”A few intermediate levels can provide a substantial improvement”

INTERMEDIATE LEVELS ”A few intermediate levels can provide a substantial improvement”

Human vision -Contrast sensitivity function (CSF) ~30cycles/deg for 20/20 vision -Sensitive for disturbances with 0.5-10 mm wavelength for normal reading distance -Perceptible luminance modulation ~200 tone levels For normal reading distance

MULTILEVEL HALFTONE SCREEN Uniform quantizer

MULTILEVEL HALFTONE SCREEN Non-uniform quantizer

MULTILEVEL SCREEN OPTIMIZATION Theoretical upper limit of possible tone level combinations for a cell with Np number of pixels gmax tone levels per pixel

MULTILEVEL SCREEN OPTIMIZATION In practice, the distinguishable levels are much lower because of redundancy in tone level arrangements the difference between some levels is too small to be resolved visually

REDUNDANCY 2x2 Trilevel Halftone cells – 15 Reflectances

REDUNDANCY 2x2 Trilevel Halftone cells – 9 Unique Reflectances

REDUNDANCY Ravg = 0.25

OPTIMIZATION TRC ~ optical density out vs. optical density in Performance evaluation RMS-fit to 45° line

OPTIMIZATION Density is not linear to human visual perception Solution, a more linear measure of brightness response Munsell value L for Ravg> 0.05

OPTIMIZATION

MULTILEVEL STOCHASTIC SCREEN – USE GENERIC APPROACH TO CREATE BNM DITHER MATRIX ERROR DIFFUSION – REPLACE THRESHOLD WITH QUANTIZER AND DIFFUSE THE QUANTIZATION ERROR COLOR HALFTONING - COLOR SCREEN SUPERIMPOSITION CAN BE USED DIRECTLY. METHOD FOR ERROR DIFFUSION (OSTROMOUKHOV…)

HIGH-ADRESSABILITY

INKJET • MULTIPLE DROPLETS • MULTIPLE NOZZLES – DIFFERENT ORIFICES • MULTIPLE INKJET HEADS – DIFFERENT INKS • USE SATELLITE DROPLETS • COMBINATIONS OF 1-4

”A few intermediate levels can provide a substantial improvement”