Multiple exposure

This effect can be approximated by a Dirac delta measure (flash) and a constant finite rectangular window, in combination.

In the historical technique of chronophotography, dating back to the Victorian era, a series of instantaneous photographs were taken at short and equal intervals of time.

The technique is sometimes used as an artistic visual effect and can be used to create ghostly images or to add people and objects to a scene that were not originally there.

In some conditions, for example, recording the whole progress of a lunar eclipse in multiple exposures, a stable tripod is essential.

Digital technology enables images to be superimposed over each other by using a software photo editor, such as Adobe Photoshop or the GIMP.

[2] In addition to direct photographic usage of the technique, fine artists' work has been inspired by the multiple exposure effect.

Examples include Joan Semmel's oil on canvas "Transitions" from 2012,[3][4] and Ian Hornak's acrylic on canvas "Hanna Tillich's Mirror: Rembrandt's Three Trees Transformed Into The Expulsion From Eden", from 1978 (depicted below).

Among the scanning software solutions which implement multiple exposure are VueScan and SilverFast.