High-dynamic-range imaging is a technique used in imaging and photography to reproduce a greater dynamic range of luminosity than is possible with standard digital imaging or photographic techniques.
The aim is to present the human eye with a similar range of luminance as that which, through the visual system, is familiar in everyday life. The human eye, through adaptation of the iris (and other methods) adjusts constantly to the broad dynamic changes ubiquitous in our environment.

• In photography, dynamic range is measured in exposure value (EV) differences
• High-dynamic-range photographs are generally achieved by capturing images
• To reveal detail in the darkest shadow requires high exposures.

HDR images can represent a greater range of luminance levels than can be achieved using more ‘traditional’ methods, such as many real-world scenes containing very bright, direct sunlight to extreme shade, or very faint nebulae. This is often achieved by capturing and then combining several different narrower range exposures of the same subject matter.
Also, as one must create several images (often three or five-sometimes more) to obtain the desired luminance range.