Assessing Lag Perception in Electronic Sketching

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Electronic sketching has received a recurrence of interest over the years and again nowadays within the mobile web context, where there are diverse devices, operating systems and browsers to be considered. Multi-platform (e.g. web-based) sketching systems can be constructed to allow users to sketch on their device of preference. However, web applications do not always perform equally on all devices, and this is a critical issue, especially for applications that require instant visual feedback such as sketch-based systems. This paper describes a user study conducted to identify the most appropriate response rates (expressed in frames per second) for end users while sketching. The results are expected to guide stakeholders in defining response parameters for sketching applications on the web by showing intervals that are accepted, tolerated, and rejected by end users.
  • 1. Assessing Lag Perception inElectronic Sketching Ugo Braga Sangiorgi Vivian G. Motti François Beuvens Jean Vanderdonckt Louvain Interaction Laboratory, Université catholique de Louvain - Belgium
  • 2. Agenda• The lag problem• Sketching on many devices• Experiment• Results• Conclusion 2
  • 3. What makes a device un/suitable for sketching? 3
  • 4. Lag 4
  • 5. Lag in electronic sketching 133 points 60 Hz 60 FPSper second 75 Hz 75 FPS … … 5
  • 6. Refresh rate• Example: http://frames-per-second.appspot.com/• 30 FPS o (1000/30) = 33 miliseconds 6
  • 7. Sketching on many devices• HTML5 7
  • 8. Sketching on many devices • HTML5 • 1.4 devices per person by 2016 11 - CISCO‟s Visual Networking Indexhttp://www.ciscovni.com/vni_forecast/index.htm 8
  • 9. Sketching on many devices • HTML5 • 1.4 devices per person by 2016 1 • Design interfaces o Diverse context o Weight, screen types o E-paper?1 - CISCO‟s Visual Networking Indexhttp://www.ciscovni.com/vni_forecast/index.htm 9
  • 10. Devices 10 FPS 25 FPS 45FPS 15 FPS 21 FPS 10
  • 11. Benchmark 11
  • 12. Why?• Developers would know what to do o Respond accordingly o Keep the refresh rate low• Discard some devices o Activities o User profiles 12
  • 13. Experiment• What is the FPS rate at which the users start to perceive the system as „too slow‟?• Three phases• Draw squares and grade the speed. 13
  • 14. Subjects• 35 users recruited around the campus. o 16 women, 19 men o Avg. 28 years old• Different nationalities• Different fields of expertise o Biology, Psychology, Computer Science, Management, etc. 14
  • 15. Material• Wacom Cintiq12 o 75 Hz (upper limit of 75 FPS)• MacBook pro 2.9GHz• http://exp.gambit-sketch.appspot.com (be nice) 15
  • 16. Two groups 16
  • 17. 1st phase • A vs B comparison • “Are the response rates different?” • Goal: find out if users perceive small or large differences 17
  • 18. 1st phase 18
  • 19. 1st phase 19
  • 20. Results: 1st phase 20
  • 21. Results: 1st phase • Not conclusive 21
  • 22. 2nd phase • Likert scale grading • “How happy are you with this response rate?” • Goal: find out when the users start to grade as “bad” and “really bad” 22
  • 23. 2nd phase 23
  • 24. Results: 2nd phase 24
  • 25. Results: 2nd phase 25
  • 26. Results: 2nd phase 26
  • 27. 3rd phase • Active selection of a preferred response rate • “What is the minimum in your opinion?” • Goal: cross-validate the 2nd phase 27
  • 28. Results: 3rd phase 28
  • 29. Findings• The range below 20 FPS was rejected by users;• The difference between grades is not significant above 24 FPS• No conclusive evidence that subjects perceived differences of 2, 5 and 10 FPS when testing pairs of rates 29
  • 30. Next steps• Writing activity• Specific types of professionals o Designers o Architects o Non-drawing professionals 30
  • 31. Thank you• Ugo.Sangiorgi@uclouvain.be• @ugosan 31
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