Introduction

Why do we interpret stimuli arriving at our retina as straight lines, squares, circles, and any kind of other familiar shape? This question may look incongruous: What is more natural than recognizing a “straight line” in a straight line image, a “blue cube” in a blue cube image? When we believe we see a straight line, the actual stimulus on our retina does not have much to do with the mathematical representation of a continuous, infinitely thin, and straight stroke. All images, as rough data, are a pointillist datum made of more or less dark or colored dots corresponding to local retina cell stimuli. This total lack of structure is equally true for digital images made of pixels, namely square colored dots of a fixed size.