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Fundamentals

Fundamentals. Motivation. Issue Text and lines are indispensable to print quality Toner overdevelopment causes toner scatter Toner scatter makes printed pages appear blurred near the edges of text or thin lines Current solutions Limit the color gamut of printers

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Fundamentals

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  1. Fundamentals

  2. Motivation • Issue • Text and lines are indispensable to print quality • Toner overdevelopment causes toner scatter • Toner scatter makes printed pages appear blurred near the edges of text or thin lines • Current solutions • Limit the color gamut of printers • Undesired color shifts and introduction of halftone texture • Compensate for toner overdevelopment by the coring algorithm • Little research due to new exclusive method

  3. Toner Scatter EP process Effect of toner scatter

  4. Overview of Coring • Technique of decreasing amount of colorant in the interior of text or characters to diminish effect of toner scatter • Optimal coring value: minimum decrease of colorant amount by percentage ∆ of nominal colorant level No coring 18% coring 50% coring Profile of cored line Annulus with10-pixel width Printed at 600 dpi, scanned at 1200 dpi

  5. Overview of Coring (cont.) • By utilizing both high and low resolution image data Coring algorithm

  6. Goals • Reduce toner scatter in region of interest, while yielding the appearance of sharper edge transition • Overcome disadvantages caused by limiting the color gamut of printers No coring Optimally cored color clipped Printed at 600 dpi, scanned at 1200 dpi

  7. Outline • Remote Print Defect Diagnosis • Print Quality Assessment • Fundamentals • Determination on Optimal Coring Values • Preference Experiment • Conclusions • Future Work

  8. Determination onOptimal Coring Values

  9. Subjective Assessment • Objectives • To evaluate threshold of coring amount by psychophysical experiments • To determine limits of the coring algorithm that may cause unacceptable results • Environment • Equipments • HP Color LaserJet 2605 at printing resolution of 600 dpi • HP Color Laser Glossy Photo Paper 220 g/m2 • Normal ambient lighting condition in controlled laboratory

  10. Experimental Design • Pilot experiments • Test stimulus in the shape of annulus • Line widths between 5/600 inch and 50/600 inch • Nominal colorant levels between 90% and 100% in steps of 2.5% • Only combinations of cyan (C) and magenta (M) with same amounts 26 coring levels(Increasing order) 13 coring levels (Increasing order) 7 coring levels(Random order) 7 coring levels (Increasing order) 7 coring levels (Increasing order) 7 colorant levels (100% ~ 70%) 5 colorant levels (100% ~ 80%) 5 Colorant levels (100% to 90%) 5 colorant levels (100% ~ 90%) 5 colorant levels (100% ~ 90%) Pilot test 1 Pilot test 2 Pilot test 3 Pilot test 4 Pilot test 5

  11. Experimental Design (cont.) • Test pattern • Fixed nominal colorant level and fixed line width • Five repetitive trials • Randomly distributed over sets of test pages More coring for C and M • Symmetric coring More coring for C • Asymmetric coring More coring for M

  12. Experimental Design (cont.) Coring increases Coring of M increases Test pattern Varying nominal colorant level (fixed line width) Coring of C increases Skew mark Color planeregistration bars Calibration patches • Symmetric coring • Decreasing same amountsof C and M colorants • Perception of toner scatter • Asymmetric coring • Decreasing different amountsof C and M colorants • Perception of toner scatter • Color matching

  13. Experimental Design (cont.) • Charge to subject • View at normal viewing distance of 10 to 15 inches • Use apparatus to protect test page and facilitate examination of one test pattern at a time • Choose one test stimulus • Symmetric  leftmost one with no toner scatter • Asymmetric  one with no toner scatter and mostclosely matched color of thick border of solid colorant • Disregarded factors: Apparatus for symmetric coring Background noise Jaggedness Color plane misregistration

  14. Responses of Subjects Symmetric coring (25 subjects) Asymmetric coring (21 subjects)

  15. Optimal Coring Values • More coring for high colorant levels and thin lines • Less coring for low nominal colorant levels and wide lines • More coring for colorant M than colorant C except nominal colorant level 100% with thin line width

  16. Comparison with Bernal et al.’s Model • Difference • Line width: very thin and wide line widths (5 and 50 pixels) • Nominal colorant level: low colorant level (90%) • Basis of data for Bernal’s model • Monochrome softcopy experiments using blur in edges and lines • Obtained from two subjects

  17. Influence of Edge Directionon Toner Scatter • More coring for vertical than horizontal • Coring amounts for horizontal don’t depend on line width 10 subjects • Duration of toner stealing for vertical is longer than one for horizontal

  18. Influence of Edge Directionon Toner Scatter (cont.) Line width: 10 pixels, Nominal colorant level: 100% Printed at 600dpi, scanned at 1200dpi

  19. Outline • Remote Print Defect Diagnosis • Print Quality Assessment • Fundamentals • Determination on Optimal Coring Values • Preference Experiment • Conclusions • Future Work

  20. Preference Experiment • Objective • To evaluate whether human viewers prefer optimally cored prints over prints without coring in real-world images • Test material • Seven different page contents • Seven different nominal colorant levels (94%~100% in steps of 1%) • Asymmetric coring • Comparison • Control group: 10 subjects who participated in previous experiments • Experimental group: 10 new subjects who don’t know about coring • Charge to subject • Choose a page they prefer over another in terms of color and blur

  21. Preference Experiment (cont.) Test set

  22. Preference Experiment (cont.) • Results • Overall rate of preference to optimal coring over no coring: 98.57% • Group • Control group: 99.39% • Experimental group: 97.76% • Colorant level

  23. Conclusions • Subjects preferred • Less coring as colorant level decreases or line width increases • More coring for colorant M than colorant C • Vertical edges of text or characters provoke toner scatter easily than horizontal edges do • Confirmed that optimally cored prints were overwhelmingly preferred over non-cored prints

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