HOW TO TELL RIGHT FROM LEFT

Many natural shapes have chirality (or handedness): for instance our hands have a right-hand version and a left-hand version, the two types being mirror images of each other. In chemistq, for example, molecules and crystals are classified as having chirality D or L. Interaction between molecules is dependent on their chirality, and chirality may determine chemical characteristics. For instance, only glucose of D-chirality is sweet, while gluwse of L-chirality is tasteless. We study the notion of chirality for two dimensional binary shapes, and introduce measures to test whether a shape is symmetric. and if not whether it is left-handed or right-handed. The measures are based on boundary analysis, and perform well even when digital images of left-handed shapes differ from the mirror images of right-handed shapes. Such situations may occur due to natural variations and digitization errors. The measures can also successfully treat partially occluded shapes, and provide indications on the change of chirality as resolution changes.