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Printing. Origin of Printing. Invented by Chinese c.1000 AD Entire page printed at once wood cuts metal type Reinvented in Europe, Johannes Gutenburg Entire page printed at once movable type, could ‘reset’ the plate. Traditional Printing Processes. Intaglio Letter press / Relief

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printing

Printing

Chester F. Carlson Center for Imaging Science

origin of printing
Origin of Printing
  • Invented by Chinese c.1000 AD
    • Entire page printed at once
      • wood cuts
      • metal type
  • Reinvented in Europe, Johannes Gutenburg
    • Entire page printed at once
      • movable type, could ‘reset’ the plate

Chester F. Carlson Center for Imaging Science

traditional printing processes
Traditional Printing Processes
  • Intaglio
  • Letter press / Relief
  • Silk screen / Porous / Stencil process
  • Lithography / Planographic

Chester F. Carlson Center for Imaging Science

lithography planographic process
Lithography/Planographic Process
  • Image and non-image areas are on the same plane.
  • Difference: Receptivity of ink
    • Image areas accept ink
    • Non-image areas repel ink
  • The plate image is the same as the print.

Plate repels ink

Lithography

Absorbs ink for

copying

Chester F. Carlson Center for Imaging Science

intaglio printing
Intaglio Printing
  • The image is etched or depressed into the plate as small wells, which contain ink.
  • Non-image areas are the surface of the plate.
  • The plate image is the reverse of the final print.

plate

final print

Chester F. Carlson Center for Imaging Science

letter relief press
Letter/Relief Press
  • The image area is raised and inked.
  • The non-image area is depressed.
  • The plate image is the reverse of the final print.

plate

final print

Chester F. Carlson Center for Imaging Science

silk screen porous stencil process
Silk Screen/Porous/Stencil Process

T-Shirt

  • Image areas are porous allowing ink to pass through.
  • Non-image areas are non porous.
  • Metal, nylon, silk screen, or fibrous material is used.
  • The plate image is the same as the print.

Ink

Screen

Ink goes

through

Screen

Ink does not go through

Chester F. Carlson Center for Imaging Science

binary printing

color no color

ink no ink

image no image

Binary Printing
  • The traditional printing processes described maintain only two tones:

All printing methods from this point on,

unless otherwise noted, are binary.

Chester F. Carlson Center for Imaging Science

binary printing1
Binary Printing
  • How do printers produces gray tones between the traditional ink and no-ink areas without many gray inks?
  • Challenge:

Find a way to print continuous tone images:

Chester F. Carlson Center for Imaging Science

the halftone idea
The Halftone Idea
  • Make a grayscale …

with discrete levels of gray.

Chester F. Carlson Center for Imaging Science

the halftone idea1
The Halftone Idea
  • Early artists used the Halftone Idea and alternatives to make gray with dots or lines:
    • Stippling, lithography, mezzotint, etc.

A work by Albrecht Dürer employs both lines and dots.

Chester F. Carlson Center for Imaging Science

the halftone idea2
The Halftone Idea
  • Levels of Gray
    • Decrease the amount of black concentrated in an area to make it look lighter:
      • spaced lines and dots
    • Increase the area covered in black to darken it:
      • condensed lines and dots

Chester F. Carlson Center for Imaging Science

the halftone idea3
The Halftone Idea
  • The spacing and size of markings used to simulate gray depend on:
    • Human Visual System:
      • Don’t want people to distinguish lines / spots
      • Roughly, people see up to 60 lines per inch (lpi) at 2 ft.
    • Viewing Distance

Zoom farther out and the dots appear smaller.

Chester F. Carlson Center for Imaging Science

the halftone idea4
The Halftone Idea
  • Two Types of Halftone Spots:
    • AM: Amplitude (or Area) Modulated spots have a fixed screen ruling and vary in size
    • FM: Frequency Modulated spots have a fixed size and vary in line spacing.

Chester F. Carlson Center for Imaging Science

impact printers
Impact Printing

A needle/head physically hits an ink ribbon onto paper leaving an impression behind.

Typewriter, 1874

QWERTY keyboard becomes standard

Text only; No halftones

1 color ribbon

Dot Matrix Printers

Set of 9 or 24 pins form spots

Text and low quality imagery; FM halftones

1 or 4 color ribbons

Thwack

Impact Printers

Chester F. Carlson Center for Imaging Science

the halftone idea5
The Halftone Idea
  • Structures of Digital Halftone Cells

Conventional/

AM/Clustered

Stochastic/ FM/Dispersed

Chester F. Carlson Center for Imaging Science

spatial resolution
dpi = dots per inch

Each dot that makes up a halftone spot

Associated with optical resolution of scanners and addressability of digital printers

lpi = lines per inch

Each spot or entire halftone cell

Usually associated with printer capabilities

1 inch

1 spot of ink = 1 cell

Spatial Resolution

14 dpi

2 lpi

Chester F. Carlson Center for Imaging Science

tone resolution
Tone Resolution
  • Digital Halftone Cells
    • Based on a grid of spots (halftone cell):
    • Change the number of dots in a spot to make different tones of gray
  • A 2x2 matrix can produce 5 tones.
  • A 3x3 matrix can produce 10 tones.
  • A NxN matrix can produce N2 + 1 tones

Chester F. Carlson Center for Imaging Science

lots of dots
Lots of Dots
  • People cannot see dots greater than 133 lpi at a reasonable reading distance.
  • Publications set in 133-150 lpi
    • magazines
    • books

Chester F. Carlson Center for Imaging Science

lots of dots1
Lots of Dots
  • People can see dots less than 133 lpi at a reasonable reading distance.
  • Publications set in 65-100 lpi
    • newspapers

Chester F. Carlson Center for Imaging Science

summary
Summary
  • The Halftone Idea
    • The creation of gray levels utilizing dot formations of color on a white background.
    • Dot size and spacing are varied to create different levels of gray.

Chester F. Carlson Center for Imaging Science

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