Written by Jay Weston on Skilledup.com

HDRI (high-dynamic-range imaging) helps photographers capture more detail and color than is otherwise possible with a single photograph. Using some simple photographic techniques and special purpose software, you can combine multiple exposures of the same scene to create a single HDRI photo that captures the entire range of brightness available. It also allows you to get more creative in how you display the entire range of tonal values and prevents the loss of details and important highlights in both dim and overly bright environments. When color grading or adjusting your image, you can also push things further before you see artifacts like noise or banding.
All this results in a methodology that opens up your creative choices, gives more flexibility in post-processing, and provides a buffer in case of incorrectly exposed photographs. Done incorrectly, HDRI can become much like a generic Photoshop filter effect, but done properly, it can really help you as a photographer to stand out in your own unique way.

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How To Photograph Scenes with Dark and Bright Lighting
One of the goals in professional photography is to capture a specific range of luminosity in a given scene that best matches what we see with our own eyes. If we are taking a photo of a beach at sunset, for example, we might try and capture both the bright sunset and the relatively darker sandy beach. This dynamic range of brightness can go from very high under a bright midday sun (bright highlights and dark shadows, high contrast), to low during twilight or in a dimly lit interior (weaker light sources and lighter shadows, less overall contrast).
What we may often find is that while trying to shoot a high dynamic range scene (one with very bright and very dark areas), the camera doesn’t do as good a job as our eyes in capturing detail in each area. When used in automatic settings, the camera may choose to try and expose the sky correctly, leaving you with an under-exposed, dark beach. It may also try and capture the darker foreground, and the sky becomes overly bright and washed out. Sometimes, either can result to an acceptable artistic effect, but often, you just lose your subject completely.

HDRI in Action!
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A common example of this problem is encountered in architectural or real estate photography wherein you are shooting an interior and also wish to expose a brighter exterior through a window, as in these sample photographs from my own doorway:

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Capturing a Select Range of Luminosity
What cameras typically do is photograph a slice of brightness from a very wide range of brightness values from the real world and store it in a Low Dynamic Range (LDR) format (8 or 16 bit JPGs or RAW files) for an LDR screen. The above images perfectly illustrate two different exposure settings and the range of brightness each can capture.
Your TV or computer monitor can also be described as low dynamic range, as there is a hard upper limit to how much brightness either can display. If there weren’t, those African sunsets on Discovery Channel would blind you.
When you choose your shutter speed, aperture and ISO, this is how you are telling the camera to capture a specific range of brightness. Mess it up and you’ll get either blown out highlights or a dim photograph as the above examples illustrate. This is where HDRI photography methods can really save your work by capturing most, or even the entire range of a scene’s brightness.

How HDRI Used to Be Done
In days of olde when HDRI shooting techniques didn’t exist, you would use a variety of techniques (these are still valid to this day!) to try and reduce the dynamic range as much as possible to display on your LDR medium of choice (whether that was a print or screen).
A common way was to use a flash to light up underexposed areas to reduce the dynamic range or contrast of brightness values — when you’re taking a portrait of someone in front of a bright sunset, for example.
Another traditional technique used to reduce the dynamic range in a photograph is dodging and burning (selectively over- or underdeveloping parts of a photograph in a dark room or Photoshop). You could also get a graduated neutral density filter to darken a bright sky while keeping the ground lighter. The main drawback to these methods is that once you’ve taken that shot, there’s no way to go back and change anything, what you’ve shot is what you’ve got.

Fancy HDRI
So let’s assume you want to use fancy HDRI software and shooting techniques instead. In order to capture a high dynamic range image with a wide range of brightness values from very bright to very dark, we need to actually photograph that range of brightness one shot or bracket at a time. Using the above example, we would shoot at say, 1/1000th, 1/250th and 1/60th of a second, capturing everything from the bright exterior to the darker interior. Later, using special software, we merge these images together to create a single HDR image that contains all of those brightness values.
Where an LDR or 8-bit image might store between 0 and 255 levels of brightness, an HDR image format is 32-bit, and can store from 0 to 20,000 and beyond. That means we can fit a huge range of brightness values into a single image without ever losing highlights or shadow details.

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The above LDR sky contains only pure white in the sun and clouds, or a value of 255. Underexposing this image yields no extra detail. In contrast, the image below it shows rich detail in the sun and clouds because we actually captured those brackets and merged them into an HDR image.

Tone mapping
Once we’ve shot our 3 or more photographs at varying brightness levels, we merge these together to form an HDR image. Strangely enough, while viewing this HDR image, we can still only view one slice of brightness at a time since we are using an LDR display. When viewing an image in its native, 32-bit .hdr format, we have to choose only a slice of that brightness range to display at any one time. If we want to see all the brightness ranges at once, we will need to fuse all of them together into one image. This process is called “tone-mapping”.
The image below, tone-mapped from a 32-bit .HDR image, shows all the details of the doorway shown above. Through the process, both the interior and exterior details are clearly rendered.  The main benefit of doing this using special software is that we’ve quickly shot three brackets at different exposure levels, merged them, and can now move sliders around in order to quickly get both the highlight and shadow details properly exposed.

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HDR lingo
You may find during your research that the term “HDRI” is used interchangeably with “tone-mapping” and “image-based lighting,” which can be somewhat confusing.  This is mostly because “HDRI” is used in two different ways by both photographers and CG (computer graphics) artists. Often, a good rule of thumb is that if you hear a photographer talk about HDRI, then they typically mean the resulting, LDR tone-mapped image. Some people find tone-mapping techniques garish and over the top, others love it, but the results achieved with tone mapping can vary from barely noticeable (above) to incredibly garish and overly done, such as the one below:

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When HDRI is discussed by CG artists, it often refers to using 32bit .hdr images for image-based lighting, in order to light a three-dimensional computer generated scene:

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Difficulties with HDRI Photography
This all sounds great, but what are the downsides?
1. Moving objects like people, clouds and trees create unwanted ghosting effects, as they move between each bracket.
2. Requires a tripod (most of the time) to align each bracket.
3.Data and file management translate to at least 3x the number of files compared with “normal” photography.
To mitigate these drawbacks, always use a tripod, try not to shoot scenes with a lot of moving objects (or look out for “deghosting” options in your software of choice), and try using a camera with a high FPS (frames per second) shooting speed. This will significantly reduce ghosting. However, ghosting is simply impossible to remove in some cases such as a moving car, cyclist or person.

Where to start?
HDRI Photography is a fun hobby and can be a lucrative profession, so here are some resources to help you get started.
1. The best book ever written on the subject is possibly The HDRI Handbook 2.0 by Christian Bloch. An associated website, HDR Labs, offers an amazing range of resources.
2. To capture your HDR image, you’ll want to look into how to use bracketing with your camera and become proficient in using M (manual) mode.
3. To assemble the image, Photomatix is a very popular and easy-to-use program. Adobe Photoshop also does a great job, and there are scores of other options out there. Again, Christian’s site and book will help you in this area.
4. To process and organize your photos, we recommend that you use Adobe Lightroom.  However, Adobe Bridge or any other RAW converter software will do just fine.
5. You can download and play around with a large number of free HDR images in the HDR Labs archives. These are meant for image-based lighting, but you can load them up and play around with them in Photoshop/Photomatix and see what a well- captured HDR image looks like. You can even tone-map these images yourself without having to shoot the images.
6. If you’d like to see one of the best HDRI photographers around, Trey Ratcliff is very popular and is a great resource for HDRI photographers. In addition to giving advice on HDRI, Trey also reviews camera gear and more.
7. If technical stuff excites you, check out HDRI: Acquisition, Display, and Image-Based Lighting, one of the best books on the subject.
8. If the image based lighting or research sides interests you, Paul Debevec has some very interesting projects worth checking out.
There’s quite a bit of technical detail to be learned, and you might want to check out an online course in HDRI. Regardless, I hope you grow to enjoy HDRI as much as I do. If you have any questions or ideas about HDRI, please post them in the comments below!