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”A few intermediate levels can provide a substantial improvement”

This article explores how a few intermediate levels in multilevel halftone screens can significantly enhance human vision. It discusses the contrast sensitivity function of human vision and the perceptible luminance modulation for normal reading distance. The article also examines the theoretical upper limit of possible tone level combinations for a cell, as well as the impact of redundancy in tone level arrangements. Additionally, it addresses the use of optimization techniques and the evaluation of performance. The article concludes by discussing the application of color superimposition and error diffusion in color halftoning methods, as well as high-adressability inkjet technology.

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”A few intermediate levels can provide a substantial improvement”

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

  2. 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

  3. MULTILEVEL HALFTONE SCREEN Uniform quantizer

  4. MULTILEVEL HALFTONE SCREEN Non-uniform quantizer

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

  6. 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

  7. REDUNDANCY 2x2 Trilevel Halftone cells – 15 Reflectances

  8. REDUNDANCY 2x2 Trilevel Halftone cells – 9 Unique Reflectances

  9. REDUNDANCY Ravg = 0.25

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

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

  12. OPTIMIZATION

  13. OPTIMIZATION

  14. 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…)

  15. HIGH-ADRESSABILITY

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

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