Welcome Koen Van de Poel Chairman Origination&Prepress WG @ CIP4 Technology Staff @ AGFA Prepress.
Principles of Prepress
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Transcript of Principles of Prepress
© 2004 Print Media Academy • Wolfgang Wallowy • Principles of Prepress.ppt
Offset Printing Technology
Principles of Prepress
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Contents:
• The way to the digital workflow• The production steps• History• Reproduction – What’s that?• The original copy: Text, graphic, picture• Digital data • Fundamentals of color theory• From the original to the printing plate• The Screen• Postscript, PDF, PPF, JDF, CIP...• The workflow• Color management• Standardization• Output and process automation• Prinect MetaDimension• Proofing and PDF workflow• Imposition – digital full pages• Computer-to-Plate equipment technology
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The production process of printed products
Prepress Press Postpress
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Possible workflows in prepressImages are scanned, electronically processedand positioned, then separated and screened
RIPFilm processing
Film proofing
Film checking
Plate making
Plate development
PrintingComplete processingof A3 signatures
Digital proofing
RIPPlates are directlyimaged in thepress and printed
Complete processingof signatures
Digital proofing
RIP
Hard and soft proofing
Plate exposureand development
Printing
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A prepress workflow in general
Plate ( Film) imaging
CIP4 ProcessingScan & image processing( Scanner or Digital Camera)
Layout, text & graphic workstation
Single pages proof stationcolor- & text correction
Server( Data Manager)
Digital sheet assembly( imposition scheme)
Form proof(proof of complete print form)
Data exchangewith press and finishing
External Data
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The way to the digital workflow
Prinect Prepress Interface
FoldingCutting
PC
PrinectPrintready System
Database
PrinectSigna Station
Internet Portal
PrinectPrinance
PrinectData Control
Stitching
PrinectPrint Center
PrinectCP2000 Center
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Distributed tasks in the past
Repro house
Compositor
Assembly
Printing houseAgency
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Reproduction – What was is that?
The photographic masks, called repro films or lithos, were “photographed“ mainly with large-size repro cameras:
- Color separations were exposed with RGB color filters and corresponding correction masks on special sensitive films
- Screens were produced with engraved glass screens or contact screens- The finished lithos were then – depending on the printing method – assembled
one over the other and true to register on transparent polyester foil
Klimsch Repro devices of the19seventies
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What is an original copy?
The original copy comprises the following elements:
- Picture- Text/type- Graphic
These elements are created by means of scanners, digital cameras, application software
Picture
Scanner,digital
camera
ABCText
Computer, software,
fonts
Graphic
Computerand
software
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Fundamentals of color theory
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Fundamentals of color theoryWhat happens in the head ?
• The color receptors of the human eye react to colors• Cone-shaped receptors = color• We recognize the three main fields red – green – blue• Rod-shaped receptors = black, white, gray
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How the human eye perceives light
Whitelight
Lightsource
Prism
Prismatic colors
Color receptors of the eye
• A prism splits sunlight or white artificial light into prismatic (rainbow) colors of the electromagnetic spectrum
• So WHITE is the sum of all colors; BLACK, i.e. no light, means no color• The so-called color receptors of the eye (red, green and blue) receive these pieces
of the picture, the brain then combines all this information in one “color“ picture
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Additive color mixing
• Red, green and blue are the base colors of additive color mixing (TV, monitor, beamer, video)
• If a white area is illuminated with three spot lights in red, green and blue, the eye perceives a white spot where the three light bundles overlap
• The addition of two base colors generates lighter complementory colors
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Subtractive color mixing
• The base colors in subtractive color mixing are cyan, magenta and yellow.
• Overprinting, they add up to black• The white paper serves as the reflector• The more color is applied to the paper,
the more light is reduced• Color absorbs its own complementary
color and reflects its own inherent color• Autotypical color synthesis
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From the original to the printing plate
The way from the original to the printing form/printing plate:• Creation of the document• Page layout, text, graphic• Scanning of pictures• Integration of all elements• Imposition, if required• Transformation of the computer data
into an imageable bitmap• Exposure of the film or the
printing plate (on-press or off-press)
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Scanning
• By scanning strip by strip and step by step as well as through the color separation with the RGB filters, 3 bitmaps are generated for red, green and blue
• With an appropriate software, RGB are converted into cyan, magenta and yellow taking into account the necessary corrections
• Black is generated by using a special color filter or by calculating it as the fourth bitmap
• The precision of many scanners allows to reconvert screened films into bitmaps (copix)
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Data input is complete and ready for output
• All elements, i.e. picture, type (text) and graphic, are combined into one unit, i.e. one or more pages, one document, on a workstation
- The documents are now ready for a digital specimen print, for imposition or for exposure on film or printing plate or direct imaging to press
Type
TypeABC
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How the digital code works
AaBb12
ASCII-Code
010000010110000101000010011000100011000100110010
MorseSignals
· -
- · · ·
· - - - -· · - - -
• Computers use the binary code, i.e. the representation of information with the figures 0 and 1 = 1 bit (binary digit)
• A group of 8 bits forms one byte, i.e., one of 256 definition or switch possibilities:1 bit = 2 switch conditions 0 or 1,2 bits = 4 switch conditions8 bits = 256 switch conditions = 1 byte
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The Bitmap
0 0 0 0 0 1 1 1 0 0 0 0 00 0 0 0 0 1 1 1 0 0 0 0 00 0 0 0 1 1 1 1 1 0 0 0 00 0 0 0 1 1 1 1 1 0 0 0 00 0 0 0 1 1 0 1 1 0 0 0 00 0 0 1 1 1 0 1 1 1 0 0 00 0 0 1 1 0 0 0 1 1 0 0 00 0 1 1 1 0 0 0 1 1 1 0 00 0 1 1 1 0 0 0 1 1 1 0 00 0 1 1 1 1 1 1 1 1 1 0 00 1 1 1 1 1 1 1 1 1 1 1 00 1 1 1 0 0 0 0 0 1 1 1 00 1 1 0 0 0 0 0 0 0 1 1 01 1 1 0 0 0 0 0 0 0 1 1 1
• The digital, geometric representation in a kind of chessboard pattern is used with image data (scanners, digital cameras) and for controlling printers and exposure units
• This format of digital representation is also called bitmap. It is a map consisting of bit (or byte) data, i.e. of pixels or picture elements
• The fineness or resolution is expressed in dots per inch (dpi)
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The Vector Format
TypeType
• Besides the bitmap format for pictures, there is the so-called vector format for line art and text in which all elements are defined by geometric formulas, e.g. Bezier curves
• These vector data are not converted into the known bitmaps until the output on a printer or exposure unit
• The advantage of vector data is that they are independent of size and resolution, e.g. withtypefaces, smaller quantity of data
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The Screen
• Why is a screen used?• With all known printing methods of letterpress and
offset – gravure printing is an exception. In order to create visual tonal gradations the screening technique is used
• Gray values are represented by dots of different diameters, mostly in a regular arrangement (therefore: screen)
• The human eye mixes the different reflection intensities thus created into one gray tone or graded halftone
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The Screen Angle
• When 2 screened images are printed on top of each other and their screen angles are not in perfect register, a moiré pattern may occur
• The screen angle relationship of 30° is common
• Since 3x30° means 90°, a 4th color would lie on one of the already existing angles
• Yellow distinguishes only little from the paper white and the other colors, therefore a special trick is used, i. e. yellow is positioned at an angle of 15° in relation to 2 colors, mostly on 90°
Standard angle positions
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Screen Ruling
Schematic representation of a screen of an approx. 30% tone value and at an angle of 105°
• The distance between the dots is called screen ruling
• There is a rule: A coarse screen for bad paper grades (coarse surface) like newsprint paper, a fine screen for coated paper grades (art paper)
• For art paper, normally screen rulings of 60-70 l/cm are used, with the modern print quality, it is no problem to print much higher screen rulings
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Screen Construction
• With an imaging resolution of 100 l/cm, there is a basic area of 16 x 16 spots for every dot between 0% -100%
• Thus it is possible to represent 256 tone values per dot, enough for the human eye
• Under these conditions, an output devicerequires a total of 0.921 mio. commands in order to switch the laser beam on or off for all spots on an area of 1 cm2
Halftone valueapprox. 82%
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The Raster Image Processor (so-called "RIP")
Layout/Document
Type
Type
• The production of the bitmap to be printed and the allocation of the screens for halftone pictures / sets of color separations takes place in the so-called RIP process with the original CMYK image data and the original typefaces being used
• It is based on the PostScript page description language (Adobe) and a suitable software on a standard computer platform (Software-RIP, e.g. Prinect MetaDimension)
• In printers, the RIP is in the device itself (Hardware-RIP)
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What is behind the terms PostScript , PDF, PPF, JDF, CIP ...?
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What is PostScript?
PostScript is a page description language fromPS achieved its breakthrough with the launch of the first RIP (raster image processor) by Linotype in 1985 for the Linotronic 300 from Linotype-Hell AG
Important PostScript components are e.g.the programming language,the printer driver, andan interpreter (RIP) as well as Type 1-fonts
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What happens in the PostScript-RIP?
• Application-specific modifications are realized, e.g. distorting, image enlargements, gradation adjustments, etc.
• Graphic elements (pictures, graphics) are converted into screens, including screen angles, screen ruling, dot shape and calibration (e.g. print characteristic curve)
• For every color, a separate bitmap is generated in black and white
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closepath} def
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Endegrestoreshowpage
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What is PDF (Portable Document Format)?
• PDF is a page-oriented PostScript data format which can easily be produced (PDF-writer/printer driver), in which superfluous command and definition structures are eliminated (lean PS) and which can be represented and – to a limited extent –edited with simple tools (Adobe Acrobat Reader, Freeware) across different platforms
• It even simulates missing fonts with an approximate character width and approximate font characteristics
Wor
kflo
w
PDF view
Prep
ress
PDFprinterdriver
PDF fileDocument
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Prinect Prepress Interface
Digital Imposition RIP Printing PlatesComputer-to-Plate
Or via online connection
Job Memory Card
Ink Zone Profiles
Print ProductionFormat PPF
PrepressInterface
CIP4
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From Print Production Format towards Job Definition Format
Introduction DRUPA 1995
Horizontal Integration of Production Workflow
• PPF-Format (Print-Production-Format):A PPF-file can contain the following data:
- Job and commercial data- Low-res bitmaps of the printed sheets- Transfer curves- Register marks- Color and density measuring points- Cutting, folding and stitching folding data
Introduction DRUPA 2000
Vertical and horizontal Integration ofProduction and Business Workflow
• The PPF-format can be used for: - Automatic ink zone setting- Make ready of cutter, folding and
stitching machines
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• The automation of the production processes in the printing industry has made great progress over the last few years
• Within the classic production units prepress, press and finishing, production can be highly automated, on the condition that it is an environment from just one manufacturer
• Standardized data formats as CIP 4 bridge the borders between Prepress, Press and finishing and production data capturing
Scanner Film-/ Platesetter
Printing Press Cutting-/ Folding Machine
Workstation
JDF Actual Data
JDF Planned Data
3rd PartyMachines
and Software
What is JDF (Job Definition Format)?
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... and to make sure it really works, a standardized color work flow from input through to printing
Color Management is a precondition and a tool for matching all components involved in a workflow with a preset standard
The Digital Proof- Simulates the print run on the printing press- Is a preview of the printing result- Requires appropriate resolutions and repeat accuracy
Standardization
Calibration
Profiling
Applications
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Why Color Management ?
Press
Scanner
Proofer
Monitor
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Color Management
• Graphical representation of color spaces described by ICC profiles
• Color spaces have different shapes and dimensions.
• Every device has its own speciallydefined color space
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Targets of Print Color Management
ICC-Profile Proofs and standardized print
Optimizing of Printing press
Optimizingof PrePress
Standardization
Process control
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We must have a common order!
With the device-independentCIELAB color space
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-b
+b
+a-a
-b
+b
+a-a
Commission Internationale d’Éclairage (CIE)- Specification of the Lab color space 1976- Device-independent,- Based on human color perception
International Color Consortium (ICC)- Specification of the ICC profile format 1994- Computer-independent,- Manufacturer-independent
Color Management is based mainly on international standardization
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With precise color space descriptions
In the form of ICC profiles
Classified for scanners, monitors andprinters / proofers / printing presses
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Color Management !
Press
Scanner
Proofer
Monitor
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High-performance PDF and PS 3-RIP
Open PDF workflow- Combinations with Prinect SignaStation, Prinect Printready System,
Prinect MetaDimension and Prinect MetaShooter, etc. are available according to requirements
- Open for any “self-made PDF workflows” with Acrobat plug-ins and applications
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Preflow: Generation of a perfect PDF!
• JobStream generates a clean PostSriptpreflight PDF after the distiller
- Pitstop for PDF-editing and preflight check
- Pitstop Server for automatic preflight of large quantities of documents and revisions of the PDFs
• Interactive trapping of PDF with Supertrap• Optimized PDFs for Prinect MetaDimension
for imposition, form and color proofing, output on film or plate
• State of the Art PDF trapping• Very fast and easily operated Acrobat plug-in
- Interactive and automatic- Standard and user-defined parameters- Efficient spreading of special colors- Image-to-image spreadings
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What’s imposition, please?
The term imposition describes the arrangement of pages on a print sheet taking into account the finishing steps in finishing:
- like folding,- collecting,- and binding technologies like adhesive
binding, saddle stitching/thread stitching
The arrangement of the pages is always defined by the sequence of pages and the dimensions of the individual pages
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2 15 14 37 10 11 6
• The folding schemedetermines thearrangement of thepages
• The pages are brought into the desired sequence by folding
• After trimming at three sides, the „copy book“ can be opened
The print sheet
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Advantages and disadvantages of digital printing plate production
• Very short production times• Very high quality of the printing plates• Maximum register-trueness• Less make-ready times in printing• Less waste
• All elements need to be available in a digital form, e.g.
- print control strip- process control strip- cutting – folding marks
• Redigitization of old data is necessary • Digital proof systems are required
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Equipment technology
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Imaging techniques and design features
Internal drum imagesetterExternal drum imagesetter
Modern imagesetter technologies comprise the following 3 categories – listed by production expenses:
- Capstan imagesetters work via a polygon onto material on a roll which is transported in a synchronized way with the rotation,
- Internal drum imagesetters expose onto fixed material (sheets cut from a roll),
- External drum imagesetters direct the laser beam strip by strip onto a rotating drum holding the material to be exposed.
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The Capstan Principle
• Costly synchronization of optical system• Adjustment of light intensity between the
center and the edges of the material (beam length differences)
• Suited for film and polyester plate• Comparatively low production costs• Link to online processor
Laser source
Polygon
Film material
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The Internal Drum Principle
• Costly production of the internal drum, fixed film, high repeat accuracy
• Identical beam length in all positions• Simple optical system (prism)• Only 1 laser beam for imagesetting, from roll to
sheet, roll to roll• Link to online processor,• Integrated register • Punching system for film
and polyester plate
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Offset Printing Technology
Principles of Prepress
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