The Chubb illusion is an optical illusion wherein the apparent contrast of a patterned object varies dramatically, depending on the context of the presentation. (New world encyclopedia)
An object of low-contrast visual texture surrounded by a field of uniform visual texture appears to have higher contrast than when presented on a field of high-contrast texture. This illusion was observed by Charles Chubb and colleagues and published in 1989. The Chubb illusion is similar to another visual illusion, the contrast effect. (Wikipedia)
Low-contrast texture surrounded by a uniform field appears to have higher contrast than when it is surrounded by high-contrast texture.
Lotto and Purves (2001) demonstrated that the Chubb illusion can be explained "by the degree to which imperfect transmittance is likely to have affected the light that reaches the eye." www.mind.duke.edu. Indeed, these observations suggest a wholly empirical explanation of the Chubb illusion.
Additional images and explanation:
www.purveslab.net www.journalofvision.org www.illusionism.org