Lecture 10 Printing Devices Ink Jet Printers Laser Printers Thermal Printers Dye Sublimation Halftoning Dithering Error Diffusion
Older Printing Devices Plotter Dot Matrix Printer pin motion ink covered tape ElectroMagnet paper
Ink Jet Printer high voltage deflection plates ink drops paper drop generator charge electrode unused ink returned to reservoir ink supply filter
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 300-600 nozzles per head) 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
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.
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 High quality photo prints paper color plastic roll thermal elements paper thermal elements plastic ink
Thermal Wax Printer color wax roll paper printer head
Resolution Measures dots per inch and addressability Dots per inch (600) Addressable (3000)
Lights vs Inks Additive vs subtractive Additive Subtractive
Reflectance Concepts
Color Mixtures
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
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.
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
Subtractive Colors - Summary
Color Separations RGB Color Bands Original RGB
Color Separations CMY Color Bands Original RGB C = 1 - R M = 1 - G Y = 1 - B
Color Separations CMY Color Bands Original RGB C = 1 - R M = 1 - G Y = 1 - B
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. = + 100 50 70 50 50 0 20 C M Y K C M Y
Gray Component Removal C M Y K K(x,y) = min(c(x,y),m(x,y),y(x,y))
CMYK Separations With GCR
Spatial Effects: CMY All Blurred
Spatial Effects: only K Blurred
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
Problems with Printer Dyes red = magenta+yellow: B G R green = cyan+yellow: B G R blue = magenta+cyan: B G R
Example: Reflectance Spectra of Real Inks 1 Full density Reflectance 0.3 0.1 400 500 600 700 Wavelength (nm) 1 Magenta at various densities Reflectance 0.3 0.1 400 500 600 700 Wavelength (nm) HP printer
Tone Reproduction Curves Luminance (re: white paper) Black ink level (dv) Luminance (re: white paper) Magenta ink level (dv)
Printer Gamut 0.8 0.6 display printer y 0.4 0.2 0 0 0.2 0.4 0.6 0.8 x Colors within the Gamut can be printed.
Gamut Mapping How does one print this color? 0.8 0.6 display printer y 0.4 0.2 0 0 0.2 0.4 0.6 0.8 x This color never needed?
Monochrome Printing GrayScale Threshold
Halftoning