Project Index‎ > ‎Course Pages‎ > ‎

HDR Imaging


Author: Brett Castrodale

Introduction

The digital camera and computerized photograph-editing tools have changed photography extensively in the past two decades. These tools themselves are great examples of new media, and deserve attention when discussing new media art. However, digital photography and editing are topics too broad to cover in this presentation. Therefore, I'll focus on a small technique that relies on these tools to produce a photorealistic and artistic effect.

The combination of digital photographs with software that can superimpose images have allowed for a new technique called High Dynamic Range (HDR) imaging. Any camera is only capable of capturing a limited range of colors in detail in a single image. Camera sensors can resolve only a certain amount of detail at each exposure value (i.e. how dark/light an image appears). Details of the darker areas of the picture are best viewed in overexposed pictures (+2EV picture below), and detailed highlights are best viewed at low exposure values (-2EV picture below).
HDR images better represent the accuracy of detail that the human eye sees in a real scene.

HDR imaging eliminates the need to sacrifice detail at the limits of exposure values by digitally enhancing dark areas of photos with information from an overexposed image, by capturing highlight detail from an underexposed image, and then merging this data with the correctly exposed photograph. Programs that can incorporate photographs of various exposures into a single image have existed since 1997. However, these programs have only recently become good enough and inexpensive enough for the amateur photographer to access.

How Does it Work?

Photographs are taken with a digital camera at several different exposure values (EV), which is a measure of how long the light sensor is exposed to light (the shutter speed) and the aperture size (how much light is allowed through the lens). As observed in the pictures below, lower exposure values give darker toned pictures, and high exposure values accent the more brightly lit portions of the scene. In the example below, "Metered EV" is the value at which the camera's computer deems most appropriate for the lighting conditions present. The photographer then adjusted the EV from this baseline. The picture labeled "Metered EV" is responsible for transmitting most of the color detail of the picture because it's the most appropriately exposed photograph.



Then, some savvy use of Photoshop or another image-editing program combines data from input pictures to allow for a larger range of highlights and lowlights. Photoshop allows the photographer the best of all three pictures - stunning highlights, deeply contrasting shadows, and vibrant colors. The final product:

Courtesy Ryan McGinnis, http://backingwinds.blogspot.com/2006/10/how-to-create-professional-hdr-images.html

Uses for HDR

The purposes for incorporating HDR into photographs exist on a spectrum between accuracy and artistry. That is, a photographer may use HDR to overcome a camera's physical limitations and produce a more accurate representation of the object of his or her photograph. The human eye is still much more powerful than any camera lens or sensor. HDR processing looks to close the gap between the images we capture and the real-life objects we see firsthand.


(Courtesy Photomatix, www.hdrsoft.com)
An HDR image of the Eiffel Tower with emphasis on preserving color accuracy and detail.
Note how the detail is extracted from the three photographs on the right, taken at bracketed exposure values.















Alternatively, a photographer may incorporate HDR to make pictures appear artistic. Indeed, many HDR pictures resemble paintings more than photographs.
An HDR image of a Volkswagen Beetle intended to be artistic. (Declan Colohan Photography on Flickr)

Because programs that can process HDR are now more easily and inexpensively obtained by amateur photographers, many people have been able to create beautiful and artistic pictures. In addition, online photo-sharing websites such as Flickr and Picasa have given photographers nearly unlimited space in which to post photographs. But with the good comes the bad....

A not-so-artistic nor accurate HDR self-portrait of a Flickr contributor (Platypus Scooter on Flickr)

Extra detail may not be the most flattering avenue for Platypus Scooter, and the noticeable halo around his head is the sign of shoddy editing work.

Criticisms of HDR

- Overuse - The use of HDR technique is now extremely common on photo-sharing websites. Serious photographers can be critical of HDR's overuse, claiming that it is used unnecessarily when a single well-framed and edited photograph can look more realistic. Often, pictures are taken because they look cool in HDR, not because the topic is actually interesting (for example, our friend Platypus Scooter above). Indeed, after browsing Flickr for HDR images, I grew weary of its use. All the bright colors, contrasts, and overtones got old. HDR often lacks subtlety, which is a very important aspect of photography. Furthermore, poor editing creates noticeable halos around objects in HDR photographs (such as the one around Platypus Scooter's head) which must be painstakingly edited out with Photoshop.

- Fakeness - Many HDR images, especially in the hands of amateur photographers, are obviously "fake." In some situations, such as in the photograph of the Volkswagen above, this is intentional in order to create something that looks artistic. However, many amateur photographers striving for realism often produce an image that appears much different than the source.

- Still shots only - Producing one HDR image requires the camera to take multiple pictures at different exposure values. Therefore, HDR can only be used to shoot relatively motionless scenes. Moving objects in an HDR image can cause blurring and ghosting, which make the final product look odd and sloppy. Consequently, HDR is limited in the types of images it can process. Moving cars or people, sports, action shots - these currently cannot be processed into HDR. Still objects are only so interesting, and with the capability of HDR processing now available to most photographers, there now exist more pictures of sunsets, buildings, flowers, clouds, and lakes than anyone would ever want.



Making your own HDR Photographs

You can make HDR photographs! What you need:
1) Digital Camera. Having an auto-exposure bracketing (AEB) feature is really nice, but at the very least you will need a camera that lets you manually set the exposure value.
2) Tripod. Especially if you're not using AEB, you need a tripod so that each image you take is identical. HDR programs do have a feature that aligns photographs, but it's best not to rely on it. Even professionals who have image-stabilization and AEB features in their camera typically still use a good tripod to get the cleanest shot possible.
3) A program that can merge photos into HDR and then do tone mapping. (Photoshop CS2 and up and Photomatix are the most popular).

The following is a good text tutorial online for making HDR pictures.
http://cajie.blogspot.com/2006/04/hands-on-hdr-high-dynamic-range.html

Two excellent video tutorials, one from the creators of Photomatix HDR software, and then another from photographer Mark Ryan.




My Attempts at HDR
I have an old 4.1 megapixel digital camera without image stabilization, without auto-exposure bracketing, and with a small and only somewhat stable tripod. Consequently, these photographs are not high quality, but you could do MUCH better with a newer camera. You can see the blurring of the tree branches as they/the camera moves during shots. With a camera that has auto-exposure bracketing, each of the three pictures used to generate the HDR image are taken one after another in quick succession, meaning that movement of branches and other objects will be limited.

However, I think these pictures are still pretty cool. (click for high resolution). Shot with a Sony DSC-P73 4.1mp, with manual exposure bracketing. Aligned, generated, and tone-mapped with Photomatix Pro 3.0.



Sunrise from the Old Rag summit


The view from my window

The O'Hill Observatory

O'Hill at Sunset

Alden House

Is HDR New Media?

Photographs using a broad contrast range have existed since the 1850's work by French photographer Gustave Le Gray. Le Gray took photographs of the sea at two different exposure values, one for sky detail and one for sea detail. He then spliced the negatives of the film together along the horizon line to make a very primitive HDR image.

American photographer Charles Wyckoff famously used high dynamic range technology in his 1940's photos of nuclear explosions that appeared on the cover of Time magazine. Wyckoff used a special type of film composed of three layers that responded to different sensitivities of light. This produced pseudo-colored pictures with a large contrast range, but were still inaccurate depictions of the true scene.

Modern HDR processing with computers was researched in the late 1990s by Paul Debevec. Modern HDR programs allow users to easily modify many different parameters of the scene in order to get the colors, shadows, highlights, and contrasts exactly how they want them. This can allow for very fine reproduction of a real life scene.

So is HDR imaging new media? Although the practice of editing photographs existed prior to the digital age, I do believe that digital editing of digital images is new media. Manovich outlines several criteria for new media. (1) Numerical Representation (2) Modularity (3) Automation (4) Variability (5) Transcoding. I believe that HDR processing of digital images meets these criteria for new media. Images exist from their inception as digital data in a computer onboard a camera, and then are modulated by a computer program's algorithm. Digital editing is inherently modular, whereby each image, or even each pixel, can be edited individually. In New Media in Art, author Michael Rush comments
    " Once transferred to digital language in the computer every element of the image can be modified. The image becomes 'information' in the computer, and all information can be manipulated. 'For the first time in history,' says digital media pioneer Peter Weibel, 'the image is a dynamic system. " (Rush 181)

Although the digital image is editable down to the scale of a single pixel (and sometimes down to fractions of a pixel), HDR programs typically automate visual processing so that each pixel does not have to be edited individually - the computer program easily merges photos into an HDR image for the user. Despite the automation, photo-editing programs allow users free reign in the creation of their photographs (variability). Finally, digital images can exist as many different file types and undergo several coding changes throughout processing.

However, is HDR just a digitization of old media? Isn't HDR just pretty photography? Traditional photographers achieved high contrast photographs in pseudo-HDR fashion, so why is this new? I tend to believe HDR is new media because digital tools are used to modify an image which has been for its entire existence just a binary information code. Furthermore, the creation of an HDR image allows the creator a wide range of options in editing the photograph, whereas traditional pseudo-HDR photographers such as Le Gray and Wyckoff edited film and the image they got with that film was what they were stuck with. Now, artists can make several HDR photographs, each with its own focus and appearance, from an identical series of source photographs. The ability to manipulate photographs is made much easier and much more accessible by digital technology, so much so that it deserves to be classified in a different manner than traditional photo-editing.


Thanks!

I encourage you to get out and try making HDR photographs yourself! It's a lot of fun, and you can get some really nice looking pictures.

Some questions for you: Do you think HDR qualifies as new media? What do you think of the HDR technique? Do you like the artistic uses, which emphasize colors at unrealistic levels, or are these images unappealing to you?


Sources:
Rush, Michael. New Media In Art. 2nd Edition, Thames and Hudson, World of Art. Copyright 2005. 29 March 2009.

Comments