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Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Printing.

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Presentation on theme: "Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Printing."— Presentation transcript:

1 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Printing

2 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Origin of Printing n Invented by Chinese c.1000 AD –Entire page printed at once wood cuts metal type n Reinvented in Europe, Johannes Gutenburg –Entire page printed at once movable type, could ‘reset’ the plate

3 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Traditional Printing Processes n Intaglio n Letter press / Relief n Silk screen / Porous / Stencil process n Lithography / Planographic

4 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Lithography/Planographic Process n Image and non-image areas are on the same plane. n Difference: Receptivity of ink –Image areas accept ink –Non-image areas repel ink n The plate image is the same as the print. Lithography Plate repels ink Absorbs ink for copying

5 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Intaglio Printing n The image is etched or depressed into the plate as small wells, which contain ink. n Non-image areas are the surface of the plate. n The plate image is the reverse of the final print. plate final print

6 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Letter/Relief Press n The image area is raised and inked. n The non-image area is depressed. n The plate image is the reverse of the final print. plate final print

7 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Silk Screen/Porous/Stencil Process n Image areas are porous allowing ink to pass through. n Non-image areas are non porous. n Metal, nylon, silk screen, or fibrous material is used. n The plate image is the same as the print. Screen Ink goes through Ink does not go through T-Shirt Ink

8 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Binary Printing n The traditional printing processes described maintain only two tones: color no color ink no ink image no image All printing methods from this point on, unless otherwise noted, are binary.

9 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Binary Printing n How do printers produces gray tones between the traditional ink and no-ink areas without many gray inks? n Challenge: Find a way to print continuous tone images:

10 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science n Make a grayscale … with discrete levels of gray. The Halftone Idea

11 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science The Halftone Idea n 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.

12 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science The Halftone Idea n 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

13 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science The Halftone Idea n 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.

14 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science The Halftone Idea n 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.

15 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Impact Printers n Impact Printing –A needle/head physically hits an ink ribbon onto paper leaving an impression behind. n Typewriter, 1874 –QWERTY keyboard becomes standard –Text only; No halftones –1 color ribbon n Dot Matrix Printers –Set of 9 or 24 pins form spots –Text and low quality imagery; FM halftones –1 or 4 color ribbons

16 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science The Halftone Idea Conventional/ AM/Clustered Stochastic/ FM/Dispersed n Structures of Digital Halftone Cells

17 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Spatial Resolution n dpi = dots per inch –Each dot that makes up a halftone spot –Associated with optical resolution of scanners and addressability of digital printers n lpi = lines per inch –Each spot or entire halftone cell –Usually associated with printer capabilities 1 spot of ink = 1 cell 1 inch 14 dpi2 lpi

18 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science n 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 Tone Resolution A 2x2 matrix can produce 5 tones. A 3x3 matrix can produce 10 tones. A NxN matrix can produce N tones

19 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Lots of Dots n People cannot see dots greater than 133 lpi at a reasonable reading distance. n Publications set in lpi –magazines –books

20 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Lots of Dots n People can see dots less than 133 lpi at a reasonable reading distance. n Publications set in lpi –newspapers

21 Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Summary n 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.


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