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High Dynamic Range Imaging

What is High Dynamic Range Imaging?

Jake Smith

on 27 April 2010

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Transcript of High Dynamic Range Imaging

High Dynamic Range Imaging By Jake Smith Traditional Imaging has some problems
associated with it. One of these problems is in capturing acurately the correct Luminances in both the lightest and darkest areas of a photograph. There is a wide range of intensity in real scenes. HDR seeks to capture
the darkest areas
and the brightest areas
just like in real scenes. There are general ways to capture an HDR image. 3 Computer
Renderings Multiple
Capture In-camera
Pixels Computers can render a scene with lighting calculations at increased range. This is a common technique because rendering without HDR
leaves the images dull, unrealistic, and without a light bloom. Using HDR allows for realistic reflection, refraction, and transparency. Bright objects such as the sun are not saturated to a brighness value of 1.0
This means that a 30% reflection can look realistic. These developments can be attributed to a few papers: Nakamae, E., Kaneda, K., Okamoto, T., and Nishita, T. 1990. A lighting model aiming at drive simulators. In Proceedings of the 17th Annual Conference on Computer Graphics and interactive Techniques (Dallas, TX, USA). SIGGRAPH '90. ACM, New York, NY, 395-404. Spencer, G., Shirley, P., Zimmerman, K., and Greenberg, D. P. 1995. Physically-based glare effects for digital images. In Proceedings of the 22nd Annual Conference on Computer Graphics and interactive Techniques S. G. Mair and R. Cook, Eds. SIGGRAPH '95. ACM, New York, NY, 325-334. Paul E. Debevec and Jitendra Malik. Recovering High Dynamic Range Radiance Maps from Photographs. In SIGGRAPH 97, August 1997. Paul E. Debevec. Rendering Synthetic Objects into Real Scenes: Bridging Traditional and Image-Based Graphics with Global Illumination and High Dynamic Range Photography. In SIGGRAPH 98, July 1998. By 2004 and DirectX 9.0c, most 3d video games used this technique. In photography, dynamic range is measured in EV differences (known as stops)
between the brightest and darkest parts of the image that show detail. An increase of one EV, or one stop, is a doubling of the amount of light. Any camera that allows manual over- or under-exposure of a photo can be used to create HDR images. One common method is to take 5 photos:
one at the best exposure ISO, then one at two stops below (-2), then also (-4), (2), (4). Here's an example. Multiple image capture method by Kevin McCoy
(Source: Wikipedia) Double under-exposure (-4.72) Single under-exposure (-1.82) "Best" exposure (+1.18) Single over-exposure (+1.51) Double over-exposure (+4.09) These 5 photos get combined. They're contrast is reduced,
leaving an LDR image. Simple contrast reduduced HDR, or CDR Local tone-mapped HDR This is also known as
Compressed Dynamic Range (CDR). The photo can use "local" levels to map tones,
thus producing an almost surreal image. Gustave Le Gray pioneered the multiple image capture concept in the 1850s. Charles Wyckoff tone-mapped nuclear explosions for LIFE in the 1940s. Gregory Ward created the Radiance RGBE image file format, the first and still most widely used, in 1985. Steve Mann and Rosalind Picard presented a mathematical theory of differently exposed images in 1995. Paul Debevec introduced a theory to combine several
differently exposed images in 1997. Since CS2, Adobe Photoshop has the ability to merge to HDR. There is somewhat of a problem with the
multiple image capture method. It takes a long time. To solve this problem, camera companies are developing ways to take multiple exposures all at once. Fuji's SuperCCD S3 Pro Most high-end cameras nowadays will
have at least a pseudo-HDR method. There's even an "HDR" iPhone app. This is not an in-camera hardware solution,
but it is making HDR accessible. Here is an effort of mine to recreate the results. Photomatix remains the industry standard Wrong ISO and clouds moved Better, but still not good 5 different exposures, none great HDR, but still flat color Much better color, surreal look Best normal settings HDR, better color Tone Mapped Another look, tone mapped Flat color Slightly more vibrant HDR Tone mapped Is it day or night? Too bright for the light Can see tiles, but boring color Tone mapped to make it even color everywhere Normal HDR, great color Surreal tone mapping Highlighting Conclusions 1. The sky is hard to deal with.
2. Bring a good tripod with a remote.
3. 7 pictures is not significantly better than 3.
4. Adjusting a local adaption (tone map) is an art.
5. HDR is a labor-intense hobby.
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