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14:3 Ensure that Images Do Not Slow Downloads

Relative Importance:

Relative Importance rating of 4 out of 5

Strength of Evidence:

Strength of Evidence rating of 4 out of 5

Document Type: Guideline


Topic:

Graphics and Images


Guideline:

Take steps to ensure that images do not negatively impact download speeds.


Comments:

Delays are frustrating to users. Strive to maintain download speeds to less than five seconds. To improve download speeds, use several small images rather than a single large image. Repeat images when possible, and save images with the “interlaced” or “progressive” option. Limit page sizes to less than 30,000 bytes. Minimize the number of different colors used in an image, and add pixel dimension tags (e.g., height and width) to the image reference.

High Speed users may not notice anything different; however, these techniques will greatly improve download speeds for modem or hotspot users. 

 

 


Sources:

  • Bouch, A., Kuchinsky, A., & Bhatti, N. (2000). Quality is in the eye of the beholder: Meeting users’ requirements for internet quality of service. Proceedings of CHI 2000, 297-304.
  • Farkas, D.K. & Farkas, J.B. (2000). Guidelines for designing web navigation. Technical Communication, 47(3), 341-358.
  • Marchionini, G. (1995). Information Seeking in Electronic Environments. New York: Cambridge University Press.
  • Martin, G.L. & Corl, K.G. (1986). System response time effects on user productivity. Behaviour and Information Technology, 5(1), 3-13.
  • Nielsen, J. (1996a, May). Top ten mistakes in Web design. Retrieved November 2005, from http://www.useit.com/alertbox/9605.html.
  • Nielsen, J. (1997a, March). The need for speed. Retrieved November 2005, from http://www.useit.com/alertbox/9703a.html.
  • Nielsen, J. (1999c, May). The top ten new mistakes of Web design. Retrieved November 2005, from http://www.useit.com/alertbox/990530.html.
  • Nielsen, J. (2000). Designing Web Usability. Indianapolis, IN: New Riders.
  • Perfetti, C. (2001, January). The truth about download time. Retrieved November 2005, from http://www.uie.com/articles/download_time/.
  • Ramsay, J., Barbesi, A., & Preece, J. (1998). A psychological investigation of long retrieval times on the World Wide Web. Interacting with Computers, 10, 77-86.
  • Schroeder, W. (2003, April). Usability myths need reality checks. User Interface Engineering Newsletter. Retrieved November 2005, from http://www.uie.com/articles/usability_myths/.
  • Sears, A., Jacko, J., & Borella, M. (1997). Internet delay effects: How users perceive quality, organization and ease of use information. Proceedings of CHI’97, 353-354.
  • Selvidge, P.R., Chaparro, B.S., & Bender, G.T. (2001). The world wide wait: Effects of delays on user performance. International Journal of Industrial Ergonomics, 29(1), 15-20.
  • Shneiderman, B. (1984). Response time and display rate in human performance with computers. Computing Surveys, 16, 265-285.
  • Tullis, T.S. (2001). Web usability lessons learned. Fidelity Center for Applied Technology Technical Report. Fidelity Investments.

Poor Example:

The highlighted section is a large image. To improve this section use HTML for the background (if necessary) and text portion, leaving only the smaller images.

14_03_bad_example