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High dynamic range (HDR) is a post-processing method used in imaging and photography for adding more "dynamic range" (ratio of light and dark) in a photograph in order to mimic what a human eye can see. The human eye can see details even if the scene has both light and dark areas, whereas a camera will often have a large contrast between these areas, resulting in darker shadowy areas having less detail because it would be mainly dark. HDR mimics how our eyes perceive the dynamic range by giving more detail to dark areas. This is done by merging photos of the same subject taken with different exposures.
High-dynamic-range imaging has been around nearly as long as photography itself and was pioneered by Gustave Le Gray as early as the 1850s in order to render seascapes that could show both the sea and the sky. Taking a single photo that shows both the sky and the sea was impossible at the time because the technology could not compensate for the extreme range of difference in luminosity between the two subjects. Le Gray had the idea to take different pictures for each subject and later combine them in a single negative to get the effect. He used one negative of the sky and another negative for the sea taken with a longer exposure.
With the advent of digital imaging software and digital cameras, HDR imaging became more prolific as it became easier to take photographs with multiple exposures and then combine them during post-processing using imaging software. But in recent years, with the great leap in mobile technology and software, HDR imaging is slowly transforming into HDR photography as modern mobile devices such as cell phones and modern digital cameras can perform the whole process, from taking different pictures with different exposures to combining them into a single image, in a single press of a button. No longer do users need to get on their computers, download the images and then meticulously slice and crop the images to get the HDR image they want, because the entire process is done via the camera's image processing software. In the case of cellular phone implementations, three pictures of different exposures are taken and combined. The process is slightly different for each camera application, and, combined with the capabilities of the camera, the quality of the result can vary.