High-dynamic-range imaging (HDRI) is a high dynamic range technique used in imaging and photography to reproduce a greater dynamic range of luminosity than what is possible with standard photographic techniques. The aim is to present a similar range of luminance to that experienced through the human visual system. The human iris, adjusts constantly to adapt to a broad range of luminance present in the environment. The brain continuously interprets this information so that we can see in a wide range of light conditions.



Gustav le Gray was an early pioneer of photography wo noticed the limitation s of straight exposure. One could expose for the sky as he did in this first image:

But then the sea becomes almost black. One could expose for the sea as you see here:

But then the sky becomes washed out. However by taking a correct exposure for each and then combining the two in a single print Le Gray was able to make a perfect print image:

Ansel Adams later perfected another system of Dodging and Burning in order to acheive a similar effect in the Darkroom. In Ansels case he dodged light coming from the enlarger during exposure, that he wanted to be lighter. And he burned light that he wanted to be darker. In all of Ansel's prints elaborate dodging and burning techniques were utilized to best expose the different elements of his images to his eact specifications:

HDR images can represent a greater range of luminance levels than can be achieved using traditional methods, such as 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, referred to as LDR, resulting in the loss of detail in highlights or shadows.