2 Everything About Printer

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The Basics of Printers

Ev er y t hingYou Want ed t o Know

About Pr int er s


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To t he ReaderIn the past few years, the number of printer users has climbed rapidly as a result ofthe spread of the personal computer. Printers come in all sorts of types and models

from simple family printers to the high resolution printers used by designers oreditors. Internally, they are all different and so are their printing capabilities.This book attempts to explain the basics of printers and their relationship with

computers in a way that should make it easy for beginners to understand. Ofcourse, not everything to do with printers is covered herein, but knowing the basicsof how printers work and printing in general should help towards solving newquestions and problems.

How This Book is Or ganizedThis book is divided into Basics and Technical Information. As the title suggests,Basics provides general information about printers. On the other hand, TechnicalInformation explains in greater detail the technical matters and terminologypresented in the first part of the book. The book has been organized this way sothat reading through it all will help the printer student to progressively build up his

understanding of printers. Technical matters have also been addressed individuallyto enable quick reference on anything the reader wants to know or is having troubleunderstanding.

Copyr igh ts Microsoft, MS, MS-DOS and Windows are registered trademarks of Microsoft

Corporation in the US. Macintosh, KanjiTalk, AppleTalk, LaserWriter, LocalTalk, QuickDraw and TrueType

are registered trademarks of Apple Computer, Inc. in the US. IBM is a registered trademark of IBM Corporation in the US. PC-98 is a trademark of NEC Corporation.

Pentium is a registered trademark of Intel Corporation in the US. Other names of companies, hardware and software used in this publication are

the trademarks, registered trademarks or registered product names of their

respective companies.

Standard symbols and are not used in this book.


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Table o f Cont ent sBasics

Chapter 1 What is a Printer?......................................... 3

Chapter 2 Types of Printers ..........................................7

Printers by Their Mechanical Features....................7

Printers by Printed Color .......................................15

Printers by Printer Language ................................16

Printers by How They Are Used ............................20

Chapter 3 Printer Construction ..................................25Ink Jet Printer ........................................................25

Laser Printer ..........................................................28

Chapter 4 Printing Process......................................... 31

Data Processing ....................................................32

Processing on Computer .......................................33

Sending Print Data ................................................39

Technical Infor mat ion1. PDL and GDI .................................................................51

PDL .......................................................................51

GDI ........................................................................ 58

2. Text and Fonts..............................................................61

Character Set ........................................................61Typeface ................................................................62

Typestyle ...............................................................62

Size .......................................................................63

Orientation .............................................................64

3. Graphics ....................................................................... 65

Bitmapped Graphics ..............................................65

Vector Graphics .....................................................65


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Gradation Processing ............................................66

4. Printer Controller .........................................................73

Spooling ................................................................ 74Buffering ................................................................75

Rasterizing ............................................................75

5. Printer Interface ...........................................................77

Parallel Interface ................................................... 77

Serial Interface ......................................................81

AppendixGlossary ...........................................................................87

Index ................................................................................. 93


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W h at is a p r i nt e r ?

Basics


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Chapter 1


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Chapter 1 What is a Pr int er ?

A printer is a machine that prints out data processed on a com-

puter. When the graphics and text processed on the computer aresent to the printer, the printer translates the data and prints it out.

Language

Commands

Images

Post cardsName Cards

In-house/Neighborhood flyersTransparency film

Printed matter

Most of the time, data is printed on plain paper, but printing can be

done on labels, transparency film and other media, too. Printouts

can of cause be in black-and-white though a recent popular trendis the full color printer which renders a near-photographic picture

quality. Also, with all the computer networking going on these days,

it is no longer rare to see an office setup with multiple computersconnected to a single printer.

Printers today are being widely used for everything from printing

postcards and personal documents to commercial uses such as

DTP (desk top publishing).


DTP See p. 88.


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Chapter 1

Printers are used in all sorts of environments such as the home and office.

Depending on the objective at hand, one computer can be connected to one

printer or multiple computers can share a single printer. Printers are selectedand used according to the specific environment and objectives.

When used by just one person

In this configuration, one computer is connected to one printer. Generally, the

connection is made with a Centronics cable between the printer port on the

computer and the interface port on the printer. However, the type of cable and

the configuration of the connectors will differ according to the computer and

printer. (Centronics See p. 78.)

When connected to the printer port of the computer in the above configuration,

the printer is referred to as a local printer.

* The interface generally complies with IEEE 1284 and, when not, IEEE 1394 or

some other standard. (IEEE 1284 See p. 79. IEEE 1394 See p. 82.)

When used by many persons in a network

In this configuration, a single printer is used with multiple computers which

themselves are connected to a network. Generally, this is the kind of

configuration used in offices and schools. Using one printer for multiple

computers is called sharing (the printer). And, a printer which is used via a

network is called a network printer. Printers can be shared in one of two basic

ways: one is to use the local printer of a computer connected to a network as a

network printer, while the other is to directly connect the printer to the network.

Printer Environment

Centronics (parallel interface)* cable, etc.


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When a local printer is used as a network printer

In general, a Centronics cable is used to connect a computer to the printer. The

computer connected to the printer must also be connected to the network. The

computer is set up for sharing the printer. In this way, a local printer can be

used as a network printer.

When a printer is connected directly to a network

A network cable* is used to connect the printer to the network. The printer must

be network compatible, that is to say, equipped with a network port such as a

10BASE-2 or 10BASE-T port. (10BASE-2 and 10BASE-T See p. 87.)

* In an Ethernet LAN, a 10BASE coaxial cable is generally used for the network

connection. This 10BASE coaxial cable is of simple construction and is tough

against noise. It is used in LANs where the transmission speed is between 10

kbps and several Mbps. However, the cables must be kept short because

signals weaken considerably over long distances.

It is also possible to connect multiple printers to multiple computers and, from

within this configuration, select a printer according to a specific purpose.

* There are also 10BASE-5, 10BASE-2 and other standards. (10BASE-5 See

p. 87.)

Hub(Centralconnecting

device)

10BASE-TCable*, etc.

Centronics (parallel interface) cable, etc.


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Chapter 1

Data processed on the computer is sent to the printer and printed out there.

This data will differ according to the type of printer. To keep the explanation

simple for now, see the outline. For more information, see Chapter 4 PrintingProcess.

Sending an image to the printer

The selected image is prepared as bitmap data on the computer and sent to the

printer. This image is sent as binary data which describes the image to be

printed. (Binary data See p. 90.) The printer can understand this data, but

people cannot read it. This approach generally brings down the cost of the

printer, but it also increases the burden placed on the computer. However, the

printing speed can be made faster by increasing the computer processing

capacity.

Two typical graphic printing systems are GDI and QuickDraw. (GDI See p. 17

and 58. QuickDraw See p. 17.)

Commands

Other than text and graphics, the computer sends commands which instruct the

printer tofor exampleposition text or graphics. Because printer controldepends on commands, when intricately laid out document data is sent, the

image on the screen and that of the printout may differ.

Two typical printer control command systems are ESC/P and PCL. (ESC/P

See p. 17. PCL See p. 16 and 51.)

Language

The data to be printed is sent to the printer in language format. The program

which controls the printer is sent to the printer in a readable format (text file).

This data can be saved as a file and manipulated by the user. In general,printing is done via a dialog between the computer and the printer. The typical

printer control language is PostScript. (PostScript See p. 16 and 54.)

Data Sent from the Computer to the Printer

Language

Commands

Images


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Types o f p r i n te r s

Chapter 2 Types of Pr int er sThe printer is constantly being improved in terms of performance,

price, printing quality and other aspects which users demand. As a

result, many types have been developed with diverse mechanisms,printing techniques, data processing techniques and other features.

Many printers are in use today, but they can be categorized by theirmechanical features, printed colors, printer language, etc.

Pr int e r s by Thei r M echanical Feat u r esWhen categorized by mechanical features, printers are roughly

divided into impact printers and nonimpact printers. Then, thesetwo types are further divided into other types.

Printers bymechanicalfeatures

Impactprinter

Nonimpactprinter

Characterprinter

Thermaltransfer printer

Thermal printer

Electrostatic printer

Electro-photographicprinter

Dot matrix printer

Daisy wheel printer

Thermal wax transfer printer

Thermal dye transfer printer

Laser printer

LED printer, LCS printer

Ink jet printer Thermal jet printer

Piezoelectric printer

Drum line printer

Im pa c t pr i nt e r sPrinters which hit the print medium are called impact printers.

Working on the same principle as the typewriter, they have existed

for a long time. A typewriter has keys that look a lot like those of a

computer keyboard. Pressing a key hammers the character for that

key onto the paper. Because an ink ribbon (thin strip of cloth

impregnated with ink) is stretched between the paper and the

character, the ink is transferred to the paper and printed there. Impactprinters use either one of two basic printing techniques: character

printing with which the characters themselves are printed or dot

matrix printing with which dots are printed until eventually forming

a character. With both techniques, printing is loud and the printoutis not so clear. Nevertheless, because continuous form paper can

be used, this technique is still used today to print out program source

codes and data lists.


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Chapter 2

s Character printing

This printing technique is based on the principle of the typewriter.

In fact, the print mechanism is exactly the same as that of the

typewriter. When a key is pressed, the character of that key is

hammered onto the paper. An ink ribbon (thin strip of cloth

impregnated with ink) is stretched between the paper and the

character, so the ink is transferred and printed on the paper ashammering goes on. With character printers, a daisy wheel on which

the characters have been arrayed in a radial pattern rotates as

characters are selected. The characters are then hammered ontothe paper with a hammer. This type of printer is called a daisy

wheel printer, while there are also other types such as drum line

printers which have sped up the printing process.

Drum

Character

Ribbon

Paper

Hammers

[Advantages]

Continuous form and heat-sensitive multipart form can be used.

[Disadvantages] Only the loaded font can be used.

Printing is slow.

Printing is loud.

s Dot matrix printing

In this technique, characters are printed as a matrix of dots, thus

the name. However, the print head is not shaped like a matrix. The

print head is a row of needle pins called wires. The wires are

moved and hammered to print the dots on the paper. The dots

eventually build up the character. The wires are selected using


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electric signals from the computer. This technique offers more

freedom compared to character printing because the latter is only

capable of printing the provided characters. Hence, more characters

and fonts can be printed with a dot matrix printer. Moreover, if a lot

of wires are arrayed into a line, the whole line can be printed at the

same time. Also, the clarity of the character can be enhanced by

increasing the number (density) of wires per character.

Spring

Movable block

Electromagnet

Needle pin

Needle pin

Ink ribbon

Paper

Example characterprintout

[Advantages]

Continuous form and heat-sensitive multipart form can be used.

[Disadvantages]

There is a limit to the number of usable fonts.

Printing is slow.

Printing is loud.

Because the character is composed of dots, printed characters

have rough contours.


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Chapter 2

Some impact printers can print in color. The print head is the same as that used

for monochrome printing, but color is achieved by working with the ink ribbon. In

this case, the ink ribbon has a wide band and is impregnated with cyan, magenta,yellow and black. By changing the angle of the ribbon cassette, the printed color

is changed.

Color Printing on Impact Printers

Printers can also be categorized by the amount of data printed at a time or print

unit. In this case, they are serial printers, line printers and page printers.

Serial printer

The data received from the computer is printed out sequentially one character at

a time. One character is printed each time the print head passes from left to right

or vice-versa. Because the mechanism is simple, the printer is compact and low-

priced. On the other hand, printing speed is proportional to the speed at which the

print head travels, so this kind of printer is not apt for high speed.

Line printer

The data received from the computer is printed out sequentially one line at a time.

Because each pass of the print head prints a full line, it is faster than a serial

printer. However, as in the case of a drum line printer, the print head must be

large enough to contain a full line, therefore it does not lend itself to downsizing

very well. But, with an ink jet printer, the print head for a full line is not necessary,

so you do see smaller printers.

Page printer

The data received from the computer is printed out in a batch one page at a time.

Generally, the same electrophotographic technique applied with copiers is used.

Printing is very fast.

Printers by Print Unit

abcdeABCDE12345abcdeABCDE12345

abcdeABCDE12345

abcdeABCDE12345

abcdeABCDE12345abcdeABCDE12345

abcdeABCDE12345


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Nonimpac t p r i nte r sNonimpact printers use heat or other scientific means to print text

and graphics, so there is no direct contact between the print head

and print medium. Some nonimpact techniques are thermal printing,

electrophotography, ink jet, thermal transfer and electrostatic

printing. All of these are quiet and render sharp clarity, thus

nonimpact printing is the mainstream in printers today.

s Thermal printing

Similar to thermal facsimiles, printing is done by heating the print

head (thermal head) and transferring this heat to a heat-sensitive

paper. The principle is basically the same as thermal transfer. Moreinformation can be found in Everything You Wanted to Know About

Facsimiles.

[Advantages]

The print mechanism is simple in construction, so printers are

low-priced and highly reliable.

[Disadvantages]

Paper yellows when exposed to sunlight.

Plain bond paper cannot be used.

s Electrophotographic printing

This technique uses a photoconductor similar to that employed in

copiers. It prints one full page at a time in contrast to the onecharacter or one line of impact dot matrix printers and other typesof nonimpact printers. Compared to other techniques, the

mechanism of optical section and data processing circuitry are more

complex and sophisticated, but printing is high speed and highquality. Laser, LED and LCS printers are all electrophotographic

printers, but they differ in the way the light is projected on the drum.

Otherwise, they are similar in construction and principle, so they

cannot really be differentiated from their outward appearance.

Laser printing

In this technique, a laser draws the image on a photosensitive drum.

Toner is then applied to the drum and subsequently transferred to

the paper. Heat is required to fix the image on the paper, so powerconsumption is high. Before, this type of printer was expensive, so

it was not used by the average family. However, recently, new

models consume less power and cost less money, so the numberof personal laser printer users has started to grow.

Thermal transfer

printing

See p. 13.

LED and LCS

printing

See p. 12 and 89.

Laser printer

See p. 28.


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Chapter 2

LED and LCS printing

With LED (Light Emitting Diode) printing, thousands of tiny LEDs

are arrayed side-by-side into a row. When lit, the light is projected

through a lens and directly onto a photoconductor to form an

electrostatic latent image. With an LCS (Liquid Crystal Shutter)

printer, a matrix of liquid crystal dots which act as tiny shutters is

used instead of a laser beam. The electrostatic latent image isformed on the photosensitive drum by turning the shutters ON/OFF.

Both of these techniques are without the moving parts needed for

scanning, so their construction is simpler than that of a laser printer.

[Advantages]

Printing is high speed and high quality.

[Disadvantages]

Power consumption is high. It is more expensive than other popular types of printers.

s Ink jet printing

Printing is done by spraying ink droplets onto the paper. The principle

is very simple. Because of this and a comparatively simple

mechanism, printing costs are low and high quality color printoutsare quick and easy. It is also quiet and fast, thus it is the most

popular type of printer with personal users today. In addition to the

ink spraying technique, there are also thermal jet and piezoelectrictechniques.

Thermal jet printing

In this technique, the ink chamber is heated to form bubbles in the

ink. The ensuing pressure is what sprays the ink. The ink and heater

are housed in a small box (ink chamber) with a small hole in it. As

electric current is applied to the heater, the temperature rises. The

ink thus boils which makes the bubbles. As a result, pressure inside

the ink chamber rises and forces the ink out through the hole.

Piezoelectric printing

A piezoelectric device changes shape (elongates) when an electricvoltage is applied to it. This technique uses such a device to spray

ink. The ink is in a small box with a hole in it. The piezoelectric

device is mounted near the box. A voltage is applied to the deviceand it elongates whereby pressing the wall of the box inward. This

drives up the pressure inside the box and squirts the ink out through

the hole.

Ink jet printer See p. 25.

LCS See p. 89.


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[Advantages]

Printing is quiet.

Printouts are high quality.

Printing is fast, though not as fast as a laser printer.

Printers are inexpensive.

[Disadvantages] Ink runs when printed on plain bond paper.

The nozzle through which the ink is sprayed can clog.

s Thermal transfer printing

This technique applies a heated print head to an ink coated ribbon.

The ink melts and is transferred to the paper. A special type of

paper is needed to ensure quality printouts, but it is also possible to

print on plain bond paper because a ribbon is used. Heat-sensitive

paper can be used as well, in which case an ink ribbon is not needed.For color printing, ribbons are coated with cyan, yellow, magenta

and black ink. From a mechanical perspective, the process is very

similar to thermal printing. Nowadays, because of the popularity of

ink jet printers, thermal transfer printing is not seen much except

perhaps with portable word processors. In any case, it is the choice

of many design studios because it does offer high density colorprinting and the printer itself costs less than electrophotographic

printers.

ThermalheatprinterThermal heat print

Thermalhead

Thermal head

Paper

Ribbon

Print

Ribbon cartridge


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Chapter 2

[Advantages]

Printing is quiet.

Photographic-grade printouts can be obtained with special paper.

Printing can be done on plain bond paper.

[Disadvantages] Blurring occurs with plain bond paper.

Printing costs are high, especially with color printing, becausedisposable ribbon cartridges are used.

s Electrostatic printing

In this technique, the image is formed by impressing a special type

of paper with an electrical charge and then applying toner to it. The

toner is then transferred to the paper. The technique is often used

with plotters and not so often with general printers.


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Pr int e r s by Pr int ed Co lo rIn terms of printed colors, printers are divided into monochromeand color printers. The former prints only in black, while the latter

can print anywhere from 2 to 4 or more colors. The colors areprovided as ink, toner or ink ribbons.

Printers byprinted color

Monochrome printers

Colorprinters

2-color printers

Limited-colorprinters

Full-colorprinters

Monochr ome p r i nte rThis kind of printer prints only one color using ink, toner or an ink

ribbon. Shades are expressed by changing the size of the printeddot so as to form a gradation. For this reason, photographs comeout like a black-and-white photograph.

Co lo r p r i nte rColor printers print anywhere from 2 to 4 or more colors using ink,toner or an ink ribbon. There are two basic ways to represent colors:

one is to change the color itself according to the location on the

paper while the other is to mix colors into a new color.

s 2-color and limited-color printer

These printers change the color according to the print location.

Gradation is possible with all colors, but since colors are not mixed,

printouts are limited to those colors in the printers ink, toner or ink

ribbon.

s Full color printer

Full color printers both apply gradation and mix primary colors cyan,

yellow and magenta plus black. As a result, many colors can beexpressed and color photographs are printed out in full color. For

more information on color expression in printing, see EverythingYou Wanted to Know About Color Copiers.

Gradation

See p. 66 and 70.


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Chapter 2

Pr in te r s by Pr inte r LanguageTo print something out, the printer translates the commands andprograms sent from the computer, feeds the paper, and moves the

print head, drum and other parts. These commands and programsfrom the computer are referred to collectively as the printer

language. Language which describes one full page of information

is called page description language (PDL). There are many forms

of printer language from those specified as de facto standards to

those developed by individual manufacturers.

Printers by printerlanguage

Manufacturer-specificprinter languages

Other

GDI

QwickDraw

ESC/P

ESC/Page

PC-PR

NPDL

LIPS

Epson FX

Xerox Diablo 630

IBM ProPrinter

HPGL

HP PCL

Adobe PostScript

PCLPCL is short for Printer Control Language. It was developed byHewlett-Packard. Though originally intended as printer language

for controlling dot matrix and ink jet printers, it has since been

modified for use with laser printers. Several variations are out todaysuch as PCL3, PCL4 and PCL5e.

Pos tSc r iptPostScript is a printer language for laser printers developed byAdobe Systems. It was first developed for Apples LaserWriter, but

it is so widely diffused that now printers which use it to translate

commands into printer machine language are called PostScript

printers. PostScript comes in Level 1 and Level 2, and the release

of a PostScript 3 has been announced.

PostScript See p. 54.

PCL See p. 51.


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GDIGDI stands for Graphics Device Interface and is the graphics

display system in Microsoft Windows. What it does is to output the

data on the display to the printer. A printer which prints out the data

created by GDI is called a GDI printer.

Hereafter in this book, GDI is used to indicate the system whichcontrols display graphics and image output in a Windows

environment, while GDI language indicates the printer language

of the GDI feature.

Quick Dr awQuickDraw is the graphics display system built into the MacOS of

Apples Macintosh computer. Like GDI, QuickDraw outputs the data

which MacOS has on the display to the printer. Printers

which print out data created by QuickDraw are called QuickDrawprinters.

Manufac tu r e r -spec i f ic p r i nte r l anguagesEpson, Canon, NEC and other printer manufacturers have eachdeveloped their own printer languages. A few of them are introduced

herein.

s ESC/P

This printer language is from Epson. Because Epsons dot matrixprinters are used all over the world, ESC/P is also in that particular

field.

s ESC/Page

This is a printer language which Epson developed for page printers.

s PC-PR

This printer language was developed by NEC for PC-PR dot matrix

printers including thermal transfer types. This printer languagespread across Japan with the PC-98 series, but not overseas.

s NPDL

This is a printer language for page printers developed by NEC.

s LIPS

This is Canons printer language for page printers. It is the most

widely diffused printer language in Japan because of the popularity

of the LaserShot printer.

GDI

See p. 58.


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Chapter 2

Others FX

FX is a printer language that controls dot matrix printers of Epsons

FX series. Since these dot matrix printers have been around for a

long time and are used all over the world, most software supports

these printers. There is a version for laser printers which emulatesthe old Epson FX-80 and another which is compatible with the FX-

80. Still yet, another type emulates the high speed and

multifunctional FX-800.

s Diablo 630Diablo 630 was developed by Xerox to control their Diablo 630

daisy wheel printer. Diablo 630 was a de facto standard for

business documentation for a long time and was widely used by

printer manufacturers everywhere. Being a daisy wheel printer, theDiablo 630 cannot print out graphics. Also, because of the limited

number of fonts, today it is used only on old word processors.

s ProPrinter

ProPrinter is the printer language which IBM developed for their

dot matrix printers of the ProPrinter series. This series offers the

same performance as Epsons FX series, but it uses all character

sets (including special characters for drawing lines and boxes)

displayable on IBM compatible computers. ProPrinter is used in

unison with graphics display functions of IBM compatibles, whichimproves printing with graphics.

s HPGL

HPGL is short for Hewlett-Packard Graphics Language. It is widelyused with pen-plotters to produce industrial drawings. It is a de

facto standard language today because many plotter manufacturers

have emulated it. Also, many laser printers which offer HPGL

emulation are available today because most pen-plotters are slow

which means more time is needed with intricate drawingsnoisy

and difficult to set up. These printers emulate the HP7475A desktop

plotter and are used to draft-print drawings. Most laser printers do

not print in color and cannot take the large size paper that plotters

normally do. Resultingly, they are used only for printing drafts. For

design of PCB, etc., laser printers are given preference over plotters.

HPGL2 incorporates Hewlett-Packards PCL5 printer language and

offers PCL with capability of handling vector graphics.

Draft-print See p. 88.

Vector

graphics

See p. 65.


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Back before computers really became popular, it was often a case of one printer

per computer like a Printer for PC9801 or a QuickDraw Printer for Macintosh.

Consequently, it basically was not possible to connect to a computer of othermanufacturers and print something out. Nevertheless, the spread of the computer

has brought with it many new printers which can connect to practically any type of

computer regardless of the OS it runs on, and print out data accordingly.

As a result, even the same kind of printer uses a different name when connected

to some other type of computer or OS. For example, a printer might be called a

GDI printer when connected to a computer which runs Windows, but then it

would be called a QuickDraw printer when connected to a Mac. A PostScript

printer as well can operate as a GDI printer or a QuickDraw printer depending on

the computer setting. So, unlike categorizing printers by mechanical features or

printed colors, you cannot really categorize them by printer language.

Printer Languages and Types of Printers


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Chapter 2

Pr int e r s by How They Ar e UsedThe growing popularity of the computer has changed the system

environment. Printers are now being used in many different ways

such as one printer connected to one computer or multiplecomputers connected to one printer. Then, there are design studios

and publishing companies which use them in still other ways.

Basically, a printer capable of certain things is now being used in

different ways depending on what the users purpose is.

Printers by howthey are used

Local printers

Network printers

Proof printers

As a plotter

Printers byuser objective

Printers byenvironment

Pr i nte r s b y e nv i r o nm en ts Local printer

This configuration connects one printer to one computer. The

connection on the computer side is made through the printer port.

It often is the case today that a Centronics cable is used for theconnection. Using a switch, the printer can be connected and usedwith multiple computers, but it cannot simultaneously print out data

from more than one computer.

Centronics (parallel interface)* cable, etc.

* The interface generally complies with IEEE 1284 and, when not,IEEE 1394 or some other standard.


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Centronics cable, etc.

SwitchCentronics cable, etc.

s Network printer

A network printer prints out data sent via a network. The printer can

be either connected directly to the network or to a computer whichis on the network. In the latter case, the printer appears from the

configuration as if it is a local printer, but it can print out data sent

from other computers in the network by sharing.

Hub(Central

connectingdevice)

10BASE-Tcable, etc.

Centronics (parallel interface) cable, etc.

* There are also 10BASE-5, 10BASE-2 and other connectionstandards.


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Chapter 2

Pr i nte r s b y u s er o bj ec t i v es Proof printer

Computers are everywhere in the publishing and printing industries.

Its easy to understand how computers are used to do the image

setting and blocking, but what is interesting is that they are used to

make plates, a job which requires skill. Another recent advent isthe CTP (Computer To Plate) system which directly outputs data

prepared on computer to the printing plate. Simpler printers are

being used to print out draft copies for proofing. Hence, printers

used in this manner are called proof printers. What is featured

most about proof printers is that they support the larger paper sizeslike A2 and even bigger. Typical printers take up to A3 at best, but

in CTP, printouts are often on A2 or larger size paper.

Hub(Central

connectingdevice)

Imagesetter

A2A0 plain bond paper

Centronics orSCSI cable

Proof printer

s As a plotter

A plotter is a machine for printing out drawings. It uses a completely

different kind of control system than a printer. Nonetheless, because

of the high price and slow printing speed, it is being superseded by

the printer to some extent. Though a printer cannot express line

thickness in units of less than one point, it is inexpensive and fast,

thus it is used for printing out drawings that do not require a highdegree of accuracy. The data processed by a plotter is represented

in a totally different way than that processed by a printer, so usually

a technique known as emulation is used to enable printouts froma printer. Emulation is a technique by which the software and

Centronics,

SCSI

See p. 78, 80.


27/10423


Printerdriver

To printer

Page imagedescribedin HPGL

Converts commandsand program intoprinter language.

Computer

hardware functions are mimicked by the controlling system. In this

case, the printer emulates the plotters capabilities.


28/10424

Chapter 2


29/10425

Pr i nt e r Co ns t r u c t i on

Chapter 3 Pr int er Cons t r uc t ion

Printers are constructed in many different ways, so for simplicitys

sake, only the ink jet printer and laser printer will be discussed

herein.

Ink J e t Pr int e rThe ink jet printer prints by spraying ink onto the paper. The ink is

sprayed as droplets from many small nozzles on the print head and

forms a dot when it hits the paper. The image is thus composed by

drawing with these dots. The printer is simple in construction and,

because it offers good quality, fast printing at a comparatively lowprice, demand is growing especially on a backbone of individual

users. It is highly capable of reproducing color photographs and

the most recent models even come with neutral tint ink in addition

to the primary colors cyan, yellow and magenta, and black. Also,several different techniques for spraying the ink are available

amongst todays ink jet printers, of which piezoelectric printing and

thermal jet printing are two examples.

A

C

DG

F

E

B

CENTRONICS

A: Paper feed tray

When printing starts, the paper which is set here is drawn into

the printer. Gears and other parts drive the rollers which move

the paper through the printer. The feeling process is precision-controlled to prevent skewing and mispositioning at the print

head. The printer in the above illustration has a paper feed tray,

but there are types that use a paper cassette.


30/10426

Chapter 3

B: To computer cable ports

The cable which connects the printer to the computer is

connected to this port. There are many kinds of cable connectors,

but recently many types have a built-in bidirectional parallel

interface that conforms to IEEE 1284.

C: Ink cartridgeThis cartridge contains the ink used for printing.

D: Paper eject sectionPrintouts are ejected from here.

E: Print head

The print head sprays the ink onto the paper. It moves to the left

and right as printing proceeds. Usually, a belt is used to move

the print head. In color printing, many colors are produced byoverlapping several of the cartridge colors, therefore many short-

step passes are needed. For this reason, the print head is

controlled to a very high degree of precision.

F: Cleaner

To keep the print head from clogging or dripping ink on the paper,the print head is cleaned here prior to printing.

G: CapWhen no printing is going on, the print head hides in this area

underneath a cap. This prevents clogging in the print head by

keeping the ink from drying.

IEEE 1284 See p. 79.


31/10427


Piezoelec t r i c p r int ingA piezoelectric device changes its volume when impressed with an

electric voltage. This property is used to spray ink. First, a voltage

is applied to the piezoelectric device. In response, it expands and

presses against the wall of the ink chamber. Inside the chamber,

pressure rises hence forcing the ink out through a nozzle.

Piezoelectricdevice

Print head

Ink chamber

Paper

NozzleInk supply

Ink is sprayedonto the paperusing the way apiezoelectricdevice changesshape whenimpressed withvoltage.

Ther ma l je t p r i nt i ngA thermal jet printer has a small heater in the ink chamber. It warms

the ink to a boil. This boiling produces bubbles which drive uppressure in the ink chamber, and subsequently, shoots the ink out

through a nozzle.

Ink chamber

Heater

Ink chamber

Heater

Air bubble producedunder heat


32/10428

Chapter 3

Lase r Pr int erThe laser printer is one type of page printer. Data is sent over fromthe computer in lots of one page. Using a laser beam, the printer

forms an electrostatic latent image on a photoconductor. Then,applying toner to this image and transferring it to the paper produces

the printout. The mainstream in laser printers today is to print in

black-and- white, but demand is continually growing for color laser

printers, too. For more information on printing with digital laser

printers and how parts work, see Everything You Wanted to Know

About Facsimiles, or for details on color, see Everything You

Wanted to Know About Color Copiers.

M it as DP-56 0 on t he out s ideB

C A

A: To computer cable port

The cable which connects the printer to the computer is

connected to this port. It is basically the same situation as with

ink jet printers, but with high-speed printers, a SCSI interface is

sometimes built-in.

B: Paper feed section

When printing starts, the paper which is set here is drawn into

the printer. There are both hand-fed types and cartridge types.

Basically, laser printers are the same as ink jet printers in this

aspect, but the former is a page printer which prints out data inunits of one page, while the latter advances the paper only one

line at a time. This feature keeps the paper flowing continuously

from when the paper is first fed into the printer until the printout

is ejected.

C: Paper eject section

Printouts are ejected from here.


33/10429


M it as DP-56 0 on t he ins ide

A

C

B

D

E

A: Paper feed section

B: Laser unit

This unit controls and emits the laser beam which forms theelectrostatic latent image on the surface of a photoconductive

drum. It consists of a semiconductor laser, collimator lens,

polygonal mirror, F lens, cylindrical lens, BD sensor, reflecting

mirrors and other parts.

C: Imaging unit

This unit prepares the toner that is applied to the drum and applies

it. This toner forms the physical image which is later transferred

to the paper. The unit consists of a developing unit, drum and

main charger.

D: Transfer charger, charge erasing sectionThis unit electrically transfers the toner image on the drum to

the paper and, after transfer, neutralizes the charge on the drum

surface, referred to as cleaning.

E: Fixing unit

Using heat and pressure rollers, this unit fixes the transferred

image on the paper.

Later on in this book are provided explanations as to the basic

functions and construction of laser printers.


34/10430

Chapter 3


35/10431

Pr in t i ng Pr ocess

Chapter 4 Pr int ing Pr ocess

Data that has been created with application software (word

processing, graphics, etc.) on a computer is converted for printingin the following order.

For example, with MS Word, this data has a *.doc format

or, with Illustrator, it is *.ai. Usually, the image displayed on

the screen is printed out. Printing is executedwith

Windows for exampleby selecting the Print command in

the File menu.

1. The user creates the data on computer.Application-specific data

When the print command is executed, the OS checks

which printer has been selected and converts the data for

use on that printer. This data varies according to the type

of printer used, but in general, it is one of the following

three types.

Bitmapped data (The format depends on the printer.) Data displayed on the screen (The format depends on

the OS.)

Printer language (PCL, PostScript, etc.)

2. The user executes the print command.Data for the connected printer

A printer represents text and graphics as a matrix of dots.

Consequently, no matter kind of data is to be printed out,

the last step in the printing process is to convert the datainto dot data of the printer's resolution. This dot data is

referred to as a bitmap.

3. The printer creates a page image.Bitmapped data

In the above process, the conversion from step 1 to 2 is done throughthe computer. However, processes between steps 2 and 3 can be

either done from the computer or by the printer itself, depending on

the type of printer. This conversion from step 2 to step 3 is calledrasterizing.

This chapter explains the technology that has been introduced to

print data which has been processed on computer.

Rasterizing

See p. 75.


36/10432

Chapter 4

Data Pr ocess ingThe printer prints out the data from the computer, so certain data is

sent from the computer to the printer. However, the way in which

this data is processed for printing differs according to the type of

printer. In any case, this data, in the instant that it is handed overfrom the computer to the printer, can be roughly categorized into

the following three formats.

s When the computer sends bitmap data

This is a technique adopted with some GDI and QuickDraw printers

which are incapable of converting data from the computer intobitmap data. Most of the data processing is handled by the computer,

so the electric mechanisms of the printer can be simplified. This

kind of printer is called a sleek printer.

Application

Display system function Bitmap image

OSdisplaysystem

Printer driver Printer controller Printer engine

Computer Printer

s When the computer sends on-screen data

This technique is adopted with GDI and QuickDraw printers whichare capable of rasterizing the data from the computer. Because

rasterizing is done by the printer, it is possible to boost computer

performance and thus increase printing speed. This kind of printer

is said to be an intelligent printer.

Application

Display system function Bitmap image

OSdisplaysystem


Computer Printer

Printer controller

See p. 73.

Printer driver

See p. 35.


37/10433


sWhen the computer sends printer language

In this case, the computer sends data that can control the printer. It

is sent as language. The printer translates this language and

rasterizes it into a bitmap. This technique is adopted by PostScript

printers, for example. Printers which are controlled by printer

language are called PDL printers.

Application

Display system function Printer language Bitmap image

Computer Printer

OSdisplaysystem


Pr ocess ing on ComputerWhen the print command is executed, the computer starts the

process of sending the data in the application software to the printer.

The processing which the computer does will vary according to thetype of printer connected to it.

For PDL pr inte r s

The print data is converted into printer language by the computerand then sent to the printer. The printer translates the language,

rasterizes it as a bitmap and then prints it out. Two well-known

printer languages are PCL and PostScript.

Rasterizing

PrintingPrinterdriver

PDLexecutionsystem

Framebuffer

PrinterComputer

Page imagedescribed byOS displaysystem

Convertsdata from theapplicationinto PDL.

Frame buffer See p. 89.


38/10434

Chapter 4

[Advantages]

The printer language created by the computer has nothing to do with the type of

OS. No matter what OS is used, the printer language is created in the formatspecified for printing. Thus, a PDL printer does not depend on the system and,

consequently, can be connected to various types of computers. Also, since the

print data is sent to the printer in command format, the printer only needs to

handle a small amount of data, which means high-speed printing is possible.

[Disadvantages]

With PDL printers, TrueType fonts are processed as graphics, so there are no

built-in fonts. What this means is that the PDL printers ability to simply describe

the fonts and font data stored on the printers hard disk cannot be used inprinting. Moreover, it is necessary that both the computer and printer support the

same fonts; if one doesnt, the clarity of the printout is not guaranteed. (TrueType

See p. 42.)

Advantages and Disadvantages of PDL Printers

For GDI/Qu ickDr aw pr int e r sGDI is the graphic display system used by Windows, whileQuickDraw is that for the Macintosh. GDI printers receive and print

out the data displayed on the computers screen. The same

processing is done with a QuickDraw printer. There are two printing

processes with GDI printers. One is to send the prepared data

directly to the printer in GDI format and have the printer bitmap it.

The other is to have the computer rasterize the GDI data into a

bitmap before sending it to the printer. In both cases, the printer is

still called a GDI printer, but generally it is this latter when people

make reference to a GDI printer. This book also bases GDI printer

explanations on the latter.

Page image

described by GDI

Rasterizing

PrintingPrinterdriver

Framebuffer

PrinterComputer


39/10435


[Advantages]

With printers that have the computer handle everything up through rasterizing, the

printing mechanism can be made simple and inexpensive. Besides, computerswhich run on Windows or MacOS can be connected to any type of printer

regardless of who made it.

[Disadvantages]

When the computer does the rasterizing, its CPU becomes slow and, if it has

insufficient RAM, there is always the possibility of overrun or overflow errors being

generated. Also, printing speed depends entirely on the computers data

processing speed, so printers today are generally low speed. (RAM See p. 91.

Overrun error and overload error

See p. 90.)

Advantages and Disadvantages of GDI/QuickDraw Printers

Wha t t h e p r i nte r d r iv e r d oe sIt is not possible to print out data from a computer by simply

connecting the printer and computer with a cable. The printer cannot

be used unless the computers OS has a program for controllingthe printer and sending data to it. This program is known as a printer

driver and it must be registered with the OS.

Application

OS

Interface

Printer driver


40/10436

Chapter 4

The function of the printer driver varies according to the OS and

printer. Nevertheless, the basic responsibilities are to teach the

computer the functions (supported PDL, fonts and hardware

features) of the connected printer and to convert the print data into

a format compatible with the connected printer. The printer drivers

for the three most popular OSs on the market tokay are described

below.

s With MS-DOS

Until Windows became the norm, MS-DOS was the most widelyused OS in the world. Because the major applications running on

MS-DOS directly control the printer, the OS does not need a printer

driver. Accordingly, the printer has to be set up from within the

application. The same must be done with the rasterizer and fonts,

because they too are managed by the application. Nonetheless,

MS-DOS has its own printer driver, but because it cannot controlprinter functions for printing bold typeface characters, outline fonts

or drawing lines, printer control is handled by the application.

Font dataRasterizing

Application A

Rasterizing

A A

A A

B B

Application B

Font data

A: Both of the applications have a rasterizer of its own and outputtext and graphics to both the printer and display.

B: Fonts are also controlled by each of the applications and output

via the rasterizer to both the printer and display.


41/10437


sWith Windows

With Windows, the printer driver was moved to the OS. It is set up

from the Windows platform; setup need not be done through the

application as was the case with MS-DOS. By setting up the printer

with Windows, the printer can be used with any application. The

rasterizer and fonts which were functions of the application in the

MS-DOS environment are now a part of Windows and can be easilyaccessed from the application.

Windows uses its GDI to display text and graphics on the screen

as well as to send that data to the printer. At the start of the printingprocess, GDI creates the raster data and transfers it directly to the

printer. This has made high quality printing possible without

depending on the printer. Also, regarding fonts, Windows supports

TrueType, as part of the standard software. Collectively, Windows

calls their printing system the Windows Printing System or WPS

for short.

Application A Application B

OS (Windows)

Rasterizing Driver

Font data

Applicationplatform

Systemplatform

B

BB

BA

A: Font management and rasterizing are handled by Windows.

B: The application only commands Windows to draw something on

the screen or print it out on the printer.


42/10438

Chapter 4

When the Windows printing system first came out, it was met with complaints that

printing was too slow, it wasnt truly WYSIWYG* and printer setup was too

complicated. To solve these problems, Microsoft announced their MicrosoftWindows Printing System in 1992. Later on, the system was incorporated into At

Work, another Microsoft concept to link computers and office equipment, and

debuted as the At Work Printing Software (AWPS). AWPS was composed of a

printer driver, printer interface and page description language, and it drew the

attention of many users for the way it improved the Windows printing environment

through faster printing and an easier user interface. However, AWPS never

became popular, so the name was reverted back to WPS and so it is used today.

* WYSIWYG is short for What You See Is What You Get, meaning the image on

the screen should be the same as the image on the printout.

About WPS

s With MacOS

MacOS is the operating system which Apple uses in their personal

computer, the Macintosh. Much before other companies, Appleincorporated a graphical user interface (GUI) into their system.

Because this greatly enhanced operability and the users power of

expression, it is widely used in the design, music and DTP fields.

They named the Japanese version of the system KanjiTalk. In

any case, it is nowadays referred to as simply MacOS regardlessof the applied language. The printer driver explanation that follows

will be based on KanjiTalk 7.5.1.

The Macintosh always goes through its built-in graphic display

system QuickDraw to display text or graphics on the screen or to

print something out. Internally, the printer driver is divided into a

printing manager and low-level driver. The former controls

printing, while the latter sends requests from the printing managerto the printer. When the printing process starts, the printing manager

creates the raster data which is then sent to the printer via the low-

level driver. This makes high quality printing possible withoutdepending on the printer.

Regarding fonts, the Macintosh generally uses PostScript fonts.

The use of TrueType fonts has increased recently, but because

generally Postscript printers are used for DTP, PostScript fonts are

used more often.


43/10439


Application

QuickDraw

Printer driver

Printing manager

Low-level driver

Printdialog box

Paper Setupdialog box

Sending Pr int Dat aThe data processed on computer is sent via the printer port and

cable to the printer. Documents usually consist of text and

illustrations, but the way in which they are reproduced differs: inthe case of text, by the type of character used, while in the case of

graphics, by the type of application which created the graphics.They also differ according to the type of printer.

This part of the book explains from where and how the text and

graphic data is sent to the printer. For more information on theinterface functions and standards used in the data transfer described

herein, see 5. Printer Interface in Technical Information.

Tes t t r ans fe r and r epr oduc t i onA set of characters is called a font. Fonts are usually stored ineither the computer or printer. Every time they need to be displayed

on the screen or printed out on paper, they are called up from

memory. Fonts are basically divided into the following two types.

Bitmapped fonts (Dot fonts)

Outline fonts


44/10440

Chapter 4

s Bitmapped fonts

Bitmapped characters are represented in dots. The size of a

character is specified in units of dots such as 16 x 16 or 24 x 24

dots. Consequently, a different font is required for each size. For

example, data for a single font consists of three files, one each for

10 point, 12 point and 24 point characters. Other sizes (14 or 20

point) specified by an application are displayed and printed byenlarging or shrinking the font data of the nearest size. The

processing done within the application enlarges and shrinks each

specific dot, so the displayed or printed characters come out with arough contour. Bitmapped fonts were used in printing when impact

dot printers were in vogue, but they are used less these days now

that ink jet printers and laser printers are more widely diffused and

outline fonts are supported by the OS.

Usually, the font data for a bitmapped font is stored in the computer.

In the printing process, it is sent to the printer as a bitmapped imageand so printed out.

Bitmapped font

Character printedin bitmapped font

1. Print command is executed.2. Print data is created with bitmapped font.3. Image data is sent to the printer.

4. Image data is converted by the frame buffer.5. Printing starts.


45/10441


s Outline fonts

This kind of font is used by specifying the logic address assigned to

the outline of the font. Because it is represented as a logic address,

it is completely independent of the printers resolution. Also, because

the font is treated as logic, enlargement, reduction, styling and

rotation can be done freely. Two well-known examples of outlined

fonts are TrueType fonts and PostScript fonts.

TrueType and PostScript differ in terms of file makeup and data

flow in the printing process.

Resolution

See p. 91.

Logic address See p. 89.


46/10442

Chapter 4

Printing with TrueType fonts

Both the font data displayed on the computer screen and that used

in printing are stored in a single file. For this reason, a single file

can be, in the case of a Japanese font, several MB or, in the case

of a European font, several tens of KB. TrueType fonts are rasterized

at the display or print resolution and sent to the screen or printer as

graphic data. This makes the characters appearing on the screenor in the printout sharp and clear.

TrueType font

Character printedin outline font

Character displayedin outline font

4. Image data is converted bythe frame buffer.

5. Printing starts.

1. Print command is executed.2. TrueType font is treated as

graphic data.3. Image data is sent to the printer.

Printing with PostScript fontsThe font data displayed on the computer screen is stored in the

computer, whereas that used for printing is in the printer. Dot fonts

are used for displaying characters on the screen, while outline fonts

are used in printing. In the printing process, the name of the font

used is described in the print data (PostScript data) and sent to theprinter. Reading this name, the printer loads the corresponding font

data to its memory and uses it in printing.

PostScript is a page description language developed by Adobe Systems. Though

it describes the image of an entire page, it is referred to herein as one type of

printer outline font. Moreover, PostScript is actually composed of bitmapped fonts

for displaying characters on the screen and outlined fonts for printing. Because it

has these printer outline fonts, it is treated as an outline font in this book.

About PostScript Fonts


47/10443



PostScript

screen font

Character displayedin bitmapped font

1. Print command is executed.

2. PostScript file is created.

3. PostScript file is sent to the printer.

4. PostScript file is translated.

5. Data is converted by the frame buffer.

6. Printing starts.

Another point is that PostScript fonts use a utility known as Adobe

Type Manager (ATM) which sharply displays characters on screen

and, in the event the printer does not have the necessary font data,prints characters out clearly.

ATM is composed of an ATM program and ATM compatible

fonts.When used, font data is stored in the computer and sent in

the print data to the printer in the printing process. Fonts areproduced sharp and clear both on the screen and in printouts.

However, only ATM compatible fonts are outlined with ATM.

ATM font

Character displayedin outline font


5. PostScript file is translated.

6. Data is converted by the framebuffer.

7. Printing starts.

1. Print command is executed.

2. Outline data of ATM compatiblefont is created.

3. PostScript data is created,4. PostScript data is sent to the

printer.


48/10444

Chapter 4

Smoothing is a technique that focuses on the relationship of adjoining dots. It

corrects this relationship by changing the position and size of the dots. To

understand how it works and why it is used, first realize that a printer converts theprint data into a digital space known as a memory address. Even data

expressing freely drawn curves and lines is eventually converted into dots at the

rasterizing process. In other words, even with outlined fonts, additional dots

cannot be printed between two other dots if the printers resolution is too low for

that, and so the character will come out with a jagged contour. This is where

smoothing comes into play. It smoothes the jaggedness by changing the position

and size of the dots, so the final resolution as printed is higher than the actual

resolution of the printer. In the below illustration, only the position of the dots has

been corrected, but the size is changed as well when working with curves. In thisway, resolution of a 300 dpi printer can be boosted to the equivalent of 600 dpi.

Smoothing differs according to the printer. But, all techniques are based on the

relationship of adjoining dots. For example, illustrations and characters have dots

in some sort of continuous series, so smoothing is easy. However, with

photographs, dots are completely random which makes it difficult to correct the

data. In this case, a high resolution printer is needed.

More information on smoothing can be found in Everything You Wanted to Know

About Facsimiles.

Smoothing

Data as createdon screen

Enlargement of arrow Smoothed data

Il lu s t r a t io n t r a ns fer a nd r e pr o du c t io nIllustration data handled by computers is called graphic data. Aswith text, the graphic data from an application is converted into

printer applicable data, bitmapped and printed.

Graphic data is composed of that intended for screen display and

that for printing, and it is stored in a single file. In this respect, it is

something similar to a TrueType font. When the print command is

executed, print data which corresponds to the data displayed on

the screen is sent to the printer.


49/10445


Graphic data can be either a bitmapped graphic or a vector graphic.

The printing process differs depending on which type it is. In this

section, it is explained how both types of data are processed and

printed. For more information on bitmap graphics or vector graphics,

see 3. Graphic Data in Technical Information.

s Bitmapped graphicsLike with bitmapped fonts, bitmapped graphics are represented with

dots. When the print command is executed, the data corresponding

to the data displayed on the screen is sent directly to the printer. Itis then converted to the resolution of the printer and printed out.

Image data read from a scanner and screen shots (data created

with Windows by pressing PrintScreen, or the Shift + Command +

3 keys with MacOS) are all bitmapped graphics. Bitmapped graphics

can be BMP, TIFF, Windows Metafile, PICT, EPS or other type.

s Vector graphics

Vector graphics are like print data for outlined PostScript fonts in

that coordinates for the start and end points of a line and the

thickness of the line are represented as a numerical formula. When

the print command is executed, the data corresponding to the data

displayed on the screen is transferred directly to the printer. There,the numerical formulas are translated and converted into bitmapped

data of the printers resolution, and then printed out.

Vector graphics can express smooth flowing lines as well as thethickness of free-drawn lines. That is why application software that

creates vector graphics is absolutely essential for many designers

and illustrators. Vector graphics include, amongst others, PostScript

and HPGL.

Co lo r r epr esen ta t i onWith the spread of the Macintosh and Windows, color printers have

been faced with newer and more sophisticated demands. Recently,

even the most basic type of printer renders pictures and color

photographs of rather good quality. Though the printer can print out

what is displayed on the computer screen, colors come out different.

You have probably heard tell of the three primary colors of light

and the three primary colors of color. Here, the situation will be

looked at from the computers side. The principles of color are also

discussed in Everything You Wanted to Know About Color Copiers,

so you can also look there for more information.

Bitmappedgraphics

See p. 65.

Vectorgraphics

See p. 65.


50/10446

Chapter 4

s How colors are represented on screen

The three primary colors of light are as follows.

R (Red) :Complement of cyan (C)

G (Green) :Complement of magenta (M)

B (Blue) :Complement of yellow (Y)

The process of changing the intensity of these three colors and

mixing them to express another color is called additive mixing.

TVs and monitors project color pictures by this technique. Bychanging the gradation of the three primary colors, full color display

is possible.

In general, full color means it is possible to express approximately

16 million colors. With full color, 8 bits are assigned to each R, G

and B, so colors are represented with 24 bits.

s How colors are represented in printing

The three primary colors of color are as follows.

C (Cyan) :Complement of red (R)

M (Magenta) :Complement of green (G)

Y (Yellow) :Complement of blue (B)

The process of changing the intensity of these three colors and

mixing them to express another color is called subtractive mixing.Printers produce images in full color by this technique. Black can

be expressed by mixing C, M and Y, but development is not so

good by using just these three colors. The outcome is not black.

Therefore, black is provided separately as toner or ink. The color

system is generally called CMYK with K standing for black.

Though black begins with a B and it seems logical to say CYMB,

it might be confused with the B of blue, so K is used instead.

Most computers represent colors in 24 bits. The most recent CPUs

use 32 bits.

Why 32 bits?

Well, there are systems which represent colors in 30 and 36 bits,but because the following hardware and software restrictions, 24

bits is the mainstream.

Anything over 32 bits places a burden on the software.

When an 8-bit color is represented as 24 bits, the size allotted per

color comes to 1 byte, which is easy to process.


51/10447


The hardware cannot follow anything over 24 bits.

For example, the monitor cannot reproduce colors represented with

more than 24 bits.

Anything over 24 bits exceeds the human ability to perceive

colors.

What this implies is that using numerous gradations, even at theexpense of burdening the software and hardware, is useless

because the differences in color cannot be picked up by the human

eye.


52/10448

Chapter 4


53/10449

PDL and GDI

Technic al Infor mat ion


54/10450

1


55/10451

PDL and GDI

1 PDL and GDI

There are two basic ways to process print data. One is to convert

the data in the application software to page description language

(PDL) and then create the bitmap inside the printer and print it out.The other uses the graphics device interface (GDI) of the OS to

create print data and then have the printer bitmap it and print it out.

PDLTwo typical page description languages (PDL) are Hewlett-

Packards PCL and Adobe Systems PostScript. What PDL is all

about is that the computer must create printer language in the printdata format specified by the printer manufacturer. If the printer is

capable of translating this language, then printing can be done

without depending on the application or OS.

PCLPCL is Hewlett-Packards page description language. Its short for

Printer Control Language. It was originally conceived for dot matrixprinters and ink jet printers. It comes in various versions for use

with different types of printers.

s PCL3

PCL3 was Hewlett-Packards PDL for their first desktop laser printer.

It was very limited in terms of capabilities, enabling only a few

bitmapped fonts and small bitmapped graphics to be printed. When

Hewlett-Packard replaced their LaserJet with the LaserJet Plus, it

used the same PCL3, but made it possible to process more fonts

and larger graphics. Other printer manufacturers emulated it, but

their products lacked the precision of PCL3. Because it had the

commands and features needed to print out documents with simplelayouts and because PCL3 printers were fast and quiet, it helped

the laser printer supersede the daisy wheel printer.


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s PCL4

The LaserJet Plus was replaced by the LaserJet II series and 8

ppm* printers. The LaserJet II series included the LaserJet IIP and

4 ppm personal printers, LaserJet IID and a LaserJet II with double-

sided printing capabilities. PCL4 was used with the LaserJet II. It

was based on PCL3 but packed more bitmapped fonts and greater

capabilities for handling large bitmapped graphics. The standardLaserJet II could not process bitmapped graphics that were larger

than half a page, though full page processing was possible with

increased memory.PCL4 was downward compatible with PCL3, meaning PCL3 jobs

could be printed out with PCL4. But, more importantly, it went beyond

the word processing barrier with added functions for printing out

charts and graphics, hence making simple DTP possible. This

marked the end of PCL4s use as an office printer control language.

In personal printers, it requires less processing capacity than laterPCL versions, so it is still being used today. The PCL4 version used

with the LaserJet IIP is slightly expanded from the version used

with the standard LaserJet; it offers data compression capabilities

to reduce the data size of bitmapped graphics sent to the printer

from the computer.

* ppm stands for pages per minute and is used as a unit formeasuring printing speed.

s PCL5The LaserJet II was replaced by a LaserJet III using PCL5 command

language. The LaserJet III was an 8 ppm office printer. Other

Hewlett-Packard PCL5 printers were the IIID (8 ppm double-sided

printing), IIIP (4 ppm) and IIISi (17 ppm double-sided printing). From

its earlier versions, PCL5 has made big progress. Though it is an

escape code language, it offers many of the features of a page

description language. Perhaps, the most important new additions

to the PCL5s capabilities are outline fonts and vector graphics.

With these two features, it is possible to define practically all of the

features needed to print. Vector graphics commands were madepossible by adding language used by HPs pen-plottersa version

of HPGL (Hewlett-Packard Graphic Language)to the PCLcommand set.

Most of PCL5 is downward compatible with PCL4, but because

fonts were changed from bitmapped to outline, there are someincompatibilities. PCL5 is suited for complex document layouts, thus

it is used for DTP, graphic design and making presentations.

Outfitted with PCL5, the LaserJet III series also introduced a

smoothing technique known as Resolution Enhancement in which

a tiny dot was automatically placed on the edge of lines and

characters so as to reduce the jagged contours seen sometimes

with 300 dpi printing.

Escape code

See p. 88.


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s PCL5e

The LaserJet III series gave way to the LaserJet 4. To make the

switch, Hewlett-Packard enabled a 600 dpi print resolution, added

a high speed bidirectional parallel port (Bi-Tronics) so as to send

more printer status information to the computer, and introduced a

selection of fonts for use with applications for Microsofts Windows.

PCL5 was then expanded slightly and named PCL5e, e meaningthe expanded version. The main upgrade made it possible to convey

status messages, errors and other printer information to the

computer. The LaserJet 4 series included the LaserJet 4 (600 dpi,8 ppm), LaserJet 4L (300 dpi, 4 ppm), LaserJet 4P (600 dpi, 4 ppm)

and LaserJet 4Si (600 dpi, 16 ppm). In addition to the basic series,

a second series offered PostScript Level 2 built-in on all models as

a plus to PCL5e. Model codes of this second series were

differentiated by the addition of the letter M to the end of the code

(4M, 4ML, 4MP and 4MSi).

s PCL5c

PCL5c is one version of PCL5 and is used on HPs color ink jet

printers and color desktop laser printers. It is compatible with PCL5,

but adds commands necessary for supporting color printing.

PCL was developed by Hewlett-Packard, but it was widely copied by other

manufacturers with HP printer emulator packages labeled as LaserJet IIP

compatible or PCL5 compatible. Many of these emulators were very good and

offered added capabilities that raised them to the same functional level as the

original HP printer. They came as HP emulators and clones. Nevertheless, pages

were created in a different fashion and, consequently, visible differences could bedetected when compared against printouts from an original HP printer. A large

number of todays application developers use an HP printer to test performance of

PCL software packages. Emulators are tested with the latest major application

software, but if clone manufacturers do not adequately test their products,

printouts may not come out as expected.

About PCL Emulation


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s PostScript Level 2

With PostScript Level 1, a tremendously high processing capacity

was needed and printing was often slow. Moreover, because the

market continually saw new PostScript printers with more colors

and patterns, multiple paper trays, double-sided printing and other

functions, the language spread and things became chaotic. To

dissipate the confusion, Adobe announced their first majorexpansion. It was PostScript Level 2.

PostScript Level 2 packed all the expansions made to PostScript

Level 1 into a new package, thereby establishing a new base inPostScript language. Level 2 was loaded with major design changes

and several new features such as less restrictions on control points

and memory management. It made printing more efficient and faster.

PostScript Level 2 is completely downward compatible with Level

1, so the same images as a PostScript Level 1 printer can be created

with it.

Memory used

Memory used Usedmemory

Availablememory

Availablememory

1. Printing starts. 2. Printing starts. 3. With further printing ...

Memory is consumedbefore 1 full page ofdata is processed.

When available memoryruns out, an error is gen-erated and printing issuspended.

Level1memory

management

Memory used Memory used

Memory used

Availablememory Available memory

Availablememory

1. Printing in progress 2. With furthermemory usage

3. Available memoryis secured.

Data not used much iserased from memory.As with Level 1, mem-ory is gradually con-sumed.

Because sufficient mem-ory is available, printingcan continue uninter-rupted.

Level2memory

management


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s PostScript 3

PostScript 3 is a page description language announced in 1996. It

improved graphic drawing speed and added new capabilities such

as compatibility with CID (Character Identifier) fonts. But, the biggest

feature by far is the language expansion for Internet since the

Internet is rapidly spreading all over. The new version has been

upgraded from earlier PostScript languages with the followingcapabilities. When the application delivers the URL* to a printer

with PostScript 3, the printer itself downloads and prints the contents.

It can also directly translate and print HTML (HyperText MakeupLanguage) and PDF (Portable Document Format) files, the latter a

file format of Adobes Acrobat document exchange software.

Furthermore, paper trays can be selected from a WWW browser

and resolution can be changed.

* URL stands for Uniform Resource Locator which is an Internet

addressing scheme that defines the route to a file or a program.

CID fonts simplify the structure of old PostScript OCF (Original Composite

Format) fonts. They minimize memory consumption in the printer during printing

and speed up rasterizing.

About CID Fonts

PostScript is not used just with printers; it can be used with any type of device

that creates images by arranging dots. In fact, it has been used with many

computer monitors and imagesetters. It makes a computer monitor work at

typically maximum resolution of 100 dpi and an imagesetter at a minimum 1200

dpi. PostScript is also used in communications between documents and

computers. With PostScript, Adobe Systems also defined the standard for pagetransmission between facsimiles.

Other PostScript Devices


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Adobe Systems does not sell printers. Their revenue comes from leasing the

rights to use their PostScript language to printer manufacturers. The printermanufacturer pays a licensing fee for their PostScript printer. Because Adobe's

license is expensive, some manufacturers are trying to compete with PostScript.

These competitive products and clones differ greatly in terms of quality and

effectiveness. There are just as many bad products as there are good products.

In any case, all clones present some kind of trouble because PostScript is

extremely complicated and hard to emulate. There are no competitive products

which guarantee the exact same printout as an original Adobe PostScript printer.

If Adobe would lower their licensing fee, most clone manufacturers wouldn't try

competing with them.

About PostScript Clones

PrintGear is a printing system for low-priced printers, which Adobe has

developed. It is composed of a printer driver and a special LSI which is installed

in the printer as a processor. It also packs two printer drivers, one for each GDI

of Windows and QuickDraw of MacOS, and there is even an MS-DOS mode. The

driver converts the data created on the corresponding system, then rasterizes it

and prints it out.

About PrintGear


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GDIMicrosofts Windows, the OS used widely by IBM-AT compatiblesand PC98 series computers, has software for displaying text and

pictures on the computer screen. It can display many different typesof fonts oriented in various ways as well as bitmapped and vector

graphics. Because this Windows feature satisfies the requirements

of many computer users, software developers need not develop

the same routine for every application as long as they develop a

program which fits Windows specifications. A computer which runs

Windows requires a high speed CPU, a lot of memory and a large

hard disk. Nonetheless, these elements are vital to any high

performance printer controller. With Windows, print data is created

on the computer and sent to the printer, so the printer controller in

the printer does not require high performance computer functions.Most applications describe documents in a data format specifically

for that application. They then convert the data into bitmapped data

applicable with the connected devicemonitor or printerbeforethe data is actually sent. With Windows, bitmapped data is the same

for all applications. The system that creates it is called a Graphics

Device Interface, or GDI for short. GDI creates bitmapped data

that matches the resolution of the device (monitor, printer, facsimile,

etc.).

The GDI function that was introduced with Windows 1.0 has notbeen changed even with Windows 3.1 and Windows 95 except for

the way data is bitmapped. With Windows 2.X and earlier versions,

color bitmapping depended entirely on the hardware for the number

of colors, data saving and other matters. However, since Windows

3.0, Microsoft has adopted a device independent bitmap (DIB) and

included even a color pallet to absorb the color differences of thehardware.

With Windows 95, GDI is applicable with 32-bit systems (GDI32)

and has newly added functions to draw Bezier curves and a high

speed bitmap engine. The GDI in Windows NT has a 32-bitcoordinate system and can rotate the axes of the system.

The basic elements of GDI were perfected with the release of

Windows 95. Further drawing capability expansion centered on

multimedia was later offered under the name DirectX.DirectX

See p. 88.


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Application

GDI

Draw command

Printer driver,display driver, etc.

Computer

Printer Display Facs

2 Everything About Printer

Documents

Transcript of 2 Everything About Printer