Lecture 10. Printing Devices. Ink Jet Printers Laser Printers Thermal Printers Dye Sublimation Halftoning Dithering Error Diffusion

Transcription

1 Lecture 10 Printing Devices Ink Jet Printers Laser Printers Thermal Printers Dye Sublimation Halftoning Dithering Error Diffusion

2 Older Printing Devices Plotter Dot Matrix Printer pin motion ink covered tape ElectroMagnet paper

3 Ink Jet Printer high voltage deflection plates ink drops paper drop generator charge electrode unused ink returned to reservoir ink supply filter

4 Thermal-Bubble Ink Jet Printer (Canon,Hewlett Packard) Initial State with fluid at rest. Resistor is heated and bubble nucleates. Bubble grows to maximum ink drop is ejected. Bubble collapses. Drop breaks off. Vacuum created by bubble sucks ink from cartridge. View of the nozzles in a thermal bubble inkjet. (some nozzles per head) Demo:

5 Piezoelectric Inkjet (Epson) Piezo crystals are located at the back of the ink reservoir of each nozzle. The crystal receives a tiny electric charge that causes it to vibrate. When the crystal vibrates inward, it forces a tiny amount of ink out of the nozzle. When it vibrates out, it pulls some more ink into the reservoir to replace the ink sprayed out. Demo:

6 Laser Printer Charge Corona wire Transfer Corona wire Detach Corona wire Charge corona wire gives drum initial positive charge. Laser "draws" the image to be printed as a pattern of electrical charges -- an electrostatic image. Image is negatively charged. Positively charged toner clings to drum. Toner is deposited on paper (via Transfer wire = charged roller). Paper is discharged (via Detach wire) Toner is fused into paper with heated fuser.

7 Dot Pattern of Ink Jet and Laser Ink Printing Laser Printing Liquid ink drops are shot onto paper Solid particles are attracted to specific points on paper.

8 Color Laser Printer 4 x toner and developer mechanisms. Drum rotates x4 for a single print.

9 Dye Sublimation Printer High quality photo prints paper color plastic roll thermal elements paper thermal elements plastic ink

10 Thermal Wax Printer color wax roll paper printer head

11 Resolution Measures dots per inch and addressability Dots per inch (600) Addressable (3000)

12 Lights vs Inks Additive vs subtractive Additive Subtractive

13 Reflectance Concepts

14 Color Mixtures

15 Subtractive Color System - CMYK Printer Dyes: cyan magenta yellow black = removes red = removes green = removes blue = removes all Ideal block dyes: cyan magenta yellow transmit B G R B G R B G R

16 Cyan - controls amount of red in print: low C = high R (also high G and B) high C = low R (high G and B) cyan transmit B G R R G B High density cyan R G B Medium density cyan R G B Low density cyan Similarly Magenta - controls amount of green and Yellow controls amount of blue.

17 Multiplicative (Subtractive) Color System red = magenta + yellow B G R magenta * yellow = red B G R red green blue = magenta + yellow = cyan + yellow = magenta + cyan

18 Subtractive Colors - Summary

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23 Color Separations RGB Color Bands Original RGB

24 Color Separations CMY Color Bands Original RGB C = 1 - R M = 1 - G Y = 1 - B

25 Color Separations CMY Color Bands Original RGB C = 1 - R M = 1 - G Y = 1 - B

26 Undercolor Removal (gray component replacement) C + M + Y = K (black) Using three inks for black is expensive C+M+Y = dark brown not black Black instead of C+M+Y is crisper with more contrast. = C M Y K C M Y

27 Gray Component Removal C M Y K K(x,y) = min(c(x,y),m(x,y),y(x,y))

28 CMYK Separations With GCR

29 Spatial Effects: CMY All Blurred

30 Spatial Effects: only K Blurred

31 Ideal Block Dyes vs Printer Dyes Ideal block dyes: Actual Printer dyes: cyan B G R B G R magenta B G R B G R yellow B G R B G R

32 Problems with Printer Dyes red = magenta+yellow: B G R green = cyan+yellow: B G R blue = magenta+cyan: B G R

33 Example: Reflectance Spectra of Real Inks 1 Full density Reflectance Wavelength (nm) 1 Magenta at various densities Reflectance Wavelength (nm) HP printer

34 Tone Reproduction Curves Luminance (re: white paper) Black ink level (dv) Luminance (re: white paper) Magenta ink level (dv)

35 Printer Gamut display printer y x Colors within the Gamut can be printed.

36 Gamut Mapping How does one print this color? display printer y x This color never needed?

37 Monochrome Printing GrayScale Threshold

38 Halftoning