HDR

HDR may refer to:

Science and technology

Other uses

Dynamic range

Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest values of a changeable quantity, such as in signals like sound and light.

Definition

Dynamic range is the difference between the smallest and largest usable signal through a transmission or processing chain or storage medium. It is measured as a ratio, or as a base-10 (decibel) or base-2 (doublings, bits or stops) logarithmic value.

Dynamic range and human perception

The human senses of sight and hearing have a very high dynamic range. A human is capable of hearing (and usefully discerning) anything from a quiet murmur in a soundproofed room to the sound of the loudest heavy metal concert. Such a difference can exceed 100 dB which represents a factor of 100,000 in amplitude and a factor 10,000,000,000 in power. A human can see objects in starlight (although colour differentiation is reduced at low light levels) or in bright sunlight, even though on a moonless night objects receive 1/1,000,000,000 of the illumination they would on a bright sunny day: that is a dynamic range of 90 dB.

High-dynamic-range imaging

High-dynamic-range imaging (HDRI or HDR) 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. The brain continuously interprets this information so that most of us can see in a wide range of light conditions. Most cameras, on the other hand, cannot.

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. Non-HDR cameras take photographs with a limited exposure range, resulting in the loss of detail in highlights or shadows.