Chiaroscuro is an art term used to describe the appearance of light and dark tones in a picture. It’s correctly (and quickly) pronounced “kee-ah-ro-skoo-ro”. It’s based on words in the Italian language: chiaro means clear, light or bright and scuro means dark, dull or obscured.
The term has been traditionally used to describe the technique a painter uses to create the illusion of three-dimensional volume with light and dark paints. This is done by making one side of an object appear brightly lit and the other in shadow, as objects often do in the real world.
A strong treatment of chiaroscuro usually results in pictures with high contrast and dramatic appearance of depth, dimension and texture. Conversely, a picture without chiaroscuro is relatively flat and low contrast. Technically, chiaroscuro refers only to value (or tone) and is irrespective of the hue or color component. However, chiaroscuro can be evident in both black-and-white and color pictures.
Although the term most typically applies to painting technique, chiaroscuro can also be identified in the representation of objects within a photograph. Both of the sample images to the right have a lot of chiaroscuro present (click for larger versions).
The next time you’re viewing a painting or photograph, try to determine if the picture contains a high or low degree of chiaroscuro. You can read more about it in this Wikipedia article.