printing devices - haifacs.haifa.ac.il/hagit/courses/ist/lectures/ist10_printers.pdf · printing...
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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
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