Scientists have been looking into the phenomenon of why our fickle eyes and minds play tricks on us. Have you ever seen a photograph that looks like the subject has just been cut and pasted in? Remember the notorious "the dress" debacle that divided the world back in 2015? It turns out, it’s all to do with lighting and our brain jumping to conclusions.
Researchers in the UK looked at this photo (above) of a 75-meter-long (246 feet) public art piece by Nayan Kulkarni called Blade in the city center of Hull, UK, released by the city last year. Many people immediately suggested the object appeared superimposed.
“I saw pictures of the installation in the media, and at first sight, the photographs seemed to be clumsy fakes,” George Mather, Professor of Vision Science at the University of Lincoln, said in a statement. “Something else seemed to be at work too, at least to my eyes as a vision scientist."
"The blade appeared to be a cylindrical object, strangely out-of-keeping with the local environment, lit differently, as though it was superimposed on the scene digitally, but it really was there," he added.
In the study, published in the journal i-Perception, Mather and his colleagues explain how it’s all to do with the reflection of light and how we perceive it. We make judgments of how objects should appear, based on our pre-conceived notions of the object’s shape, texture, surrounding light source, the wider visual context, etc.
However, it isn’t always possible to accurately convey all this information in a two-dimensional photograph, which can make your perception generate some misconceptions about how light is falling on an object. For example, with Blade, the picture doesn’t show that one side of the blade is convex and concave on the same surface, in an S-shape. Daylight is actually hitting the object from above, which produced shading, creating the illusion that the blade is cylindrical and is being illuminated from the side.
The researchers tested out this idea by creating a series of digital images that showed a cylindrical C-shaped profile and a more complex S-shaped profile, producing images of each shape lit from above and the front. The images demonstrated that the S-shape when lit from above and the C-shape when lit from the front both appeared cylindrical.
This is a similar phenomenon to the notorious color-shifting dress image that went viral in 2015. In this instance, our brain makes assumptions on the type of light falling onto the dress. If people imagine the dress is in a brightly light room with blue-ish artificial lighting then our brain attempts to account for this and will “remove” the blue as a possible shadow.