HDR - High Dynamic Range Imaging
March 13th, 2008 | Posted in Images/Photos |
Photo source: Abduzeedo.com
High Dynamic Range Imaging (commonly referred to as HDR) is an exciting, emerging technology that should be closely monitored over the next few years. Quite honestly, HDR is on the brink of changing the way we capture, manipulate, store, use, and display images for the foreseeable future. With that being said, let’s delve into HDR a little bit so that we can gain a little better understanding of this promising technology.
So, what exactly is HDR? The following is an excerpt from Wikipedia that gives a brief, but good definition of HDR:
“High dynamic range imaging (HDRI) is a set of techniques that allows a greater dynamic range of exposures (the range of values between light and dark areas) than normal digital imaging techniques. The intention of HDRI is to accurately represent the wide range of intensity levels found in real scenes ranging from direct sunlight to shadows.
HDRI was originally developed for use with purely computer-generated images. Later, methods were developed to produce a high dynamic range image from a set of photographs taken with a range of exposures. With the rising popularity of digital cameras and easy-to-use desktop software, the term “HDR” is now popularly used to refer to the process of tone mapping together with bracketed exposures of normal digital images, giving the end result a high, often exaggerated dynamic range. This composite technique is different from, and generally of lower quality than, the production of an image from a single exposure of a sensor that has a native high dynamic range. Tone mapping is also used to display HDR images on devices with a low native dynamic range, such as a computer screen.”
HDR gives the photographer the ability to create a greater range of detail than any camera could ever capture in a single photo. The “merge to HDR” feature of Photoshop CS3 allows the photographer to combine a series of exposures into a single image which contains the details of the entire set of images. Photomatix is another HDR software program that allows the photographer the ability to synthesize and manipulate a series of images into one HDR image. As with any type of software, there will be people devoted to one or the other. In our particular case, we are just offering up the two most commonly used programs for creating HDR images.
Dynamic range (DR) consists of luminance values from the darkest to the brightest. An original, real-world scene has a certain, inherent DR which may be quite large – perhaps a ratio of 100,000:1 or more. The human eye can perceive a subset of any scene’s DR (about 10,000:1); a camera can record a smaller subset than your eyes – perhaps 400:1 for a DSLR. The DR of a computer monitor or a printed photograph is still smaller yet.
High dynamic range (HDR) in photography means the full range of tonality present in a scene with high perceptual accuracy. Current HDR techniques use computer software, such as Photoshop CS3 or Photomatix, to combine several exposures of a scene into a single file that displays the full range of luminance at every pixel. This HDR image can then be processed in various ways, contingent upon its ultimate usage. For most, at the moment, it means tone mapping the HDR image into a 16-bit or 8-bit digital file such as a JPEG or TIFF. The standard unit for measuring luminance is candelas per square meter, or cd/m2. You may have seen this unit used in monitor specifications. According to the FAQ at www.hdrsoft.com (the web site for Photomatix Pro), “the luminance of starlight is around 0.001 cd/m2, that of a sunlit scene is around 100,000 cd/m2, [… and] the luminance of the sun itself is approximately 1,000,000,000 cd/m2.”
Photo source: Abduzeedo.com
Judging from this information then, one can say that the experience of seeing the original scene, then capturing it, and reproducing it for others to see, is a process that progressively loses DR. In this case, HDR gives the photographer the ability to capture and represent the full DR found in a particular scene with a high degree of accuracy and precision.
Photo source: Abduzeedo.com
Why is HDR necessary and what use is it to me?
HDR is still emerging. Photographers are only now really beginning to work with it in large scale numbers. HDR has a great future since it can (if applied correctly) reproduce a scene that has been observed from a human perspective more accurately than any other image format in history. As for its uses currently? The best answer for that one may be “artistic expression.” Photographers have been introduced to a new, powerful tool that, in addition to typical photo manipulation techniques of the past, allows them to push the envelope of manipulating images even further. HDR allows photographers the ability to recreate a scene more accurately than ever before, or simply create their own twist on a captured slice of reality. At this point, the possibilities and development potential are wide open – making it an incredibly exciting format to keep an eye on! Right now, keep the phrase, “for your viewing pleasure” in the back of your mind and enjoy looking at the creativity behind the images.
Where does HDR go from here?
Well, it may sound cliché, but the sky’s the limit. Advances will continue and hurdles will be overcome. Currently one of the biggest hurdles is that HDR is limited by methods of displaying images which have a limited dynamic range. Computer screens, LCDs, prints, and other methods cannot accurately display HDR. As a result, methods of converting HDR images into a viewable format have been developed (tone mapping) that allows us to view the images. As technology advances, we will be treated to better methods for viewing this exciting new image format! Of course, if you’re wealthy, you can always go out and purchase an Extreme Dynamic Range LED Display (it claims to provide 10 times the brightness and 100 times the contrast of existing television and computer monitors) now and enjoy it before the rest of us can! Check out their interactive demo which, while it is still limited to your lower resolution computer screen, will give you an idea of what this technology is bringing to us all.
Interested in Learning How to Create HDR Images?
Here are two of the best tutorials I could find:
http://range.wordpress.com/2006/07/15/modern-hdr-photography-a-how-to-or-saturday-morning-relaxation/ **This is an interesting “how to” article based around the use of Photoshop CS2. In the first 12 ½ hours of being posted, this blog article was read 167000 times! This is just another hint to the importance of this awesome technology.
http://hdr101.com/?page_id=4 This one contains a good Photomatix tutorial.
Enjoy!
