Frequently Asked Questions About HDR Images:
HDR stands for High Dynamic Range and are sometimes referred to as HDRI or High Dynamic Range Images. It’s a method of photography that exposes both dark and light values of an image.
For example, if you take an ordinary photograph of an interior room facing a window, the room will be properly exposed but everything outside the window will be “blown out” or overexposed with white. On the other hand, if you take the same picture with the focus set outside of the same window, the interior will be very dark or underexposed.
In contrast to ordinary photographs, the human eye naturally exposes both the light and dark values of a room with a window view. Presently, cameras cannot intelligently distinguish these differences. HDR circumvents these limitations.
How HDR Works:
HDR images are processed by taking multiple exposures or intervals from the same camera angle. These range from extremely dark to very bright. Then they are combined using processing software. The end result allows us to accurately control the highlights and dark values (exposure.) This creates a more accurate photograph which circumvents limitations of traditional photography. HDR software guesses or “extrapolates” information beyond ordinary photographs (also known as Floating Point data.)
Our HDRIs attempt to mimic real-world conditions as seen through the human eye. This is for the purposes of lighting 3D renderings. This is the original purpose of the HDR format. Many photographers have come to discover that they can take HDRs and create unusual (and sometimes unrealistic) results with further adjustments and tweaks.
Realistic vs. Unrealistic HDR Images:
HDR style for general photography is a matter of preference and a source of debate. I’ve seen “overcooked” HDRs, but also some photographs that turned out absolutely astounding. For 3D applications, we attempt to achieve more natural results that mimic real world environments and conditions.
These photos involve stitching multiple photographs and exposures together to create a 360-degree panoramic format. This envelopes a 3D scene with light. These elongated HDRs (also known as equirectangular formats) are the most commonly used format for 3D HDR lighting.
Additional General HDR Information and Resources:
A Google search for “HDR” or” HDRI” will turn up hundreds, if not thousands of results these days. For a good start, I’d recommend exploring the following sites:
High Dynamic Range Images on Wikipedia.
HDRlabs: A comprehensive resource and forum on sIBL and HDR started by Christian Bloch.
The HDRI Handbook: One of the first HDR books also written by Christian Bloch.