HDR which stands for High Dynamic Range simply means that the range of luminosity in a photo is higher than typical display device (like LCD at the back of your camera or monitor on your desk) is capable of displaying. These devices are very limited and cannot show all the luminosity we observe with our eyes in reality. Besides our cameras cannot capture this luminosity (take a photo of a scene having deep shadows and very bright light at the same time – you’ll end up with some parts highly underexposed or overexposed thus loosing details in highlights or shadows) even when shooting in RAW format which is much much better in this regard when compared to JPG. Our eyes do see in HDR. It’s our photography equipment that doesn’t.
So HDR photography is a way to trick these devices to make them see what we do. Instead of capturing a single photo we take multiple shots with different exposure settings to have photos with shadows perfectly exposed, with midtones perfectly exposed and highlights perfectly exposed. The higher the contrast of original scene, the more photos we have to take to fully cover this range. Then these different exposures are merged into one high dynamic range photo.
But such HDR photo cannot be displayed on current display devices (as there will be large regions of “over” or “under” exposed pixels) as normally the HDR photo have 96-bit depth (compared to 24-bit depth of a typical monitor). That’s where tone mapping comes into play. Tone mapping is an operation which “maps” high dynamic range photo to a limited range our monitor can display. It means it throws some of the information away and takes best part of each photo (it’s much more complex in fact). Tone mapping in most HDR software is highly customizable process allowing you to decide on how this mapping should be performed. It is this step that might make the photo artificial or natural. It is tone mapping that might result in artificial results. So it’s only about the tone mapping skills of photographer not about HDR photography as a whole.
Below I put example HDR photos I shot recently. Do they look natural or artificial to you?