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HDR Photography

31.01.2008 Category: Photography Tutorials

Nikolai Church (HDR photography)

Picture 1. An example of the result of HDR photography: Nikolai church at night.

The acronym HDR comes from the words High Dynamic Range. In a photo, dynamic range means the difference between the lightest and the darkest color value. In other words, dynamic range means the contrast of a photo. HDR photo means a photo which has larger dynamic range than an ordinary photo. HDR photos have larger dynamic range than today's digital consumer cameras are able to capture.

I would still like to clarify what isn't an HDR photo, because the term HDR photo is often used wrongly especially in the Internet. In the Internet, you often see a photo which is said to be an HDR photo. That is misleading because almost always the photo in question is an ordinary photo which is created from an HDR photo. The photo might look really special or unreal and its probably an appropriate result of an HDR technique, but its not exactly an HDR photo. The actual HDR photo is something that you only rarely found in the Internet and something that browsers can't even display. It seems that usually when people talk about HDR photos in the Internet they actually mean a normal photo (LDR) which is created from an HDR photo. Still, I think its important to understand the real and literal meaning of the term HDR photo.

The Meaning of High Dynamic Range Imaging in Photography

Some people might think that the purpose of HDRI is to produce unrealistically colorful, flat, or artistic photos. In my opinion the real purpose of HDR photography is to produce a photo, the quality of which is higher than that of a normal photo(LDR). The purpose of HDRI is to overcome the limitations of camera equipment. HDR photography has the following advantages when compared to normal photography:

HDR Photography Captures Higher Dynamic Range

Let's imagine a situation where one photographs (without a flash) a high contrast scene where the subject is against the sky. Typically there is a problem in the result. Either the sky is too bright (over exposed), or the subject is too dark (under exposed). That doesn't equal to what was seen with eyes. Eyes can see details in both the subject and the sky clearly. Normal digital camera isn't able to see as high contrast as a human eye is. In other words a digital camera isn't able to capture as high dynamic range as a human eye is able to see.

An HDR photo can have a very high dynamic range which makes it possible to capture scenes with extremely high contrast. HDR photo can include all the details that a human eye is able to see. In photography, the goal is often to capture the view and the mood that was seen and experienced. Unfortunately, because of the limitations of digital cameras, some details are often missing in photos. In high contrast scenes, a digital camera isn't able to capture both the brightest and the darkest areas simultaneously. HDR photography offers a solution to this problem.

The high dynamic range and the way HDR photo saves image information, give new possibilities to digital image processing. One can do very strong digital image processing operations to an HDR photo without loosing any image information. Properly created HDR photo can include very large amount of image information and therefore give photographer a possibility to create exactly the kind of photo he wants.

HDR Photography Can Produce Noise Free Photos

An HDR photo is created by merging several photos that are taken with different exposures. If there are enough exposures, each part of the photo has optimal exposure in several shots. I don't know the merging algorithms of HDR programs but presumably they take best parts of the photos and / or do some averaging between the pixels in different shots and therefore noise is reduced effectively. Anyway, according to my tests HDRI makes it possible to produce photos that are noise free even in the darkest shadows.

HDR photo of cathedral of Uspensky

Picture 2. HDR photography can produce noise free photos.

My HDR tutorials