Sunday, February 18, 2007

Readability of colored text on a colored background

We have all encountered Web pages with colored text on a colored background that gave us trouble. Sometimes they were hard to read, especially for those of us with color vision deficiencies. Other times we could read them, but we felt irritated. Did you know you can do something about it? Read on to find out how. The readability of text for readers with normal vision, low vision, or color vision deficiency (CVD) has been studied for decades by Gordon Legge and his coworkers at the University of Minnesota. However, most of their color work is for monochrome displays with colored phosphors. The W3C has proposed recommendation for the accessibility of Web pages based on new work that does not build on the current knowledge.

In 2005 the Italian Government, specifically the Ministero per l'Istruzione, le Università, e la Ricerca (MIUR) instructed the company designing its Web sites to revise the pages to conform to the W3C recommendation. This company, Vocabola in Venice, quickly found out that recommendations correlate very poorly with perceptual readability.

True to their passion, Vocabola set up a Web site to discuss this problem,, which soon showed that most experienced Web designers agree that the W3C recommendation is misguided. However, nobody in their circle knew how to solve the accessibility problem. This is when Silvia Postai, Vocabola's owner of Vocabola and author of the Italian bible for Web designers, contacted the well known color researcher Silvia Zuffi at the Centro Nazionale per la Ricerca (CNR) in Milano and also professor at the university Milano-Bicocca. Silvia at that time was working on a color selection tool for Web designers.

Silvia remembered I had shown a program addressing this problem at the AIC meeting in Granada earlier that year [for you managers among the readers: see, this is why we have to attend conferences], so she contacted me. Silvia enlisted the help of a well known mathematical statistician, Carla Brambilla, and they performed a psychophysics experiment for estimating the contrast requirement. The results were published in HPL-2005-216.

Silvia then had the idea that this problem would be ideal to attempt a psychophysics experiment on the Web, as they have been tried a few times before. Silvia and Carla repeated the traditional experiment und very tightly controlled conditions to have a reference point. Then they designed a Web version and determined that the two experiments yield the same predictions. This was described in HPL-2006-187.

Contrast is only one dimension, and the data can be used to determine other factors determining the visual quality of a Web page. This is where you can help.

One would expect that on the Web one would get orders of magnitude more data than one can get from a controlled experiment. However, as others who have done psychophysics on the Web have experienced, only few people actually contribute data and a large percentage of the data in unusable. To help, please visit the Web page for the experiment and give us at about an hour of observations, i.e., try to do about 50 repetitions. Then let a friend know and have them also contribute. The URL is

We are also very interested in hearing your suggestions and comments. Please use the comment feature in this blog to let us know how this work can be improved.

PS: Links contributed in comments: