Editing Multiple exposure (section)

==Overview==
Ordinarily, cameras have a sensitivity to light that is a function of time.  For example, a one-second exposure is an exposure in which the camera image is equally responsive to light over the exposure time of one second. The criterion for determining that something is a double exposure is that the sensitivity goes up and then back down. The simplest example of a multiple exposure is a double exposure without flash, i.e. two partial exposures are made and then combined into one complete exposure.
Some single exposures, such as "flash and blur" use a combination of electronic flash and ambient exposure. This effect can be approximated by a [[Dirac delta measure]] (flash) and a constant finite rectangular window, in combination. For example, a sensitivity window comprising a [[Dirac comb]] combined with a rectangular pulse, is considered a multiple exposure, even though the sensitivity never goes to zero during the exposure.