The light in nature has very wide range of intensity of light. It is from the light that only can be seen by specific equipments to the light that is too intense so that humen can't see it easily.

Screens such like computer monitors never have the range in nature. For instance, when you see the movies in theater, what happened if the theater is bright? In that circustance, because the black point is seen as white or gray point, the range of beteween darkest and brightest color is very narrowed - this range is called the contrast.

However, light of  the projector in theater is very weak. The light of the theater cannot be as bright as the light in nature. Computer monitors are worse than that. Its contrast is merely about 1:1000. Simulating and supporting brighter light is the HDR. Including computer hardware, HDR chagnes the image for display, so as if the part of image is more brighter than actually seen. Following picture is the screenshot in Half-life 2 Lost Coast(Blog link)


In this picture, we can see the part of stairs is overlapped by distant light of sky. Sky is too bright, bright part is spread out by the light color of sky. HDR not only make the brighter part wider, but also reflect the brighter part through the water more obviously. So you may think that reflected part is brighter than others.[1]



(Larger images are in the site of references) You can see that brighter part of sky is spread out and this part is reflected clearly. There are many other effects, such as the effect that make the brighter part vivid.[2]

However, there is the effect, had same name as HDR, performs conversely.[3] Though computer simulations like above effects make narrow range of light wider, HDR in Photography condensates wide range of light(of nature) into the the narrow range of pictures.


Let me show the example. The left picture is taken in low exposure. So brighter part of sun is obvious, but darer park of the water is barely seen. Picture of center is taked in high exposure, and expressed conversely.
The right picture is composed of two pictures. Beacause of the limitation of film or CCD, pictures taken by camera cannot have wide range of exposure. So from the two pictures, you can have the clear and vivid picture.

There are side effects! Because of overuse of HDR, screen in like games, is opaque or misty. And on film of camera dicrector who is working with Steven Spielberg, these days, I think these effect are overused. In the game, Rainbow Six - Vegas, this effect is too overused, so that even just white paper in a room is shine without any special devices. This means that objects in the game have no any other information about the HDR, and HDR is imposed into just normal objects.

These pictures are form the movie, 'War of the Worlds' (Click it, if you want larger images) First image is about the HDR of asphalt, second and third images are as if computer graphics are used all over screen. Effect is very overused. Though Speilberg may like this effect, I don't like this exaggeration.

In spite of these side effect and disadvantages of performance in games, HDR is very popular and very noticed in game graphics. Because both of DirectX and Graphics Card suport HDR so that it can be used easily and make the game graphics much better, there are few reasons that we can't use it.

ps. I just described some of HDR. There are other effects about HDR such like Motion Blur of HDR. If you want more informations about HDR, you can get them from references.

References & Pictures
[1] : Wikipedia - High Dynamic Range (Accurate representation of light)
[2] : Wikipedia - High Dynamic Range (Preservation of detail in large contrast differences)
[3] : HDR Photography in Photoshop CS2

Footnote
[4] : As I know, Speilberg have been working with this camera director from the movie, 'Saving Private Ryan(1998). Whole screen is rough and blurred like computer graphics. Because of this, Computer graphics of movies is barely noticed.

* 이 글은 'HDR (High Dynamic Ragne) 란?' 을 영어로 번역한 글이다. 오타나 잘못된 표현은 생각보다 많을지도..
* 오타를 지적해주신 Hsd님께 감사드립니다~

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