Printing Devices

Lecture 10

Ink Jet PrintersLaser PrintersThermal PrintersDye SublimationHalftoningDitheringError Diffusion

Plotter

Dot Matrix Printer

ElectroMagnet

pin motion

ink covered tape

paper

Older Printing Devices

Ink Jet Printer

paper

unused inkreturned to

reservoir

filterink supply

drop generator

chargeelectrode

high voltagedeflection plates

ink drops

View of the nozzles in athermal bubble inkjet.

(some 300-600 nozzles per head)

Thermal-Bubble Ink Jet Printer

Initial Statewith fluid at

rest.

Resistor is heated and

bubblenucleates.

Bubble growsto maximum

ink drop is ejected.

Bubble collapses.

Drop breaks off.

Vacuum createdby bubble sucks

ink fromcartridge.

(Canon,Hewlett Packard)

Demo: http://www.howstuffworks.com/inkjet-printer3.htm

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: http://www.howstuffworks.com/inkjet-printer3.htm

DetachCorona

wire

Laser Printer

ChargeCorona

wire

TransferCorona

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.

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.

Color Laser Printer

4 x toner and developer mechanisms.Drum rotates x4 for a single print.

Dye Sublimation Printer

color plastic roll

paper

thermal elements

paper

plastic inkthermal elements

High quality photo prints

Thermal Wax Printer

paper

color wax roll

printer head

Resolution Measuresdots per inch and addressability

Dots per inch (600)

Addressable (3000)

Additive Subtractive

Lights vs Inks Additive vs subtractive

Reflectance Concepts

Color Mixtures

Subtractive Color System - CMYK

cyan

magenta

yellow

black

= removes red

= removes green

= removes blue

= removes all

Printer Dyes:

cyan magenta yellow

B G R B G R B G R

trans

mit

Ideal block dyes:

Cyan - controls amount of red in print:

low C = high R (also high G and B)high C = low R (high G and B)

R G BR G BR G BHigh density

cyanMedium density

cyanLow density

cyan

cyan

B G R

trans

mit

Similarly Magenta - controls amount of greenand Yellow – controls amount of blue.

yellow

Multiplicative (Subtractive) Color Systemred = magenta + yellow

magenta

B G R

red

*

=

B G R

= magenta + yellow= cyan + yellow= magenta + cyan

redgreenblue

Subtractive Colors - Summary

Color Separations

OriginalRGB

RGB Color Bands

Color Separations

OriginalRGB

C = 1 - RM = 1 - GY = 1 - B

CMY Color Bands

Color Separations

OriginalRGB

C = 1 - RM = 1 - GY = 1 - B

CMY Color Bands

Undercolor Removal

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.

100 50 70

(gray component replacement)

=

50 0 2050

+

C M Y C M YK

Gray Component Removal

K(x,y) = min(C(x,y),M(x,y),Y(x,y))

C M Y

K

CMYK Separations With GCR

Spatial Effects: CMY All Blurred

Spatial Effects: only K Blurred

cyan

magenta

yellow

B G R

B G R

B G R

Ideal block dyes:

Ideal Block Dyes vs Printer Dyes

B G R

B G R

B G R

Actual Printer dyes:

Problems with Printer Dyes

red = magenta+yellow:

green = cyan+yellow:

blue = magenta+cyan:

B G R

B G R

B G R

Example:Reflectance Spectra of Real Inks

HP printer

Full density

Wavelength (nm)400 500 600 700

Ref

lect

ance

0.1

0.3

1

Magenta at various densities

Wavelength (nm)500 600 700

1

0.1

0.3

400

Ref

lect

ance

Tone Reproduction Curves

Black ink level (dv)

Lum

inan

ce (r

e: w

hite

pap

er)

Magenta ink level (dv)

Lum

inan

ce (r

e: w

hite

pap

er)

0 0.2 0.4 0.6 0.80

0.2

0.4

0.6

0.8

x

y

printerdisplay

Printer Gamut

Colors within the Gamut can be printed.

Gamut Mapping

0 0.2 0.4 0.6 0.80

0.2

0.4

0.6

0.8

x

y

printerdisplay

How does one print this color?

This color never needed?

Monochrome Printing

GrayScale

Threshold

Halftoning