What is HDR?
A High Dynamic Range (HDR) image is an image that contains a larger range of color and tonality than typical files, which are known as Low Dynamic Range (LDR) images. HDR images are captured by special cameras or are created by merging multiple LDR images together. While LDR images normally contain either 8- or 16-bits per channel, HDR images contain 32-bits per channel.
Currently, there are no printers and only special monitors that can display HDR images. Therefore, in order to print or display an HDR image, they must be compressed down to an LDR image. This process, called tone mapping or tone compression, is one of the main processes that occurs in an HDR application such as HDR Efex Pro 2.
What is Dynamic Range?
In photography, Dynamic Range is the ratio between the minimum and maximum brightness values either of the original scene, the digital image, or of the final print.