Skyscrapers and Clouds

Here is a novel illusion that everyone can experience when the jagged contours of skyscrapers appear against the cloudy sky: with the clouds still behind, the skyscrapers contours appear to bulge out and the effect magnifies when the clouds move.
Most illusory distortions of parallel lines disappear if contours are jagged, but not our new illusion: we experience the “Skyscrapers and clouds” illusion because the visual system relies on local luminance contrast to code local tilts and positions along the contour bordered by a thin outline.

Read more about the illusion and possible explanations