1. HP - PURDUE CONFIDENTIAL Slide No. Fundamentals 1

2. HP - PURDUE CONFIDENTIAL Slide No. 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 2

3. HP - PURDUE CONFIDENTIAL Slide No. Toner Scatter 3 EP processEffect of toner scatter

4. HP - PURDUE CONFIDENTIAL Slide No. 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 4 Profile of cored line No coring18% coring50% coring Annulus with10-pixel width Printed at 600 dpi, scanned at 1200 dpi

5. HP - PURDUE CONFIDENTIAL Slide No. Overview of Coring (cont.) By utilizing both high and low resolution image data 5 Coring algorithm

6. HP - PURDUE CONFIDENTIAL Slide No. 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 6 No coringOptimally coredcolor clipped Printed at 600 dpi, scanned at 1200 dpi

7. HP - PURDUE CONFIDENTIAL Slide No. Outline Remote Print Defect Diagnosis Print Quality Assessment  Fundamentals  Determination on Optimal Coring Values  Preference Experiment  Conclusions Future Work 7

8. HP - PURDUE CONFIDENTIAL Slide No. Determination on Optimal Coring Values 8

9. HP - PURDUE CONFIDENTIAL Slide No. 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/m 2  Normal ambient lighting condition in controlled laboratory 9

10. HP - PURDUE CONFIDENTIAL Slide No. 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 10 7 colorant levels (100% ~ 70%) 26 coring levels (Increasing order) Pilot test 1 7 coring levels (Increasing order) 5 colorant levels (100% ~ 90%) Pilot test 4Pilot test 5 7 coring levels (Increasing order) 5 colorant levels (100% ~ 90%) Pilot test 2 5 colorant levels (100% ~ 80%) 13 coring levels (Increasing order) Pilot test 3 7 coring levels (Random order) 5 Colorant levels (100% to 90%)

11. HP - PURDUE CONFIDENTIAL Slide No. Experimental Design (cont.) 11 Symmetric coring More coring for C and M Asymmetric coring More coring for M More coring for C Test pattern  Fixed nominal colorant level and fixed line width  Five repetitive trials  Randomly distributed over sets of test pages

12. HP - PURDUE CONFIDENTIAL Slide No. Experimental Design (cont.) 12 Test pattern Calibration patches Color plane registration bars Coring increasesCoring of M increases Coring of C increases Varying nominal colorant level (fixed line width) Skew mark Symmetric coring  Decreasing same amounts of C and M colorants  Perception of toner scatter Asymmetric coring  Decreasing different amounts of C and M colorants  Perception of toner scatter  Color matching

13. HP - PURDUE CONFIDENTIAL Slide No. 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 most closely matched color of thick border of solid colorant Disregarded factors: 13 Background noiseJaggednessColor plane misregistration Apparatus for symmetric coring

14. HP - PURDUE CONFIDENTIAL Slide No. Responses of Subjects 14 Symmetric coring (25 subjects)Asymmetric coring (21 subjects)

15. HP - PURDUE CONFIDENTIAL Slide No. 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 15

16. HP - PURDUE CONFIDENTIAL Slide No. 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 16

17. HP - PURDUE CONFIDENTIAL Slide No. Influence of Edge Direction on Toner Scatter 17 More coring for vertical than horizontal Coring amounts for horizontal don’t depend on line width Duration of toner stealing for vertical is longer than one for horizontal 10 subjects

18. HP - PURDUE CONFIDENTIAL Slide No. Influence of Edge Direction on Toner Scatter (cont.) 18 Line width: 10 pixels, Nominal colorant level: 100% Printed at 600dpi, scanned at 1200dpi

19. HP - PURDUE CONFIDENTIAL Slide No. Outline Remote Print Defect Diagnosis Print Quality Assessment  Fundamentals  Determination on Optimal Coring Values  Preference Experiment  Conclusions Future Work 19

20. HP - PURDUE CONFIDENTIAL Slide No. 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 20

21. HP - PURDUE CONFIDENTIAL Slide No. Preference Experiment (cont.) 21 Test set

22. HP - PURDUE CONFIDENTIAL Slide No. 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 22 Colorant level (%) Number of chosen page Preference rate (%) No coringOptimal coring 1000140100 990140100 98113999.29 97113999.29 960140100 95213898.57 941013092.86 Total1496698.57

23. HP - PURDUE CONFIDENTIAL Slide No. 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 23