It has been pointed out that the following description shows signs of its age (for example, the eexec encryption has been thoroughly hacked). I don't dispute the observation and I encourage anyone with the knowledge and time to submit a more up to date description. It has further been suggested that this commentary is biased toward Kingsley/ATF. The omission of details about Bitstream (and possibly Bauer) may be considered serious since their software lies inside many 3rd-party PostScript interpreters. The moderators of this FAQ would gladly accept other descriptions/ explanations/viewpoints on the issues discussed in this (and every other) section. *-[Quote]-----------------------------------------------------------* There has been a lot of confusion about font technologies in recent times, especially when it comes to Type 1 versus Type 3 fonts, "hints," PostScript compatibility, encryption, character regularizing, kerning, and the like. Encryption (eexec) All fonts produced with Adobe's font technology are protected through data encryption. The decryption is provided by the `eexec' (encrypted execute) PostScript operator and, until recently, was only present in Adobe's licensed PostScript. Recently, RIPS reverse-engineered the eexec operator and now provides it to its licensees. Other clone vendors are sure to follow. It is important to note that the eexec operator can be used to decrypt and execute any valid PostScript statement. Therefore, any PostScript program or program fragment may be encrypted so it will work with eexec operator. You will further note that eexec is not tied to fonts in any way. While eexec is mostly used to protect font data, it can be used to protect any PostScript code. It just so happens that Adobe's favorite thing to protect is font data. The eexec operator is also used to hide the methods for applying patches to the PostScript system and methods for gaining privileged access to protected procedures. There is no gain in speed by encryption. In fact, there is a slight speed penalty resulting from decryption. The encrypted data is also twice as big as unencrypted data. This is compensated for in Adobe fonts by storing the hexadecimal characters (cipher text) as binary on the host disk. Type 1, Type 3, and Type 5 font formats There are generally three font formats used in Adobe PostScript printers: Type 1, Type 3, and Type 5. Type 1 fonts are Adobe's downloadable format. Type 3 fonts are third-party downloadable format. Type 5 fonts are the ROM-based fonts that are part of your printer. There is no functional difference between a Type 1, Type 3, or Type 5 font. A Type 3 font can do anything a Type 1 or Type 5 font can do. The only real difference between them is where the `BuildChar' routine comes from. For Type 1 and Type 5 fonts it's built into the printer. For Type 3 fonts it's built into the font. In other words, anything a Type 1 font can do a Type 3 font can also do. When PostScript is asked to generate a character, PostScript looks in the font's dictionary for FontType. If FontType is 1 or 5 PostScript executes an internal routine that knows how to interpret the font data stored in CharStrings. If FontType is 3 PostScript executes the routine BuildChar from the font's dictionary to interpret the font data (often stored in CharStrings). However, each BuildChar routine is written to read data formatted in a method convenient to the vendor. Adobe, Altsys, Bitstream, and Kingsley/ATF all format their font data differently and, hence, have different BuildChar routines. The font data for Adobe's Type 1 font format is a binary representation of the outline font data. Kingsley/ATF also uses a binary representation of its Type 3 outline font data and stores the binary code as binary on the host disk. Both company's binary representation and store technique substantially reduces the storage requirements on the host and in the printer. Other vendors, such as Altsys and Bitstream, also use a binary encoding system for their Type 3 outline font data. However the data is stored on the host as hexadecimal text characters and requires about double the storage as the binary storage technique. It should be noted that a compact text encoding (an alternate Altsys format) requires two to three times as much storage space as the binary storage technique. Type 5 fonts are special in that they often include hand-tuned bitmaps for the commonly used sizes, such as 10- and 12-point. Other sizes are generated from the outlines in normal fashion. Type 3 fonts can also be used to implement other font outline systems, such as Sun's F3 and Apple's B-spline. Type 1 and Type 5 fonts can only be used with the Adobe font format. Also, don't confuse Type 1, Type 3, and Type 5 fonts with Bitstream's Type A, Type B, Type C, and Type F. They are not the same and serve only to confuse the issue. Resolution `hints' When a character is described in outline format the outline has unlimited resolution. If you make it ten times as big, it is just as accurate as if it were ten times as small. However, to be of use, we must transfer the character outline to a sheet of paper through a device called a raster image processor (RIP). The RIP builds the image of the character out of lots of little squares called picture elements (pixels). The problem is, a pixel has physical size and can be printed only as either black or white. Look at a sheet of graph paper. Rows and columns of little squares (think: pixels). Draw a large `O' in the middle of the graph paper. Darken in all the squares touched by the O. Do the darkened squares form a letter that looks like the O you drew? This is the problem with low resolution (300 dpi). Which pixels do you turn on and which do you leave off to most accurately reproduce the character? All methods of hinting strive to fit (map) the outline of a character onto the pixel grid and produce the most pleasing/recognizable character no matter how coarse the grid is. Adobe's hinting system relies on regularizing (equalization) and straightening out the original character outline as much as possible when the font is created. Unfortunately this process of modifying the original font outlines for the sake of low resolution can badly distort the character from its original design. These distortions are visible when printing at high resolution. This system also places limitations on the placement of end points in the outline, again for the sake of the hinting system. The new Fontographer hinting system (a subset of Nimbus-Q) places similar restrictions on the character outline. for instance, to make proper use of the hints, a character must be (re)drawn with curve end points at curve maximum/minimum X/Y extents. In order for strokes to be equalized to the same widths, they must be (re)drawn with exactly the same widths. Again, the shape of the character is ruled by the limitations of the hinting system. The hinting system used by Kingsley/ATF in ATF Type Designer I* is fundamentally different. It does not require special placement of curve and end points in order to function. It also does not require modification of the original font outline to aid in grid fitting or stroke equalization. Once the outline has been created to the artist's satisfaction the hints for stroke equalization and grid fitting are added without any modification to the character outline. The net effect is that the Kingsley/ATF system does not sacrifice high-resolution quality while achieving low-resolution quality. Character fill algorithms The fill algorithm in PostScript tends to turn on too many pixels and make a character fatter and wider by one or two pixels. This is especially obvious in small sizes at low resolutions. Both Adobe and Kingsley/ATF compensate for this, thus keeping characters to proper thickness. Other type vendors do not currently compensate for the fill algorithm and thus end up with undesirably heavy characters, which is particularly noticeable at small sizes. Optical Scaling* Optical Scaling modifies the relative shape of a character to compensate for the visual effects of changing a character's size. As a character gets smaller, the relative thickness of strokes, the size of serifs, the width of the character, the intercharacter spacing, and interline spacing should increase. Conversely, as a character gets larger, the relative thickness, widths, and spacing should decrease. Optical Scaling is used by Kingsley/ATF. Contrast this with linear scaling, in which all parts of a character get larger or smaller at the same rate, making large characters look wide and heavy (strokes are too thick, serifs are too big) while small characters look thin and weak. Linear scaling is used by Adobe, Altsys, Bitstream, and all other typeface manufacturers. The difference between linear scaling and Optical Scaling are clear, a difference even the untrained eye can see. The difference is particularly easy to see at high resolutions. Kerning As applied to PostScript fonts, kerning refers to kern pairs. A kern pair specifies two characters (e.g., A and V) and the distance to move the second character relative to the first. The typical use of a kern pair is to remove excessive space between a pair of characters. However, it may also be used to add space. How many kern pairs do you need? The answer depends on how well regular character spacing has been set and on the typeface itself. The better the default letterspacing has been set, the fewer kerning pairs are needed. In fact, an excessive number of kern pairs may be the artifact of a poor letterspacing job. The typeface itself has a lot to do with which characters may benefit from kerning. Just because one typeface has a kern pair does not mean the text typeface will need kerning for the same pair. Different typeface designs have very different kerning requirements. The moral to the story is: The number of kerning pairs is not a good quality indicator. PostScript clones There are currently several printer manufacturers on the market with PostScript clones. To be viable, a PostScript clone must comply with the `red book' (PS Language Reference Manual). The main problem the clones have is with fonts. Much of the font (and copy-protection) technology Adobe uses is undocumented. The eexec operator is not defined and Adobe protects its operations as a trade secret. Without the eexec operator Adobe fonts cannot be decrypted. There are many other operators like eexec, such as the internal BuildChar routine, that are required for proper operation of Adobe fonts, and these operators are also held as trade secrets. Without these operators, the Adobe font data cannot be interpreted. The clone problem can be approached from two directions. RIPS, a PostScript clone manufacturer, has reverse-engineered the eexec and other operators (including BuildChar and friends) and now sells a PostScript clone that is Adobe-compatible in all respects needed for proper interpretation of Adobe font data (Type 1 encrypted). Other companies are sure to follow. This is only important to users who have purchased or desire to purchase the Adobe/Linotype font library. The other way to solve the font technology problem is to implement your own. This is the route chosen by Altsys, Bitstream, Kingsley/ATF, and various other vendors. Some of the technologies used by these companies have been listed and compared. All these vendors use Type 3 unencrypted fonts, but the similarities end there. The technologies implemented from one company to the next vary in source of artwork, precision of digitization, availability and types of hints, Optical Scaling, storage requirements, and much more. Apple Royal (`sfnt') format and System 7 Apple's new System 7.0 will support a new format of outline font that will allow high-quality characters of any size to be displayed on the screen. The new format (`sfnt') stores font outlines as B-spline curves along with programmed resolution hints. B-spline curves are faster to compute and easier to manipulate than the Bezier curves used in PostScript. Adobe is not going to support Apple's new format by converting the Adobe/Linotype library to B-spline format. There are two reasons for this: First, there is no support for font encryption (yes, the hooks are there, but nothing is implemented). Second, Adobe does not want to dilute PostScript and its font library. However, the Macintosh is too big a market to simply turn away from. Therefore, Adobe will provide its Font Manager to display its own fonts on the Mac screen. K/A will provide its entire library in Apple's B-spline format in addition to various PostScript formats. Users will be able to pick whatever format is most convenient. The Adobe font license When you license Adobe's font technology you get a `black box' that takes your font data in a prescribed format and turns it into Adobe's format with hints (suitable for use by the Type 1 BuildChar routine) and encrypted fonts for use by the eexec operator. No capability is provided to create or edit font data or screen fonts. The Kingsley/ATF font license When you license Kingsley/ATF's font technology you get a complete state-of-the-art font digitization system (ATF Type Designer I*), with output capabilities for supporting many operating systems and formats, resolution hinting, Optical Scaling, kerning editor, automatic screen font generation, and screen font editor. Included is a sophisticated end-user font utility. You also receive assistance in converting your current font data into the ATF format for editing. The Altsys font method Altsys sells a font digitization system called Fontographer without further license. The new version supports a limited version of the Nimbus-Q hinting system, and includes a kerning editor, output for the Macintosh, and a screen font editor. The FontStudio method Letraset has purchased the FRed font editor and should be releasing it soon. It will be sold without further license. The URW font method URW designed the Ikarus system about 15 years ago. Due to the normally small size of artwork and the cross-hair pointer used in the digitization process, the accuracy of outlines generated with this system suffers. This is the same system used to generate the Adobe font outlines. They are currently marketing the Nimbus-R hinting system. ATF Type Designer I and Optical Scaling are trademarks of Kingsley/ATF Type Corporation. PostScript is a trademark of Adobe Systems Incorporated. Apple and Macintosh are trademarks of Apple Computer, Inc. Fontographer is a trademark of Altsys Corporation. Ikarus and Nimbus-R are trademarks of URW. FontStudio is a trademark of Esselte Pendaflex Corporation. *-[Unquote]---------------------------------------------------------* 2. Where can I get <> fonts. Before I go any farther, let me extol the virtues of the Archie servers. If you need to find something on the net, and you have any idea what it might be called, Archie is the place to go. In North America, telnet to "archie.rutgers.edu" and login as "archie". There are many other servers around the world, any Archie server can give you a list of other servers. There are better documents than this to describe Archie and you should be able to find them from the above starting point. If you have trouble, feel free to ask norm <walsh@cs.umass.edu> (via Email please, no need to clutter comp.fonts with a query about Archie ;-). In addition to the telnet option, several archie clients exist including a very nice XArchie implementation. Adobe Type 1 Fonts in MS-DOS/Unix Format: ftp.cica.indiana.edu:/pub/pc/win3/fonts ftp.cica.indiana.edu:/pub/pc/win3/fonts/atm archive.umich.edu:/msdos/mswindows/fonts Adobe Type 1 Fonts in Mac Format: mac.archive.umich.edu:/mac/system.extensions/font/type1 sumex-aim.stanford.edu:/info-mac/font Adobe Type 3 Fonts in Mac Format: mac.archive.umich.edu:/mac/system.extensions/font/type3 TrueType fonts in MS-DOS Format: ftp.cica.indiana.edu:/pub/pc/win3/truetype TrueType fonts in Mac Format: mac.archive.umich.edu:/mac/system.extensions/font/truetype TeX PK/PXL/GF fonts: The TeX community has it's own support groups that can provide better answers to this question. The canonical list of MetaFont fonts is posted occasionally to comp.text.tex. The comp.text.tex newsgroup (or the Info-TeX mailing list, if you do not have access to news) are good places to start. Email norm <walsh@cs.umass.edu> if you need more specific information. LaserJet bitmap fonts: wuarchive.wustl.edu:/pub/msdos/laser Also on other simtel20 mirrors... If you know of other archive sites (the above list is no where near complete) or other formats that are available on the net, please let us know. The sites above represent places where shareware and public domain fonts are available. Many, many typefaces are not available in shareware form. And many shareware faces are less than adequate for a variety of reasons, particularly at small sizes. It seems to be the consensus of the comp.fonts community that "you get what you pay for." If you need a professional quality font, you should probably buy it from a professional. A list of font vendors (annotated with information about non-Roman alphabets) was contributed by Masumi Abe <abe@adobe.com>. Masumi is Adobe's Manager of Typographic Marketing for Asia. [ed: as of 7/92] The list is quite long and it is posted separately. It can be retrieved via anonymous ftp from /pub/norm/comp.fonts on ibis.cs.umass.edu. 3. Where can I get fonts for non-Roman alphabets. As mentioned above, the list of font vendors is annotated with information about non-Roman alphabets. Commercially, Masumi <abe@adobe.com> suggests that Linguists' Software is the current [ed: as of 7/92] leading supplier of non-Roman fonts. 4. How can I convert my <> font to <> format? Conversion from one bitmapped format to another is not generally too difficult. Conversion from one scalable format to another is very difficult. Several commercial software packages claim to perform these tasks, but none has been favorably reviewed by the comp.fonts community. ATech's AllType program, in particular, has had poor reviews [ed: as of 7/92]. For specific conversions, check the platform specific parts of the FAQ. Most of the conversions discussed require platform specific tools. Here is a summary of the conversions discussed (and the section in which they appear): From To Notes ------------------------- ------------------------- ------------- Mac Type1 PostScript PC Type1 PostScript MS-DOS PC Type1 PostScript Mac Type1 PostScript Mac, commercial TrueType Type1 PostScript } No answer as Type1 PostScript TrueType } of 7/92 PC Type1 PostScript TeX PK MS-DOS TeX PK HP LaserJet bitmaps MS-DOS HP LaserJet bitmaps TeX PK MS-DOS TrueType HP LaserJet bitmaps MS-DOS, hack!! 5. Are fonts copyrightable? This topic is hotly debated at regular intervals on comp.fonts. Terry Carroll <tjc50@juts.ccc.amdahl.COM> provides the following analysis of current [ed: as of 6/92] legislation and regulation regarding fonts and copyrights. Members of the comp.fonts community are encouraged to submit other materials that add clarity to the issue. It has been pointed out that this section deals primarily font copyright issues relevant to the United States and that this situation is not universal. For example, in many parts of Europe typeface designs are protectable. *-[Quote]-----------------------------------------------------------* First, the short answer: Typefaces are not copyrightable; bitmapped fonts are not copyrightable, but scalable fonts are copyrightable. Authorities for these conclusions follow. Before we get started, let's get some terminology down: A typeface is a set of letters, numbers, or other symbolic characters, whose forms are related by repeating design elements consistently applied in a notational system and are intended to be embodied in articles whose intrinsic utilitarian function is for use in composing text or other cognizable combinations of characters. A font is the computer file or program that is used to represent or create the typeface. Now, on to the legal authorities: Volume 37 of the Code of Federal Regulations specifies this about the copyrightability of typefaces: "The following are examples of works not subject to copyright and applications for registration of such works cannot be entertained: . . . typeface as typeface" 37 CFR 202.1(e). By the way, you won't find that in the most recent (7/1/91) edition of the CFR; the addition was enacted 2/21/92. It'll be in the next edition, though. It's described in the 2/21/92 edition of the Federal Register, page 6201 (57 FR 6201). The change didn't actually change the law, it just clarified it, and codified existing Copyright Office policy. The regulation is in accordance with the House of Representatives report that accompanied the new copyright law, when it was passed in 1976: "The Committee has considered, but chosen to defer, the possibility of protecting the design of typefaces. A 'typeface' can be defined as a set of letters, numbers, or other symbolic characters, whose forms are related by repeating design elements consistently applied in a notational system and are intended to be embodied in articles whose intrinsic utilitarian function is for use in composing text or other cognizable combinations of characters. The Committee does not regard the design of typeface, as thus defined, to be a copyrightable 'pictoral, graphic, or sculptural work' within the meaning of this bill and the application of the dividing line in section 101." H. R. Rep. No. 94-1476, 94th Congress, 2d Session at 55 (1976), reprinted in 1978 U.S. Cong. and Admin. News 5659, 5668. It's also in accordance with the one court case I know of that has considered the matter: Eltra Corp. V. Ringer, 579 F.2d 294, 208 USPQ 1 (1978, C.A. 4, Va.). The Copyright Office holds that a bitmapped font is nothing more than a computerized representation of a typeface, and as such is not copyrightable: "The [September 29, 1988] Policy Decision [published at 53 FR 38110] based on the [October 10,] 1986 Notice of Inquiry [published at 51 FR 36410] reiterated a number of previous registration decisions made by the [Copyright] Office. First, under existing law, typeface as such is not registerable. The Policy Decision then went on to state the Office's position that 'data that merely represents an electronic depiction of a particular typeface or individual letterform' [that is, a bitmapped font] is also not registerable." 57 FR 6201. However, scalable fonts are, in the opinion of the Copyright Office, computer programs, and as such are copyrightable: "... the Copyright Office is persuaded that creating scalable typefonts using already-digitized typeface represents a significant change in the industry since our previous [September 29, 1988] Policy Decision. We are also persuaded that computer programs designed for generating typeface in conjunction with low resolution and other printing devices may involve original computer instructions entitled protection under the Copyright Act. For example, the creation of scalable font output programs to produce harmonious fonts consisting of hundreds of characters typically involves many decisions in drafting the instructions that drive the printer. The expression of these decisions is neither limited by the unprotectable shape of the letters nor functionally mandated. This expression, assuming it meets the usual standard of authorship, is thus registerable as a computer program." 57 FR 6202. *-[Unquote]---------------------------------------------------------* 6. File Formats / Font Formats / Ligatures / Standard Fonts / Glossary 6.1. File Formats Many different kinds of files are available on the net. These files contain many different kinds of data for many different architectures. Frequently, the extension (trailing end) of a filename gives a good clue as to the format of its contents and the architecture that it was created on. In order to save space, most files on the net are compressed in one way or another. Many compression/decompression programs exist on multiple architectures. Multiple files and directories are often combined into a single 'archive' file. Many archive formats perform compression automatically. 6.1.1. File Format Extensions .tar Unix 'tape archive' format. Tar files can contain multiple files and directories. Unlike most archiving programs, tar files are held together in a wrapper but are not automatically compressed by tar. .Z Unix 'compress' format. Compression doesn't form a wrapper around multiple files, it simply compresses a single file. As a result, you will frequently see files with the extension .tar.Z. This implies that the files are compressed tar archives. .hqx Macintosh 'BinHex' format. In order to reliably transfer Mac files from one architecture to another, they are BinHex encoded. This is actually an ascii file containing mostly hexadecimal digits. It is neither a compression program nor an archive wrapper. .sit Macintosh 'Stuffit' archive. .cpt Macintosh 'Compactor' archive. Like the .tar.Z format that is common among Unix archives, Macintosh archives frequently have the extensions .sit.hqx or .cpt.hqx indicating a BinHex'ed archive. .arc PC 'arc' archive. This is an older standard (in PC terms, at least) and has gone out of fashion. .zip PC 'zip' archive. This is the most common PC archive format today. .arj PC 'arj' archive. .zoo PC 'zoo' archive .lzh PC 'lha/lharc' archive. 6.2. Font Formats Just as the are many, many archive formats, there are many different font formats. The characteristics of some of these formats are discussed below. Once again, the file extension may help you to determine the font type. (On the Mac, the resource TYPE field is (probably) a better indicator). PostScript Type 1 Fonts: Postscript Type 1 fonts (Also called ATM (Adobe Type Manager) fonts, Type 1, and outline fonts) contains information, in outline form, that allows a postscript printer, or ATM to generate fonts of any size. Most also contain hinting information which allows fonts to be rendered more readable at lower resolutions and small type sizes. PostScript Type 3 Fonts: Postscript type 3 fonts are an old outline font format that is not compatible with ATM. Most developers have stopped using this format except in a few special cases, where special type 3 characteristics (pattern fills inside outlines, for example) have been used. TrueType Fonts: Truetype fonts are a new font format developed by Microsoft with Apple. The rendering engine for this font is built into system 7 and an init, the Truetype init, is available for system 6 (freeware from Apple). It is also built into MS Windows v3.1. Like PostScript Type 1 and Type 3 fonts, it is also an outline font format that allows both the screen, and printers, to scale fonts to display them in any size. Bitmap Fonts: Bitmap fonts contain (surprise) bitmaps of fonts in them. This a picture of the font at a specific size that has been optimized to look good at that size. It cannot be scaled bigger without making it look horrendously ugly. On the Macintosh, bitmap fonts also contain the kerning information for a font and must be installed with both type 1 and type 3 fonts. Their presence also speeds the display of commonly used font sizes. 6.2.1. Font Format Extensions .afm Adobe Type 1 metric information in 'ascii' format (human parsable) .bdf Adobe's Bitmap Distribution Format. This format can be converted to the platform specific binary files required by the local X Windows server. This is a bitmap font format distributed in ASCII. .chr Borland stroked font file .gf TeX graphic font bitmap font file .mf TeX MetaFont font file (text file of MetaFont commands) .pfa Adobe Type 1 Postscript font in "ascii" format (PC/Unix) I believe that this format is suitable for directly downloading to your PostScript printer (someone correct me if I'm wrong ;-) .pfb Adobe Type 1 PostScript font in "binary" format (PC/Unix) Note: this format is not suitable for downloading directly to your PostScript printer. There are utilities for conversion between PFB and PFA (see the utilities section of the FAQ). .pfm Printer font metric information in Windows format .pk TeX packed bitmap font file .ps Frequently, any PostScript file. With respect to fonts, probably a Type3 font. This designation is much less 'standard' than the others. .pxl TeX pixel bitmap font file .sfl LaserJet bitmapped softfont, landscape orientation .sfp LaserJet bitmapped softfont, portrait orientation .sfs LaserJet scalable softfont 6.3. Ligatures A ligature occurs where two or more letterforms are written or printed as a unit. Generally, ligatures replace characters that occur next to each other when they share common components. Ligatures are a subset of a more general class of figures called "contextual forms." Contextual forms describe the case where the particular shape of a letter depends on its context (surrounding letters, whether or not it's at the end of a line, etc.). One of the most common ligatures is "fi". Since the dot above a lowercase 'I' interferes with the loop on the lowercase 'F', when 'f' and 'i' are printed next to each other, they are combined into a single figure with the dot absorbed into the 'f'. An example of a more general contextual form is the greek lowercase sigma. When typesetting greek, the selection of which 'sigma' to use is determined by whether or not the letter occurs at the end of the word (i.e., the final position in the word). Amanda Walker <amanda@visix.com> provides the following discussion of ligatures: Ligatures were originally used by medieval scribes to conserve space and increase writing speed. A 14th century manuscript, for example, will include hundreds of ligatures (this is also where "accents" came from). Early typefaces used ligatures in order to emulate the appearance of hand-lettered manuscripts. As typesetting became more automated, most of these ligatures fell out of common use. It is only recently that computer based typesetting has encouraged people to start using them again (although 'fine art' printers have used them all along). Generally, ligatures work best in typefaces which are derived from calligraphic letterforms. Also useful are contextual forms, such as swash capitals, terminal characters, and so on. A good example of a computer typeface with a rich set of ligatures is Adobe Caslon (including Adobe Caslon Expert). It includes: Upper case, lower case, small caps, lining numerals, oldstyle numerals, vulgar fractions, superior & inferior numerals, swash italic caps, ornaments, long s, and the following ligatures: ff fi fl ffi ffl Rp ct st Sh Si Sl SS St (where S=long s) [Ed: Perhaps a more common example is the Computer Modern Roman typeface that is provided with TeX. this family of fonts include the ff, fi, fl, ffi, and ffl ligatures which TeX automatically uses when it finds these letters juxtaposed in the text.] While there are an infinite number of possible ligatures, generally only the most common ones are actually provided. In part, this is because the presence of too many alternate forms starts reducing legibility. A case in point is Luxeuil Miniscule, a highly-ligatured medieval document hand which is completely illegible to the untrained eye (and none too legible to the trained eye, either :)). There is no "complete" set of ligatures. 6.4. Standard Laser Printer Fonts Postscript printers with 17 fonts have: Courier, Courier-Bold, Courier-BoldOblique, Courier-Oblique, Helvetica, Helvetica-Bold, Helvetica-BoldOblique, Helvetica-Narrow, Helvetica-Narrow-Bold, Helvetica-Narrow-BoldOblique, Helvetica-Narrow-Oblique, Helvetica-Oblique, Symbol, Times-Bold, Times-BoldItalic, Times-Italic, Times-Roman Postscript printers with 35 fonts have: All of the above, plus the following: ZapfChancery-MediumItalic, ZapfDingbats, AvantGarde-Book, AvantGarde-BookOblique, AvantGarde-Demi, AvantGarde-DemiOblique, Bookman-Demi, Bookman-DemiItalic, Bookman-Light, Bookman-LightItalic, NewCenturySchlbk-Bold, NewCenturySchlbk-BoldItalic, NewCenturySchlbk-Italic, NewCenturySchlbk-Roman, Palatino-Bold, Palatino-BoldItalic, Palatino-Italic, Palatino-Roman HP LaserJet printers (II, IIP) Courier 10, Courier 12, LinePrinter 16.66, ... HP LaserJet printers (III, IIIP) All of the above, plus the following: Scalable Times Roman, Scalable Univers 6.5. Glossary [ I ripped this right out of the manual I wrote for Sfware. If you have comments, improvements, suggestions, please tell me... ] baseline The baseline is an imaginary line upon which each character rests. Characters that appear next to each other are (usually) lined up so that their baselines are on the same level. Some characters extend below the baseline (``g'' and ``j'', for example) but most rest on it. More technically: The baseline is the invisible line around which character images are positioned. A sequence of characters is usually aligned, when rendered, according to the baseline. For example, an English 'A' sits on top of the baseline, while 'g' extends both above and below the baseline." bitmap A bitmap is an array of dots. If you imagine a sheet of graph paper with some squares colored in, a bitmap is a compact way of representing to the computer which squares are colored and which are not. In a bitmapped font, every character is represented as a pattern of dots in a bitmap. The dots are so small (300 or more dots-per-inch, usually) that they are indistinguishable on the printed page. character A character is an individual symbol in a font. The letter ``A'' is a character. So is a period. All of the printed symbols that can appear in a font are characters. They can also be called glyphs. More technically: (1) The smallest component of written language that has semantic value. Character refers to the abstract idea, rather than a specific shape (see also glyph), though in code tables some form of visual representation is essential for the reader's understanding. (2) The basic unit of encoding for the Unicode character encoding, 16 bits of information. (3) Synonym for "code element". (4) The English name for the ideographic written elements of Chinese origin. download Downloading is the process of transferring information from one device to another. This transferral is called downloading when the transfer flows from a device of (relatively) more power to one of (relatively) less power. Sending new fonts to your printer so that it ``learns'' how to print characters in that font is called downloading. font A font is a collection of symbols that have similar characteristics. The symbols in a font have a fixed typeface, size, weight, style and symbol set. For example, upright, bold Times Roman at 10pt is a font. Contrast with typeface. More technically: A particular collection of characters of a typeface with unique parameters in the 'Variation vector', a particular instance of values for orientation, size, posture, weight, etc., values. The word font or fount is derived from the word foundry, where, originally, type was cast. It has come to mean the vehicle which holds the typeface character collection. A font can be metal, photographic film, or electronic media (cartridge, tape, disk). glyph A glyph is a more general term for a symbol that can appear in a font. Usually we refer to individual symbols in a font as characters (because they are things like ``A'' and ``&''). However, since any arbitrary smear of ink can occur in a font, a more general term is sometimes used. More technically: (1) The actual shape (bit pattern, outline) of a character image. For example, an italic 'a' and a roman 'a' are two different glyphs representing the same underlying character. In this strict sense, any two images which differ in shape constitute different glyphs. In this usage, "glyph" is a synonym for "character image", or simply "image". (2) A kind of idealized surface form derived from some combination of underlying characters in some specific context, rather than an actual character image. In this broad usage, two images would constitute the same glyph whenever they have essentially the same topology (as in oblique 'a' and roman 'a'), but different glyphs when one is written with a hooked top and the other without (the way one prints an 'a' by hand). In this usage, "glyph" is a synonym for "glyph type," where glyph is defined as in sense 1. hints When a character is described in outline format the outline has unlimited resolution. If you make it ten times as big, it is just as accurate as if it were ten times as small. However, to be of use, we must transfer the character outline to a sheet of paper through a device called a raster image processor (RIP). The RIP builds the image of the character out of lots of little squares called picture elements (pixels). The problem is, a pixel has physical size and can be printed only as either black or white. Look at a sheet of graph paper. Rows and columns of little squares (think: pixels). Draw a large `O' in the middle of the graph paper. Darken in all the squares touched by the O. Do the darkened squares form a letter that looks like the O you drew? This is the problem with low resolution (300 dpi). Which pixels do you turn on and which do you leave off to most accurately reproduce the character? All methods of hinting strive to fit (map) the outline of a character onto the pixel grid and produce the most pleasing/recognizable character no matter how coarse the grid is. kerning Kerning refers to slight changes in the spacing between characters. Some letter combinations (``AV'' and ``To'', for example) appear farther apart than others because of the shapes of the individual letters. Many sophisticated word processors move these letter combinations closer together automatically. outline font/format See 'scalable font' scalable font A scalable font, unlike a bitmapped font, is defined mathematically and can be rendered at any requested size (within reason). softfont A softfont is a bitmapped or scalable description of a typeface or font. They can be downloaded to your printer and used just like any other printer font. Unlike built-in and cartridge fonts, softfonts use memory inside your printer. Downloading a lot of softfonts may reduce the printers ability to construct complex pages. symbol set The symbol set of a font describes the relative positions of individual characters within the font. Since there can only be 256 characters in most fonts, and there are well over 256 different characters used in professional document preparation, there needs to --- [cut here] --- FAQ for comp.fonts: section 1, part 1 of 2 ---