TYPES OF DIGITAL GRAPHICS

  1. Computer art
  2. Synthetic art
  3. Mechanical art
  4. CAD-computer assisted design or drafting is used in technical drawing or illustration
  5. Pixel-picture element
  6. Bit maps-real-world analog to a mosaic made from tiny colored tiles

Dithering, or mixing tiles of the available color of shades of gray achieves the illusion of nonexistent colors or grays.  Pixels let you achieve artistic effects that resemble traditional painting with electronic edit ability.  Photo retouching programs work with bitmaps.

Object-oriented art

Vector oriented graphics are produced by drawing programs and overcome the limitations of bit maps.  Images are composed of mathematically described objects and paths, called vectors.  Color reproduction is broken down into red, green, and blue, which are called additive primaries because three lights of these colors when added together produce white light.  Color separation includes Cyan, magenta, and yellow, which are called subtractive primaries because each represents two additive primaries left under one primary has been subtracted from white light.  Operation of reducing colors and printing a full black in shadow areas is called undercolor removal (UCR).

Color corrections compensate for the spectral errors in inks and exposure errors in photography that are done manually by dot etching, photographically by masking and electronically by scanning.  Dot etching refers to corrections made to increase or reduce floor in local areas of halftone negatives or positives.  Masking is when color corrections are made photographically, which can include both positive and negative masking.  There also exists direct screening and electronic scanning.  Electronic scanning is the system of choice for color separation and correction. Screen angles and Moiré, a secondary and visually evident superimposed pattern created, for example, when two identical patterns on a flat or curved surface are overlaid while displaced or rotated a small amount from one another are commonly used.

Color proofing-purpose is to see if all the elements fit and are in the right color, and how the job will look when it is printed.  Two types exist press and off-press.  Off-press proofs: overlay, integral and digital.

Retouching, Opaquing, and Registering

There are 3 basic types of arrangement of pages for printing: sheetwise, work-and-turn, and work-and-tumble.  Books and magazines are printed in units of a number of papers per sheet called signatures.

Digital Image Processing

Color Electronic Pre-press Systems (CEPS), which integrate all the prepress operations of color separation, correction, retouching and other image modifications, page makeup and imposition.  Desktop Publishing is a concept that covers the creation and production of typographic pages with desktop devices.

Word Processing programs allow the input, editing, formatting, and printout of pages of text.  Spreadsheet programs allow columns and rows of numbers and other data to be organized, formulated and mathematically constructed.  Database programs allow the storage of records (individual items) with fields of data to permit sorting and reorganization for list and file management.  Type manipulation programs distort and manipulate type to create special effects, graphic elements, and logos.  Page layout programs assemble type, graphics, and pictures into page form for typographic printout.

Synthetic art programs allow the creation of art and illustration with sophisticated drawing tools.  Imposition programs take page files and position them on film exposed by large sheet imagesetters to produce imposed plate-ready flats. Color retouching software programs can make changes in color images scanned into the system, integrating other images and modifying color.

Electronic Editing

Scrolling is used to move the memory data up and down to bring the required section onto the screen.  Functions that are performed on the screen within moments of the operator’s request are called foreground functions.  Functions that must take place off-screen are called background functions.  Electronic editing is always a foreground approach.  To see the files that are stored on the system’s magnetic memory the operator requests a screen directory.

Page Description Language

A page description language consists of three parts: the interpreter, which converts the driver data from the front end into the coding of the printout device; the raster image processor (RIP) which organizes font data and creates the page bit map; and the marking engine which actually produces an output image.

PostScript

Adobe Systems introduced Postscript as a language developed for producing typographic pages.

Hard Copy Considerations

Line and Edge definition refers to the sharpness and clarity of character and graphic outlines.  Sometimes called an edge gradient.  Dimensional accuracy is affected by the tracking (movement) of the imaging material, the imaging system and the printer resolution.  Area filling is necessary for bars, pies, shading between lines and for character fill.  Color gamut and fidelity refers to the range of colors attainable by a printer.  Image resolution is defined as the number of “discernible line pairs per inch.”  Speed or copy time issues are how long it takes to get the first and subsequent copies of the same page.Offload speed-the computer tied up during the entire printing process?  What’s your processing speed or how fast is raster image processing?

Printers

Printer Resolution is the measurement of printer quality is known as resolution.  It is expressed as spots per inch (spi) or dots per inch (dpi).  DPI is more common, but it conflicts with the term dot as used in halftone dot, which is entirely different.  The Print speed is the most often advertised attribute and it tells how fast the device can produce output after processing is complete.  Cost per copy-price per page, is variable and should include the cost of all consumables.  Duty Cycle-number of copies that can be produced in a given time without adversely affecting the device or the copy quality.

  1. Output Printers-they have three basic functions: 1) final copy for reproduction–the output will be used to produce a plate for printing 2)Proofing-the output will be used for review and approval 3)Demand printing-the output will be used as the final end product for users.
  2. Dot matrix printers-companions to personal computers.
  3. Thermal-wax transfers printers-offer 300 spi printing with either three or four pass inked ribbon transfer rolls.
  4. Thermal dye sublimation transfers printers-require precise control of the thermal head temperature by the electronic circuits.
  5. Thermal dye diffusion transfer (D2T2) printers-use a thermal printhead and ribbon similar to thermal-wax transfer printers.
  6. Ink-jet printers-produce images by using liquid inks (mostly water-based) which are ejected from a printhead either by a pumping action by a piezo electric crystal (drop on demand), or by vapor pressure from a vaporized droplet of ink (thermal ink-jet or bubble-jet
  7. Laser printers-that produce black-and-white images on plain paper have replaced or picked up much of the text workload from line printers and daisy wheel printers and the graphics from pen plotters, dot matrix printers and some photo-plotting film recorders.  Typesetter versus imagesetter-imagesetter can output graphics and pictures in addition to type.  Drum-based imagesetters-prefferred for color reproduction because they produce more accuracy and repeatability of images for each of the four films than would be output from an imagesetter.
  8. Platesetters
  9. Press
  10. Electronic printers

Graphic Formats

Graphic data is stored in a variety of ways of storing images, called formats, for integration in other application programs.  Three of the most common are:

1) Tagged Image File Format (Tiff): the most flexible and reliable method for storing bit-mapped images in various resolutions, gray levels and colors.  It cannot store object-oriented images.  TIFF was created specifically for storing gray scale data, and is a standard format for scanned photographs.  Although TIFF is considered a standard graphics format, some programs save TIFF images with subtle variations, which may prevent the files from being handled by other application programs.

2) Encapsulated PostScript (EPS): popular format for storing vector or object-oriented artwork.  It can also store bit maps.  An EPS file in ASC11 format usually contains two versions of the graphic.  The main image is a resolution-independent PostScript description for printing on a PostScript device.  The second, optional image is a low-resolution, bit-mapped preview that can be displayed on-screen.  This double-image scheme enables page-layout programs to import, crop and scale high-quality EPS graphics while using the screen version for the user.  EPS files can be resized, distorted or cropped and most programs that perform color separations accept and color separate them.  At present, they cannot be re-edited.

3)Pure PostScript File: A purely text-based description of an image, without the displayable screen image that EPS offers.  In many applications, you can create a PostScript file and then open the file with any word processor and modify typographic and positioning information (if you know Postscript coding).  You do not need the originating program t print the file.  The PostScript file can be sent to a PostScript printer with a download utility.  There is no preview image, and the graphic essentially loses all editability.  Scanners consist of Desktop scanner and high-end scanners.

Color Publishing Systems are the integration of one or more workstations, linked on a network with data storage, scanner and print out alternatives (with appropriate applications software) results in a system that can be used to create and/or produce color images for printing or presentation.  Called CEPS.

The 5 levels include Designer/Creative Level Systems, Desktop Prepress Level Systems, Mid-Level Production Systems,

Workstations and Prepress Application Software

 

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